Potentiometric Titrations E. C l i f f o r d Toren,
Jr., Departmenf o f Chemistry, D u k e University, Durham, N. C.
T
LITERATURE covered in this review includes recent developments which became available since the review by Roe (221) and continues through the literature reported in Chemical Abstracts through November 20, 1967. Potentiometric titrations and potentiometry were reviewed by Banick (15), Gross and Murray (88), and Hilton (105). Acid-base titrations and p H measurements were reviewed by Bates (16), Hahn (91), and Wimer (281). Redox titrations were reviewed by Strickman (256) and Headridge, Pierce, and Anderson (96). Electrode sign conventions were briefly treated by Van Rysselberghe et al. (269).
HE
TITRATION CURVES AND EQUILIBRIUM CALCULATIONS
With the increasing availability of computers and computer programs, equilibrium calculations and titration curve interpretations have become less tedious. Romary, Xndrews and Donnelly ($63) have developed programs for use on the IBM 1620 computer using potentiometric data t o calculate the following: Bjerrum and theoretical complex formation curves, complex formation constants from simultaneous equations and successive approximations, theoretical and formation curves for acid dissociation constants, and acid dissociation constants from simultaneous equations. Bishop (22) has programmed the parameter Q, the quality of a titration, for symmetrical ion-combination reactions. The Q function is useful for determining the feasibility of titrations and for adjusting conditions to meet a given feasibility (precision). Bishop concludes that it is particularly advantageous t o work on the microscale and t o use a large titrant/titrand concentration ratio. Acid-Base Titrations. Butcher and Fernando (32) developed FORTRAN I1 programs for precise calculations of the effects of dilution and ionic strength in the titration of monoprotic acids. The authors conclude that the maximum buffer index, Pmax, does not occur at half-neutralization, nor when pK, = pH, if dilution by the titrant is considered. Ionic strength effects cause omaxt o be significantly larger and to come somewhat earlier than if activity effects were not considered. The sharpness index, 7, is not appreciably 402 R
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affected by ionic strength; however, the pH a t which qmax occurs is significantly affected by ionic strength. Dilution significantly affects as would be expected. A simplified treatment of acidbase titrations is also given by Butcher and Fernando (33). Theoretical end point errors are calculated for monobasic and dibasic acids and for monoand diacidic bases without including activity considerations. A somewhat novel approach t o acidbase calculations is described by Waser (275). The volume of acid or base is calculated t o reach a given p H to avoid the problem of solving equations in high orders of H+ concentration. By addition of two distribution curves, one for the solvent and one for the acidbase pair, the titration curve is readily obtained. The chief advantages of this method are that points near the origin are readily examined and that relatively simple mathematics are required. This analysis presents the possibility of esperimental verification by using a p H stat for the preparation of the distribution curve. One must also tend to agree with Waser, “...it would appear that everything of interest about the computation of acidbase titration curves has already been said...”. Jenkins and Latham (f20) interpreted potentiometric data near the equivalence point by a relatively simple procedure to obtain K , and various K,’s and KaP’s. The derivations assume media of relatively constant ionic strength-Le., that the ionic strength is constant from 90 to I I O ~ o titrated. This rapid procedure yields results within 0.1 pK unit as compared t o accepted values. Cohen (40) presents a simple graphical method to locate the end point in potentiometric titrations by averaging points of a conventional AE/AV us. V curve on both sides of the equivalence point. The method is applicable to both symmetrical and unsymmetrical curves. In a recent communication, Ojeda, Perez, and Wyatt (188) point out that the sharpness of end points can be enhanced by using large salt concentrations in titration of neutral bases. Similar enhancement can be achieved by addition of sugars. The results are interpreted on the basis of the reduction of the hydration of the proton. Schwabe (237) discusses acidity in concentrated salt solutions. Potentiometric data show that the p H can be considered as -log a=+ in these media. I n
this instance the effects are interpreted as primarily electrostatic. Tanaka and Yakagawa (261) derived equations for the potentiometric titration curve of bases in acetic acid solvents using perchloric acid titrants in the presence and absence of water. The potentiometric sharpness index and titration errors are also predicted. For solutions containing an exes3 of water, the “ligand buffer” concept can be used in calculations after the equivalence point. The net effect is t o reduce the sharpness index and t o cause negative errors. Polyelectrolytes. Shatkay and Michaeli (241) have derived a general equation t o describe the potentiometric titration of polyelectrolytes undergoing precipitation in terms of the average degree of polymerization, pH, the degree of deprotonation of polymer in solution, and the chemical potentials of the polymer and the proton. The titration curve of poly(diethylaminoethy1methacrylate hydrochloride), poly(DEAEM-HCl), agreed with the theory. A significant analytical development is preqeiited in a following paper (240) in which poly(DEAE1I-HCI) serves to enhance the end point in the titration of dilute weak acids. Equations were derived t o describe these curves. The effect of the polyelectrolyte wa5 to cause the portion of the titration curve immediately preceding the equivalence point to be horizontal followed by a steep vertical break a t equivalence. The similar application of poly(2-vinyl-pyridine) was also suggested. Kono and Ikegami (134) interpreted the potentiometric titration curves of poly(L-glutamic acid) in the presence of divalent cations. The amount of cation bound to the polymer was determined. KO specific interactions between the cation and the polymer in either random coil or helical conformation was observed; however, the fraction in the random coil form a t a given pH was especially changed by the addition of Mg(I1). Tokiwa and Ohki (264) used a modified foim of the potentiometric equation for polyelectrolytes to account for the formation of micelles in the titration of dimethyldodecylamine oxide. From the degree of protonation of the monomeric and polymeric fractions, it was possible to obtain a;] individual titration curve for the micelles from which reasonable values for the surface potential of the micelle could be obtained. Redox resins prepared by
the condeii~ationof hydroquinone and forinaldehyde were studied by Maiieckc, Focrstei, and Panoch (157) by potetitiomctric titrations with Cr(V1) and Ti(II1) in acetic acid-water. The titration curves agreed with appropriately modified forins of the h'ernst equatioii. Compleximetric Titrations. Hannema and den 13oef (93) derived equations for the potentiometric titration of mixtures of metal ions with disodium [ (carbosymethyl)imino] bis(ethylen e n itrilo) tetraacetate using the mercury indicator electrode. Espei imental verification of the theoretical curves was given for mixtures of 8 X l O - ' X Pb(11) and Hg(I1). The results for a Cu(I1) titration with EDTA ivere predicted by the derived equations. Potentiometric titrations of metal perchlorate - tetrabutylammoniurn EDT.4 mixtures in t-butyl alcohol using a glass electrode wiih tetrabutylammonium hydroxide as titrant were reported by Marple aiid Scheppers (160). The Mg(II), Cu(II), Ca(II), and Cd(I1) perchlorates in excess over the (Bu4N)2H2Y cause a large initial increase in acidity, which results in the first break of the titration curve corresponding t o the titration of the perchloric acid thus formed. Subsequent breaks correspond t o JIH?Y 213~4NOH= (Bu&)JIY 2H20. This method seems t o offer great promise for metal ion titrations in nonaqueous media. Redox Titrations. A general equation t o formalize the potentiometric titrations of homogeneous, symmetrical couples is given by Goldman (81) in terms of potential us. the fraction titrated. The fraction titrated is expressed in terms of either the potential of the indicated couple or the equivalence point potential. I n a later paper (82),the effect of concentration on the equivalence point potential and equilibrium constant is derived; no concentration effect is observed for symmetrical, homogeneous couples. The conditions for sharp end point breaks are discusqed. Geyer and Peker (76) discussed the dependence of redox equilibria on the activity of the couples. Straight-line graphs of potential changes due to activity us. the logarithm of the activity quotient are obtained. .4 similar treatment for the linear titration curve of the Mn(I1)-Mn(II1) couple is presented.
+
+
ELECTRODES
The major development in potentiometric titrations is undoubtedly in the field of ion-selective electrodes. In a recent survey (37),it is reported t h a t the total of these electrodes is expected to double ill the near future. The present status is reviewed, and is probably out of date at this time. Ion-selec-
tive electrodes are also reviewed by Oehme (185). An excellent, well illustrated feature article by Rechnitz (212) serves as a guide t o the theory, preparation, and application of all types of ionselective electrodes. The classification of these electrodes is used in the present review,-Le., glass, liquid-liquid, and solid-state or precipitate membrane electrodes, Additional information about ion-selective electrodes is available from the major manufacturers. Glass Electrodes. Several excellent books have recently appeared on the subject (62, 63). Mattock (166) has reviewed the applications of glasq electrodes with primary emphasis on electrodes not responsive to H+. Camman (34, 35) reviews the theory and application of glass electrodes. A discussion of the alkali and acid errors of pH electrodes is given. A short but salient discussion of the mechanism of glass electrode response is given by Durst (59). Most of the work in fundamental studies of p H glass electrodes continues in the interpretation of the acid aiid alkali errors. Lengyel, Csakvari, and Toperczer (145) employed radiochemical measurements with **11'a+on MacInnes-Dole glass t o obtain good agreement with results from potentiometric measurements. The mole fraction of N a + on the surface layer approaches unity with increaqing pH. In further studies (144) the acid as well as alkali error was esamined with tritium and K a + tracers. They observed that the activities of alkali metal ions were strongly dependent on the amount of the ions in the surface layer, but that the H + activity remained constant. At low p H values, the acid error mas observed af the tritium concentration passed through a minimum, a tritium minimum was also observed a t high p H values to correspond to the alkali error. Divalent ions in the glass were found t o modify the equilibrium constants of the ion exchange process and the activation energy of the glass. I n similar studies of the alkali error, Csakvari, Dobos, and Pekari-Kerepesi (44) determined that the activity coefficient of Li+ in the surface layer depends on the mole fraction of Li+ in the layer. Agreement mas obtained between surface concentrations and poteiitiometric data. Boksay, Bouquet, and Csakvari (26) related thermodynamic measurements of the activity coefficient of alkaline solutions to Jordan's empirical equation of the alkaline error. Light and Fletcher (147) determined the pH response and alkaline error for commercially available electrodes in high ionic strength media for cells without liquid junctions. Hydrogen electrodes were not required in this method and accuracies were of the order of 0.001 pH. One electrode examined
showed an efficiency greater than unity. The tip potential for glass microelectrodes is found by Agin and Holtzman ( 2 ) t o arise from an interfacial potential between the glass and the electrolyte. The potential can be eliminated by small concentrations of ThC14 or CaC12. More precise values of p H as well as faster responses were claimed by Douheret (52) if the glass electrode was filled with methanol rather than water for measurements in very acid, alkaline, or anhydrous media. An empirical equation was developed by Xoore and Ross (177) to relate solution composition of NaCl and KCl mixtures to the observed potential of a potassium electrode. The selectivity coefficient was found to vary with composition and the age of the electrode. Rechnitz and Kugler (216) reported selectivity ratios for cation-sensitive glass electrodes in ethanol-water media. The response to Li+, Na+, K+, Rbj-, Cs+, and S H 4 + increased with ethanol concentration because of the increased liquid junction potential. I t is suggested that F a + as opposed to H + be used as the reference ion in mixed solvents. Rechnitz (213) summarized much of the theory aiid application of cationsensitive glass electrodes with emphasis on the analysis of alkali metal cations. The effects of mixed solvents and application to ionic equilibria are discussed. The theory of the response time is elucidated as well as the application to kinetic experiments involving large rate constants. The kinetics of the reaction of alkali metal ions with tctraphenylborate were examined. JIore detail on the kinetics of tetraphenylborate \vas given in a later paper (154). With the flow system described, secoiidorder rate constants approachiiig 106M-lsec-l could be obtained. Rate measurements were not limited by the response characteristics of the glass electrodes with this technique. Gcrchman and Rechnitz (75) employed a cation-sensitive glass electrode to indicate the argcntometric titration of cyanide. The electrode indicated both end points with equal precision as compared to the silver electrode and is not subject to redox interferences. Townsing, Posner, and Quirk (265) made detailed observations on the calibration of the sodium glass electrode in simple solutions and in mixtures conK+, Mg?+, Ca2+, I3a2+, taining "+, C1-, and S042-. With proper calibration or adjustment of ionic strength it was possible, e.g., to determine K+ concentrations with relative errors of =t1%. Johannesen, Aslakscn, and Thom (122) used direct potciitiometric measurements with a sodium glass electrode to determine N a + in four concentration decades in chloride, lactate, and bicarbonate infusion solutions. Fused VOL. 40, NO. 5, APRIL 1968
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mixtures of sodium and potassium chlorides at high temperatures were investigated by Foerland and coworkers (68, 69) using an alkali-glass membrane sensitive to sodium. The electrode exhibited large positive deviations from the Nernst slope which were attributed to liquid junction potentials. Hladik, Saunier, and Morand (107) found that membranes of quartz, borosilicate, and Vycor glasses responded to changes in silver ion concentration in fused sodiumpotassium chloride melts. Only the quartz membrane followed the Nernst slope at temperatures near 900' C. The preparation of a sodium electrode is described by Dutz (60). Combined measurements of N a + and H + response were used to interpret the mechanism of the electrode response. A combination sodium microelectrode is described by Henderson (99). Both papers discuss the applications of these electrodes. Nakamura (180) described glass electrodes with good sensitivity and accuracy for the measurement of N a + and K+ in biological fluids. It was found that the selectivity is a simple function of the univalent cation to Al(II1) ratio in the Si02matrix. The preparation of glass electrodes for the detection of the divalent cations of calcium, magnesium, barium, strontium, manganese, and zinc was described. The ratio of uni-, bi- and trivalent cations introduced into the alkali aluminosilicate glass determined the selectivity of these glass electrodes. Liquid-Liquid Ion-Exchange Electrodes. Although other ion-selective electrodes are available, most of the liquid-liquid types described were calcium ion electrodes. Ross (225) discusses the application and preparation of calcium electrodes using liquid, substituted phosphoric acid ion exchangers. In a patent (ZSg), the fabrication and application of liquidliquid electrodes selective to alkaline earth ions is described. Liquid-liquid interfaces were obtained by direct contact or through cellophane membranes. Selectivity coefficients of several cations were reported. Glauser et al. (80) used calcium electrodes to study compleximetric titrations. The electrode was found useful for the evaluation of stoichiometry and stability of calcium complexes of various ligands. The usable conditions were reported to be between p H 5 and 7 for calcium ion concentrations in the range of 10-l to 10-5M. King and Mukherji (130) described the compleximetric titration of calcium with EDTA at p H 10. Results were improved by the presence of alkali metal ions. Ba2+ Mg2+, and Zn2+ were titrated to a single equivalence point as indicated by the Ca2+response. Precipitate and Solid-state Electrodes. Shatkay (239) compared 404 R
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commercial liquid-liquid type calcium electrodes with electrodes fabricated from paraffin and solid polymeric membranes. The paraffin membrane was not useful below 2 x 10-3.1f CaZ+; however, reproducible performance for the commercial and polymeric membranes was observed down to 5 X 10-5M. The paraffin electrode was completely nonspecific even in the presence of 10-3J4 foreign salts. The other electrodes were selective with foreign salt concentrations less than 10-1M. Pungor and Havas (203) reviewed the literature of ion-selective membrane electrodes and discussed the preparation and characterization of the membranes. The response time, memory effects, and detection limits were discussed. They propose a model in which potentials on either solution-membrane boundary are independent of each other. Several experiments are presented to confirm the model. Theoretical equations are derived from thermodynamic considerations to predict electrode response, as reported in earlier work (205). Electrodes selective to C1-, Sod2-,OH-, H+, K+, Na+, ZnZ+,Niz+,and id3+,are prepared (20.4)by impregnating silicone gum rubber membranes with the corresponding salts. Concentration u t . potential plots agreed with Xernst equation down to lO-4M. The ion transport phenomena were discussed. Rechnitz et al. describe the selectivity, sensitivity, and response characteristics of electrodes selective to iodide (215) and to bromide and chloride (214). The electrodes are prepared by incorporating AgI, AgBr, and AgCl, respectively, into the silicone rubber matrix. Selectivity ratios for the various electrodes were reported with response times, t112, of 8,14,and 20 seconds, respectively. The lower limits of Nernstian response were lO+M I-, 5 X lO-4-V C1-, and 7 X 10-5JI Br-. Geyer and Syring (77) have reviewed the literature and discussed various means of preparing membrane electrodes. Membranes with metal oxides and hydroxides are incorporated into matrices of polyethylene, paraffin, and agar. The electrodes showed reversible behavior and were employed in many acid-base and precipitation titrations. Rlaterova and coworkers have studied membrane electrodes prepared from ion exchange resins incorporated in a polystyrene matrix. Beryllium electrodes (ZO), chloride electrodes (163) prepared from several anion exchange resins, and nitrate, nitrite, perchlorate, and iodide electrodes (162) were described. The electrodes described above were in general not sensitive below ca. 10-3M. These and similar electrodes (161) were used in the precipitation titrations of CaZ+, Zn2+, F-, C1-, Br-, I-, and
NO,-. Resin type, cation exchange electrodes were evaluated in acetone and methanol solvents (84) and in acetic acid solvent (83), and a t high temperatures (85) by Gordievskii, Filippov, and Shterman. The theory of uniunivalent precipitation and potentiometric indication by ion exchange membrane electrodes was elucidated by Ijsseling and van Dalen (110). The influence of diffusion coefficients and concentrations of the ions, and of the capacity of the resin on the shapes of many theoretical titration curves was examined. Several novel membrane electrodes have also been recently described. In a patent, Gregor and Schonhorn (86) describe electrodes prepared from membranes of barium stearate, calcium or iron(II1) palmitates. Liteanu and Mioscu (151) described parchment membranes impregnated with barium sulfate, which were useful for strong acid or base titrations. Bases were titrated with sulfuric acid and acids were titrated with barium hydroxide since the membrane mas impermeable to barium and sulfate ions. Nukherjee (179) employed clay and ion exchange membranes for the determination of the ionic activity of clays and other colloidal suspensions and for the potentiometric indication of precipitation and acid-base reactions. A colloid film electrode for the titration of organic bases in benzene, chloroform, and acetone solvents was described by JValigora and Paluch (274). Buchanari and Seago (SO) described electrodes with metal membranes reversible to the ion of interest. Copper, cadmium, silver, and thallium couples were investigated. This type of electrode must be completely reversible to the metal ion, and air must be rigorously excluded. Xost of the literature coiicerning solid-state, ion-selective electrodes has been concerned with fluoride measurements. Single crystals of LaF3, SdF3, and PrF3 were found by Frant and Ross (71) to be highly selective to F- in concentrations down to 10-5Jf. The response of the electrode was improved by doping with Eu(I1). Lingane (148) used a commercially available fluoride electrode for potentiometric titrations with Th4+, La3+, and CaZ+. The best results were obtained with La(S03)3. The equivalence point potential was determined within =t2 mV and an accuracy of better than 0.1% was noted in neutral unbuffered solutions. Trace quantities of fluoride in tungsten were determined by direct potentiometry (206). Other Hydrogen Ion Electrodes. Villarreal (270) proposed the use of the Cu/Cu stearate couple for the potentiometric measurement of pH. The emf of the Cu/Cu stearate/?;a stearate ( 10-3-lf) reference electrode was re-
poitcd to bc -0.1546 T' 2's. S H E . The s j stmi is mcc'hanic~allystable a i d can be
u 4 111) to '70" C. A coi)pcr-SCE sy>tcni w a h L I in ~ the potentiometric determination of pota.siuni carbonate (271). The electrode !$as reported to be ca. thice times more sensitive than the glass-SCE pair. Podbornov and Titov (197) report that a tungsten electrode with a nickel, graphite, stainless steel, or silite reference electrode exhibited nearly linear response with p H in the range of 3 to 9. -4bismuth electrode is reported to be superior to a glass electrode in that faster response is obtained in alcoholic-benzene solutions (153). An oxidized platinum electrode was reported (194) to exhibit higher sensitivities than glass electrodes in many nonaqueous solvents. Surface active anions interfered whereas cations did not. Platinum electrodes were used in strong acid-strong base titrations with coniparable accuracy to glass indicator electrodes (11). A platinum electrode was reported (67) to yield linear p H response in acid-base titrations with hydrogen peroxide present. Oehme and Hegner (186) described a hydrogen electrode for precise measurements. The system is designed for the rigorous exclusion of oxygen. Von Sturm and Weidlich (258) described a hydrogen electrode in which activated nickel was used instead of platinum-black. Herlem (100) described a hydrogen electrode suitable for use in liquid ammonia or liquid sodium iodide ammoniate. Metal Indicator Electrodes. T h e electrodes discussed in this section are classified alphabetically according t o the elemental electrode material. Hakoila (92) described the application of a barium amalgam electrode t o indicate equivalence in a barium sulfate titration. The magnitude of the potential break \vas found to vary with temperature, pH, and the surface area of the barium amalgam. Hagyard and Chapman (90) found that when a passivated cadmium electrode was sliced in a CdClZsolution by a ruby, the reversible potential was attained within 10-30 psec. Takeuehi and JXiwa (260) used a glassy carbon electrode us. a platinum reference electrode for the potentiometric titration of aromatic amines by diazotization with sodium nitrite in acid media. The theory and application of mercury electrodes for compleximetric titrations is reviewed by Vandenbalck (268). Mercury(1) and gold(1) acetate electrodes were found reversible to acetate ion in anhydrous acetic acid (112). Nercury(1) formate, acetate, and propionate (36) were found reversible t o the corresponding anion in aqueous media. Both papers report standard potentials for the couples.
Schmeckenbecher and Liiidholm (2%) employed a palladium electrode in the potentiometric titration of dimethylamine borane and hypophosphite. A PdC12 and FeC12 mixture was titrated with dimethylamine borane and hypophosphite solutions. The potential break is believed to occur by the interaction of Hz generated on the palladium surface when excess dimethylamine borane is present in the solution. Hoare (109) attributes the enhanced reversibility of the pre-anodized platinum electrode to O2 dissolved in the platinum metal as opposed to 0 2 adsorbed on the surface. Bontron (27) found that a platinum electrode immersed in an Fez+-Be3+solution reached 30y0 of its equilibrium potential within 20 psec., but did not attain equilibrium until 20 msee. The response of the electrode varied with pretreatment. Strafelda and Matousek (255) titrated Pbzf, Zn2+,Cd2+,Hg2+,and Sc3+ with EDTA using a platinum electrode in the presence of copper(I1) or iron(I I I) complexonate. Olsen and Adamo (190) employed a silver electrode in the presence of a trace of Ag+ for the automatic potentiometric titration of h4g2+, Ca2+, and Ba2+ with (diethylenetrinitri1o)pentaacetic acid. Symmetrical titrations curves were obtained and the electrode is reported to have the advantage over a mercury electrode in that the solutions need not be deaerated. For metal ions with large formation constants, a back titration procedure was required. Luca, Magearu, and Popa (152) determined the successive formation constants of Zn(II), Co(II), and Ni(I1) ammines with the Ag/=lg(SH3)2+/NH3 electrode. Thiosulfates were determined by direct potentiometry (155) with the Ag/Ag (S2 0 3 ) z 3 -/S2032 - electrode. Only anions that react with Ag+ interfere. Marple (159) examined the chloride response to the -4g-AgCl electrode in water-ethanol mixtures. Negative deviations from the Nernst slope were observed until the ethanol content approached SOYo. A thallium electrode was used by Konrad (135) for the continuous determination of Oz dissolved in water. The thallium metal is oxidized by Oz to produce thallium(1). Only sulfides and mercaptans interfered. Kolodney, Minushkin, and Steinmetz (132) described a thorium oxide indicator electrode that responds to O2 in liquid sodium. The emf is a linear function of the logarithm of the O2concentration. Copper/copper(I) oxide was used as the reference electrode. Rusina, Ivanova, and Kovalenko (226) examined bimetallic electrodes for the potentiometric titration of the iodine produced from the Zn2+-K3Fe(CN)6-KI reaction by titration with thiosulfate. Satisfactory combinations were Pt-Zn,
Pt-Pb, Pt-Cu, W-Ni, and W-AI. These authors (267) also applied an aluminumcalomel electrode combination in the determination of copper, zinc, and lead with anthranilic acid. Reference Electrodes. Very few new developments have been noted in this area. T h e most popular electrodes continue to be the calomel and silver-silver chloride electrodes or variations thereof properly modified for use in a given medium. Durst (58) discussed the advantages of porous ("thirsty") glass salt bridges over the conventional agar bridge. The chief advantages are that the bridge is more inert, can be used with nonaqueous solvents, can be used a t elevated temperatures, and can be stored with little or no change in its characteristics. The construction of several bridges is illustrated. Another salt bridge is described in a patent by Leonard and lT7atanabe (146). -4ceramic barrier is fused t o the glass portion of the halfcell structure so that the barrier leaks at the desired flow rate. The flow rate of saturated KCl is reported t o vary from 0.01 t o 0.1 ml in 24 hours, and the resistance approaches 1500 ohms. The junction is easily cleaned and resists clogging in slurries. Shams-El-Din, Kamel, and Abd-ElWahab (262) report that metal impurities in the mercury phase of saturated calomel, Hg/Hg2S04and Hg/HgO electrodes alter the initial potentials of these reference electrodes, but that the electrode slowly approaches its normal potential. The time required depends on the metallic impurity and the amount present. Initial potentials are very close to the expected reversible impurity potential. These authors caution that ample time should be allowed for the amalgamated impurities to be discharged, if impure mercury is employed. The standard potential of the calomel electrode was carefully investigated by Covington, Dobson, and Rynne-Jones (42, 43). It was observed that the electrode develops a small mercuric ion concentration ca. lO-*Jf from the disproportionation of calomel. These authors suggest that fresh electrodes be prepared for use a t a given temperature because excess mercuric ion results at higher temperatures and remains if the temperature i3 lowered. Copello and Dorfman (41) used a glass reference electrode for the potentiometric titration of cyanide and chloride with silver. -4 review of these titrations was also given. Smyrl and Tobias (248) report that thallium amalgam/thallium(I) chloride or iodide electrodes are suitable references for use in dimethylsulfoxide, if the amalgam is protected from oxidation. hlarple (158) concludes that cadmium amalgam/cadmium chloride electrodes VOL. 40, NO. 5, APRIL 1968
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are suitable for use in anhydrous dimethylformamide; however, Breant and Nguyen-Van-Kiet (29) caution that mercury(I1) oxidizes the formic acid produced in the D h l F decomposition with water present. The mercury/mercury(I1) reference cell is useful if prepared fresh daily. DeRossi, Pecci, and Scrosati (49) report that the silver/ silver chloride electrode is suitable for use in formamide and that it equilibrates more rapidly than either the calomel or cadmium/cadmium chloride electrode. Every and Banks (66) investigated the mercury/mercury(I) sulfate and the noble metal oxide electrodes of gold, platinum, and rhodium as references in sulfuric acid media. These electrodes are convenient because they are solid, insoluble in sulfuric acid, require no salt bridge, and are relatively unaffected by the sulfuric acid content (96-100%). The mercury/mercury(I) sulfate electrode reproduces t o within i10 mV and is insensitive t o temperature; whereas the metal-metal oxide electrodes vary 1 2 0 mV and are linearly dependent on temperature. SOLVENTS A N D REAGENTS
Since the topics in this section are discussed elsewhere in this issue, only pertinent references with especially novel approaches, reagents, or solvents will be discussed. Nonaqueous Solvents. Most of the work in this area continues to be primarily concerned with acid-base titrations. Pietrzyk and Belisle (196) investigated aromatic sulfonic acids as titrants for organic bases in acetic acid, acetonitrile, chloroform, and methylisobutyl ketone. -4s a titrant, 2,4dinitrobenzenesulfonic acid was found t o be nearly as strong as perchloric acid. Tetraethoxy- and tetramethoxysilanes were employed as solvents for the titration of weak bases with a perchloric acid-dioxane titrant (219, 220). Methyl thiocyanate was used as asolvent for very weak bases (pKb < 13) by Jasinski, Smagowski, and Korewa (118).
Metal ions have been determined (117) in nonaqueous solvents as acids by potentiometric titration with bases. Many metal halides were titrated in pyridine, butylamine, morpholine, and dimet hylformamide with potassium methoxide or tetrabutylammonium hydroxide using glass or antimony electrodes. Metal halides and nitrates were similarly titrated in dimethylsulfoxide (119). Rare earth nitrates were determined by Kreshkov, et al. (141) in methanol-acetone solutions by titration with tetraalkylammonium hydroxides. Schlegel (231) discussed the titration of the dichromate ion as a Lewis acid with carbonate ion in fused sodiumpotassium nitrate melts.
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ANALYTICAL CHEMISTRY
Several applications of redox titrations in nonaqueous solvents have recently appeared. Kratochvil, Zatko, and Markuszewski (137) used copper(11) perchlorate as an oxidant t o determine hydroquinone, thiourea, and tetrabutylammonium iodide in acetonitrile. Iron(I1) chloride was used (210) to titrate cerium(1V) in an acetonitrile medium. Cobalt(I1) and manganese(11) were determined by oxidation with K3Fe(CS)G in various amino-alcohol solvents by Herman, Sulcek, and Zyka (101). The best solvent was found t o be tris (hydroxyethyl) amine. Hladky (108) investigated the application of Cu(II), Fe(III), Br2. and I2as oxidants in dimethylformamide for the determination of organic reducing agents. Sn(II), V(III), and hydroquinone were used as reducing agents and Cu(II), Fe(III), and quinone were used as oxidizing agents in a pyridine solvent. Reagents. Sodium diethyldithiocarbamate was employed b y Staroscik and Siaglo (252) for the potentiometric determination of trace quantities of indium, and by Trivedi, Soni and Bhatt (266) for the determination of mixtures of silver, copper, zinc, and lead. Kalbus and Kalbus (124) used dithiooxamide to determine silver in the presence of many other cations. Thiourea was used by Shul’man, Savel’eva, and Igrunova (244) for the determination of low concentrations of silver, mercury(II), and copper(I1). Silver was selectively determined with 1,2,3benzotriazole by Havir (95). Wilson and Fennel1 (280) studied the acid properties of the interaction products of 1,2,3-benzotriazole hydrochlorides and cyano metal complexes by titration of the products with sodium hydroxide. Hexamminecobalt(III)tricarbonatocobaltate(II1) is described by Baur and Bricker (19) as a weak oxidizing agent in neutral solution, and as a strong oxidant in acid solution for titrations of Fe(II), V(IV), and Ce(II1). Zatko and Kratochvil (287) used V(II1) for the reduction of perchlorate in the presence of osmium tetroxide for the subsequent potentiometric titration of the chloride produced. Sodium peroxomolybdate was used to titrate arsenite directly with iodide catalyst (136). Rao (208) has critically reviewed potassium dichromate as an oxidant. Rao and Rao (209) used potassium dichromate in 8-12M phosphoric acid t o oxidize V(II1) t o V(V) with two potential breaks. Mixtures of V(II1) and V(1V) were thus determined. Sodium nitroferricyanide was used (228) in the titration of copper and zinc at micromolar concentrations. Iodine monochloride was used (238) for the titration of W(II1). Under appropriate conditions, potential inflections were observed corresponding t o W(1V) , W (V), and W (VI).
Ottaway and Bishop (191) critically examined the titration of Fe(I1) with potassium bromate. Phosphoric acid catalyzed the reaction which was fomd to be first-order in Fe(II), Br2, and phosphoric acid. Cu(I1) caused negative errors in the determination. Rao and Sarma (211) observed that CuS04 catalyzes the reduction of V(V) by thiosulfate t o permit potentiometric titration. Sorkus and Stulgiene (183) catalyzed the reduction of chloramine T and sodium hypochlorite by arsenite with osmium tetroxide t o permit successive determinations. Standard Buffers. K i t h the increasing application of partially aqueous and nonaqueous solvents, the establishment of standards and acidity scales are becoming increasingly important. A summary of the work in this area a t the Sational Bureau of Standards (17, 18) has been reported. Woodhead et ul. (284) reported on buffer solutions of tris (hydrouyniet hyl) amino methane for pH measurements in 50% methanol. NcIlvaine buffer values were adjusted from the S$rensen pH scale t o the British Standard scale by Whiting (279). Popa, Luca, and Enea (198, 199) examined potassium acid phthalate buffers in 43.370 methanol solutions and borax buffera in 10, 20, 409;b methanol solutions. pH values of buffers were standardized by Kryukov, et al. (142) for temperatures t o 150’ C. TECHNIQUES
The references cited in this section deal with the theory and applications for methods other than classical potentiometric titrations. The confusion in terminology for the technique involving the measurement of the potential difference between two polarized electrodes still persists. This technique has been called “differential electrolytic potentionietry,” “polarovoltry,” “biopotentiometry,” and “constant current potentiometry.” The reviewer pleads, as did his predecessor (221),for one term t o prevail. The first or last terms are both well suited for keyword indexing, the third term is quite analogous t o the amperometric situation and the second, though apt, does not settle pleasantly in one’s ear. Constant Current Potentiometry. Bishop (23) examined the technique as a linear diffusion process based on the Kernst diffusion model. Calculated and experimental results were in good agreement. Optimum experimental conditions were also discussed. Ariel and Kirowa-Eisner (12, 13) applied the technique with several types of mercury electrodes for acid-base titrations with coulometric generation of titrant. The preparation and placement of the electrodes were discussed. In a later paper,
these authors (131) employed twin mercury electrodes a t zero applied current to obtain sharp peaks a t the end point. The peak arises from the small difference in the rates of the two electrodes both of which give sigmoidal titration curves. Dubois and Lacaze (54-56) discussed the general principles of the method and several applications including redox and acid-base examples. Rlonien and Specker (176) employed the technique for the trace determination of chloride with coulometric generation of silver. Selenium(1V) was determined by titration with potassium iodide using both amperometry and potentiometry a t two polarized electrodes (1). These combined techniques were also compared for the titration of mercury (I),thiocyanate, antimony(III), and thallium(1) with iodate (72). Songina and Khalitova (249)determined thallium(1) with polarized platinum electrodes by titration with potassium permanganate or bromate; and thallium(II1) by titration with Complexon I11 (250). Whiteker and Murphy (278) determined uranium(II1) and (IV) mixtures using constant current potentiometry with iron(II1). I t seems to this reviewer t h a t the principal advantages to be gained by this technique are realized in the application to irreversible couples and to coulometric generation of titrant. I n the latter case, the noise produced by the generator electrodes would tend to be minimized. Micro-Methods. Helbig (97) reviewed the application of electrochemical techniques to ultramicroanalyses. He observed t h a t in titrimetric methods, owing to the small quantities involved, visual indicators are difficult to use with the result t h a t electrometric methods are preferred. A procedure for the titration of nanogram amounts of copper is described
(98). A procedure for the determination of microamounts of iron(I1) using dilute dichromate titrants is described by Close et al. (39). Zyka and Dolezal (288) described the microtitration of silver(1) and mercury(I1) with iron(11) in triethanolamine solutions. Other possibilities for iron(I1) titrations in this medium are discussed. New concentration cell or null-point measurements continue to be developed for trace and micro samples. Emmott (65) described a method for determination of chloride in lithium salts a t the part per billion level; as did Aleskovskif, Bardin, and Bystritskii (6) in potassium and sodium nitrates, lithium acetate, and potassium sulfate mixtures. A null-point method for the determination of silver(1) in the presence of excess copper(I1) or zinc(I1) is described by Ramachandran, Xatarajan, and Chellappa (207).
Rate Methods. Since this topic is reviewed elsewhere in this issue, only a few selected references of a wide variety of application will be discussed. Novoseiov, Muzykantova, and Ptitsyn (184) found t h a t potentiometric measurements of the rate of the Ce(1V)dihydrogenphosphite reaction were proportional to the silver(1) catalyst concentration through the range of 2 X 10-+-4 X 10-7M. Makarova (156) determined cholinesterase activity by potentiometrically following the conversion of butyrylcholine iodide. Gusinskaya (89) took advantage of the different rates of reaction of Ce(1V) , hln(VII), Cr(VI), and V(V) with methyl orange to effect individual determinations in the presence of the others. Tockstein (263) examined the rather complicated mechanism of the oxidation of naphthylamine by potential measurements very close t o completion where the kinetics become pseudo firstorder, in an inherently second-order reaction. In the miscellaneous, but interesting category, Alexander, Barclay, and McMillan (8)measured the potential of the working electrode with respect t o a reference electrode by interrupting the current to measure its potential decay in coulometric titrations of hydrochloric acid, acetic acid, and dichromate. The theory of this technique was later explained ( 7 ) . Despic and Popov-Sindjellic (50) determined copper(II1) in a titration with EDTA using the corrosion potential of a zinc or cadmium amalgam dropping electrode as the indicator. With cadmium amalgam, e.g., when the copper(I1) concentration is small, the electrode is completely polarized with respect to copper(I1) ; however, a t high copper(I1) concentrations the potential is determined by the oxidation of cadmium to cadmium(I1). Moebius (174) titrated combustible gases with oxygen gas. The electrode responded to oxygen partial pressures of 1 to 10-20 atm a t 800 to 1200' C. At the equivalence point, there is large increase in oxygen pressure and, hence, in potential. The electrode was fabricated from lutetium and scandium oxides in a zirconium oxide matrix (175). APPARATUS
This section deals with papers having a principal emphasis on instrumentation and apparatus. In addition to the reviews, the reader is referred t o manufacturer's literature and the annual Laboratory Guides (9, 10). Oehme and Wolf (187) reviewed pH equipment , Schrenker (235) reviewed measurements using glass electrodes and electronic instruments. Automatic potentiometric titrations were reviewed by Tacussel (253). Schulz (236) reviewed titration methods and equipment. Commercial
pH meters were reviewed by Price (200) and Aronson (14). Moore (178) presents practical methods for eliminating noise in pH measurements; primarily by using solution grounds. Schorcht (234, in a patent, describes another method t o avoid noise in high impedance potentiometric measurements, e.g., with glass electrodes. The potential difference between two electrodes is stored in a special capacitor which is alternately switched between the input of the amplifier and the electrodes. Jones (123) suggests applications of potential measurements in redox systems for process control. Schoedler (233) discussed the automatic control of pH in industrial processes. Blaedel and Laessig (25) reviewed continuous, automatic analyzers and described a system for the continuous titration of Fe(I1) with Ce(1V). These authors (24) also describe an instrumental system in which the flowing solution is constantly maintained a t the potentiometric end point by adjusting the flow rate of the EDTA titrant. Cu(II), Ca(II), Mg(II), and mixtures thereof were analyzed a t the 10-5~l level. The D M E or a mercury-coated tubular platinum electrode was used as the indicator. Gardels and Cornwell (74) described numerous automatic titrations with EDTA and redox systems. A commercial, automatic, continuous titrator is described in a patent by Boronkay (28). Miyake (178) described an automatic potentiometric titrator based on the principle of intermittent addition of titrant. The potential changes are measured after the addition of a 6' wen increment of titrant and are recorded stepwise. The titrant increments and time interval can be either preset or automatically controlled. It appears to this reviewer t h a t the instrument could easily be modified for use as a pH stat. Ehrhardt and Schorcht (61) describe an instrument for pH measurement, automatic titrations, and for use as a pH stat. It differs from conventional pH stats in t h a t either acid or base can be added automatically without manual switching. A patented automatic, potentiometric titrator is described by Dawe (47) based on the principle of proportional delivery of titrant. The speed of the motordriven buret is decreased as the rate of potential change increases. A similar instrument is described by Wuschke and Stewart (286) with the additional feature of automatic selection of forw,rd or back titrat,ion. A sensitivity of 10 fiV is claimed. A titrator with a derivative display is described in a patent by Lisy (150). This instrument is claimed to be useful for gaseous titrants. Several specialized potentiometric titrators have recently been developed. A titrator, accurate to 1 0 . 0 2 part per VOL 40, NO. 5, APRIL 1968
407 R
thousand, for use in the automatic determination of the salinity of sea water samples has been reported by Shimanova and Ponomarev (243). A design by Danielsson (46) to permit titrations of extremely slow acid-base reactions was effected by a timer circuit which connected a constant current source to the generator electrodes a t 30-min. intervals. A pH meter was used to measure the emf while the current was off. An apparatus for the automatic titration of titanium is described by Denton and Whitehead (48). The reduction of titanium in a cadmium reductor and titration by iron(II1) is automatically carried out in seven minutes with a standard deviation of 10.023%. The performance of automatic titrators was evaluated (167) for use in nonaqueous solvents (87)for comparison to manual titrations, and (149) for comparison of errors in an intermittent addition system to those using constant delivery rates. For the do-it-yourselfer, several relatively simple and/or inexpensive designs have been recently reported. Lama (143) described a multi-purpose recording pH meter which could be used as a pH stat and as a potentiometric titrator. A photoelectric relay system, operating from a commercial pH meter, was used to control the addition of titrant. A very simple and inexpensive titrator is described by Jennison and Clark (121). Titrimeters for student laboratory use were designed by Olsen (189) and Stock (264). Two solid-state pH meters were also described (111,
285). Riseman and Wall (218) described an apparatus for the determination of one ion in the presence of another ion by an ion-selective electrode system responsive t o each ion. The electrodes are coupled t o the measuring device so that the output is responsive only to the sought-for ion. A similar apparatus is described by Kremer and Vail (138) for the measurement of sulfide ion(PbS electrode) a t variable pH (glass electrode). Dahms (46) has extended this principle to the simultaneous measurement of Xa+, H +, K+, and C1- in blood. Schenk (230) described apparatus which overcomes the difficulties of titrating in liquid ammonia solvent. -4 water-jacketed cell for precise acid-base titrations (rt0.002 pH) was described by Perrin and Sayce (193). APPLICATIONS
Of the hundreds of articles using potentiometric end-point detection, approximately 60 have been selected for inclusion in this section. The selection is only a function of this reviewer's bias. Numerous applications with some special features have been cited in the pre-
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ANALYTICAL CHEMISTRY
ceding sections; other applications are reviewed elsewhere in this issue. The inorganic applications are grouped approximately by their positions in the periodic table. Inorganic. Deuterium has been determined (31) in water with a concentration cell of two gold-quinhydrone clectrodes separated by an agar bridge. The measured emf was almost a linear function of the DzO concentration in the test solution compartment. Potassium in potash was automatically titrated (103) with sodium tetraphenylborate using a mercury indicator electrode. The automatic titration with EGTA of magnesium and calcium in potash samples using the same electrode system is described (102). Magnesium and calcium were determined (21) with Complexon I11 using a platinum-carbon pair. Lead and zinc were determined (245') with disodium barium EDTA using the Pt/Fe(CN)6a-/Fe(CK)64- electrode. Mixtures of chloride, bromide, and iodide were automatically, and simultaneously, determined (94) with mercury (11) at the 2 X and lo-" levels, respectively, using a silver amalgam electrode. Titration with Fe(I1) in a phosphoric acid medium with an osmium catalyst and platinum electrode was used to determine iodate (271))periodate (272), iodine monochloride, and chloramine T (273). Bromide and iodide interfere whereas chloride, fluoride, nitrate, and sulfate do not. Chlorine dioxide and chlorine were simultaneously determined (61) by titration in KI-H2O2or H202media. I n the former case CIOz and C12are reduced to C1-, and in the latter case, C102 is reduced to C102- and C12 is reduced to C1-. Clog- was directly determined (127) in the presence of c103-, C102, and C1- by titration with C10- solutions using a platinum-SCE combination. Sulfate in potash samples was automatically determined (104) in 50y0 ethanol-water solutions by titration with lead(I1) using a lead amalgam electrode. Sulfur trioxide in oleum was determined (79) by titration with 86.35y0 aqueous sulfuric acid using an antimony indicator electrode and a glass or antimony concentration cell reference electrode. The end point reaction corresponds to H3S04+ HSO4- + 2H2S04. A platinum electrode was used (70) in the titration of K2SzOs, H2S05,and H202. The latter was titrated with KMn04 a t pH 1.8. The pH was increased to 4 with sodium acetate for the titration of H2SOs with Na&03, and KI-CuS04 was added for the final titration of K2S2Os with NazSzO3. A variation on the determination of K2Sz0swas reported (17 2 ) . The unknown K2S208solution was used
+
as the titrant for a standard solution of O.1M copper(1) chloride. Mixtures of nitrates and nitrites in 80% sulfuric acid gave separate inflections (78) using platinum-Hg/HgzSOd electrode combination in the titration with Ti(II1). Germanium(1V) was determined (38) in milligram quantities in a wide variety of matrices by potentiometric titration with potassium iodate. The method is based on the stabilization of the GeP04complex formed from the reduction by NaH2P02 in phosphoric acid. The formal oxidation potentials of some germanium(1V) compounds are also reported. Another method for the determination (276) of germanium(1V) compounds in 0.2 to 10 mg quantities was based on the distillation of GeC& into ammoniacal solution with addition of o-pyrocatechol t o form pyrocatecholgermanic acid which was subsequently titrated by sodium hydroxide. Antimony(V) was determined (181) in 20-200 mg quantities using a platinum electrode by titration with Cr(11). V(II), Ti(III), or thiourea. Best results were reported for the Cr(I1) ~ error). Antititrations ( 4 ~ 0 . 4 7rel. iron(I1) , mony (111), arsenic(III), tin(II), and iodide in concentrations of 0.2-2.0 mg/ml were successfully titrated (170) in glacial acetic acid with cobalt(111) solutions prepared from the anodic dissolution of cobalt in acetic acid. A method for the determination of iron(I1) and iron(II1) in mixtures was reported (282). Iron(I1) was directly tit,rated in 2-100 mg amounts with K3Fe(CN)6 in concentrated hydrochloric acid. Iron(I1) was determined by prior reduction with stannous chloride. The tris-oxalato complexes of iron(II1) and chromium(II1) were titrated (202) with vanadium(V) in 3;M sulfuric acid with a platinum-SCE combination. Two of the iron(II1) oxalate groups were individually titrated, but the two chromium(I1) oxalate groups were titrated a t the same potential. Cerium(1V) and iron(II1) were successively determined (128) in 4il.I sulfuric acid by titration with vanadium (11). Few interferences were observed. Vanadium(1V) was determined (129) by the back titration with mercury(I1) of the excess EDTA added. Cobalt(II1) was determined (222) by titration with KaFe(CX), using a platinum-tungsten bimetallic electrode pair. Cobalt(I1) was similarly determined (262) by titration with K3Fe(CN)6 in ammoniacal medium using a platinum-SCE pair. Palladium(II1) in catalysts was titrated directly (246) with solutions of potassium iodide using a palladium-SCE combination. Osmium tetroxide was determined (229) by prior reduction to osmium(II1) in a bismuth reductor
column with subsequent titration by cerium(1V) , manganese(VII), or lead(IV) using a platinum-SCE combination. Erbium(II1) was titrated directly (277) with ammonium oxalate using a platinum-SCE combination. The reaction was slow at first, but was sufficiently rapid later in the titration for a sharp end point. Uranium in high purity uranium metal was assayed (57) by back titration of the excess potassium dichromate added to uraiiium(1V) solutions with iron(I1). A relative accuracy and precision of =t0.005% was claimed. A similar analysis was reported (201) for uranium(1V) by direct titration t o uranium(1V) with potassium dichromate in phosphoric acid. The relative standard deviation was 3=0.003OjC. Plutonium is determined by oxidation t o plutonium(V1) using silver(I1) oxide, addition of a measured excess of iron(II), and subsequent back titration by potassium dichromate using polarized gold electrodes (53) and by back titration with cerium(1V) using platinum-SCE electrodes (168, 169). The relative standard deviations for milligram amounts was +0.1 t o =t0.2’%. h similar analysis by titration with potassium dichromate using constant current potentiometry was reported (195) t o give a standard deviation of 5 0.04%.
Organic. These applications are grouped in order of acid, base, redox, precipitate, or complex formation reaction functions. Sodium methoxide was used as the titrant for the titration of successive protons of dicarboxylic acids (116) in pyridine or acetone media, for bis(ary1and alky1amine)tetrabromotellurium(IV) adducts (113) in ethyl acetate or dimethylformamide using a n antimony electrode, for phosphinic acids (115) in methanol, dimethylsulfoxide, or dimethylformamide using a glass electrode, and for phenylhydrazones or 2,4dinitrophenylhydrazones (114), in pyridine using an antimony electrode. Tetrabutylammonium hydroxide was used as the titrant for the determination of hydroxamic acids (251) in nine different solvents with three different electrode systems, for naphthalenecarboxylic acids (140) in isopropanol, and for nitroguanadine (4) in acetone-dimethylformamide using a glass electrode. Tetraethylammonium hydroxide in benzene-methanol was also used in the latter application. p-Nitro alcohols were determined ( 5 ) in acetone using tetrabutyl, ethyl, or methyl ammonium hydroxides. 8-Hydroxyquinoline and derivatives were determined (217) in pyridine by titration of the phenolic proton with sodium hydroxide in methanolic solution. Sulfate and sulfonic acid derivatives could not be determined by this
method. Poly(methacry1ic acid) was determined (283) using barium hydroxide with a glass electrode. Terephthalic and p-toluic acids were simultaneously determined (267) in dimethylformamide with aqueous potassium hydroxide using a glass electrode. Acetyl chloride and acetic anhydride were determined (257); the former in pyridine with silver acetate in the presence of the latter and acetic acid. The acetic anhydride was titrated with aniline in acetic acid. A novel method was reported (73) t o determine the pK values of the phenolic proton of aminophenols by cyanoethylation of the amino groups with subsequent titration by base. Carbonyl compounds were determined (125) in acetic acid by addition of NH?OH.HOAc. After the oximation, the excess “,OH .HOrlc mas titrated with perchloric acid. The hydrochlorides of chlorotetracycline, oxytetracycline, and tetracycline were determined (64) in acetic anhydride by titration with perchloric acid using glass-silver chloride electrodes. Hydrochlorides and hydrogen maleates of five phenothiazine derivatives (192) and 1,4-butanediol dicarbamate (106) were similarly determined in dioxaneacetic acid solvents. Mixtures of amino acids were determined (139) in acetonitrile-acetic solvent with perchloric acid in 2-butanone using a glass electrode. E-Caprolactam was titrated (3) as a base in acetic anhydride, or acetic acid with excess acetic anhydride present by perchloric acid solutions in acetic anhydride. 0-Phthalimide selenoxide is similarly determined (253) in acetic anhydride with perchloric acid-dioxane. Heterocyclic bases and their N-oxides were determined (133) by titration with perchloric acid. Only acetic acid can be used as solvent for the base and its S-oxide, while acetic acid can be used for the determination of 2,6-lutidine N-oxide in the presence of other N oxides. Phosphatides were analyzed (247) by titration with perchloric acid before and after treatment with acetic anhydride. Phosphatides with a zwitterion structure were titrated with perchloric acid directly. The phosphatides containing a n amino group were titrated separately as amides after treatment with acetic anhydride. Mixtures of azo- and hydrazobenzenes were analyzed (182) by redox titrations using a platinum-calomel combination. Azobenzene was titrated with titanium(111) under nitrogen; hydrazobenzene was determined with potassium permanganate. hlandelic acid and zirconium mandelates were titrated (164) in milligram quantities in 2.11 sulfuric acid with vanadate solutions. Organic compounds containing active hydroxyl and amino groups were titrated (165) with standard solutions of
beiizenediazonium or 4-nitrobenzenediazonium chlorides. Five compounds in addition t o resorcinol and 2-naphthol were determined automatically by this method. Potassium xanthate waq determined (126) by titration with mercury(11) acetate using a mercury electrode. ACKNOWLEDGMENT
The author expresses his appreciation to the Department of Chemistry, Duke University, for the use of its facilities, t o the typists, and especially t o the Chemistry librarians, Carolyn Moore and H. Tucker Marshall, without whom this work would not have been possible, LITERATURE CITED
( 1 ) Agasyan, L. B., Xikolaeva, E. R.,
Agasyan, P. K., Zh. Anal. Khim., 21,
1470 (1966). (2) Agin, D.,’Holtzman, D., Nature, 211, 1194 (1966). (3) Apmov, V. K., Kolokolov, B. N., Gel fer, S.hl., Zh. Anal. Khim.., 21., 729 (1966). (4) Aksenenko, V. hf., Aksenenko, E. G., Gromova, E. N., Zdvodsk. Lab., 31, 1191 ( 196.51.
( 5 ) Ibid., 32, 19 (1966). ( 6 ) AleskovskiI, V. B., Bardin. V. V.. BystritskiI, A. L., Ibid., p 148. ’ (7) Alexander, W. A., Barclay, D. J., J . Electroanal. Chem., 13, 181 (1967). (8) Alexander, W. A., Barclay, D. J., hlchlillan, A., Analyst, 90, 504 (1965). (9) A N ~ LCHEM., . 38 (8), pt. 2 (1966). (10) Ibzd., 39 (9) (1967). (11) Apte, V. P.,. Dhaneshwar, R. G., Talanta, 13, 1 5 9 ~(1966). (12) Ariel, 1. &I., Kirowa-Eisner, E., J . Electroanal. Chem., 10, 319 (1965). (13) Ibid., 13, 90 (1967). (14) Aronson, M., Instr. Control Systems, 38 (8), 81 (1965). (15) Banick, W. X, Jr., Encycl. Znd. Chem. Anal., 3 , 200 (1966). (16) Bates, R. G., Ibid., p 146. (17) Bates, R. G., Ed., National Bureau of Standards, Technical Note No. 400, 1966. (18) Ibid.. No. 423. 1967. (19) Bau;, J. A., ’Bricker, C. E., ANAL. CHEM.,37, 1461 (1965). (20) Belinskaya, F. A., Materova, E. A.. Severov, B. A . , Grinberg, G. P.,’Ionnyi Obmen, Leningr. Gos. Univ., 1965, 13. (21) Berkovich, M. T., Sirina, A. M., Tr. Ural’sk. lVauchn.-Issled. Khim. Inst., 1964 38; CAI 64, 2733b (1966). (22) Bfshop, E., Proc. SAC Conf., Nottingham, Engl., 1965, 291. (23) Ibid., p 416. (24) Blaedel, W. J., Laessig, R. H., ANAL. CHEM.,38, 186 (1966). (25) Blaedel, W. J., Laessig, R. H., Advan. Anal. Chem. Instr., 5, 69 (1966). (26) Boksay, Z., Bouquet, G., Csakvari, B., Acta. Chim. Acad. Sci. Hung., 46, 151 (1965). (27) Bontron, J. C., Compt. Rend., 261, 417 (19653. (28) Boronkay, A. D., U. S. Patent 3,275,533 (Sept. 27, 1966). (29) Breant, hl., Nguyen-Van-Kiet, Bull. SOC.Chim. France, 1965,3638. (30) Buchanan, Jr., E. B., Seago, J. L., J . Electrochem. SOC.,114, ,595 (1967). (31) Bucur, R. V., Tinis, L., Abh. Deut. Akad. Wiss. Berlin, K1. Chem., Geol. Biol., 1964, 485; CA, 66, 51916~. (32) Butcher, J., Fernando, Q., Anal. Chim. Acta, 36, 65 (1966). (33) Butcher, J., Fernando, Q., J . Chem. Educ., 43, 546 (1966). VOL 40, NO. 5, APRIL 1968
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(34) Camman, K., 2. Anal. Chem., 216, 287 (1966). (35) Camman, K., Fortuchr. Chem. Forsch., 8, 222 (1967). (36) Chauchard. J.. Gauthier. J..’ Bull. ‘ SOC.Chim. France; 1966,2635. (37) Chem. Eng. News, 44 (22), 50 (1966). (38) Cheng, K. L., Anal. Chim. Acta, 35, 293 (1966). (39) Close, P. T., Hornyak, E. J., Baak, T., Tillman, J. F., Microchem. J., 10,334 (1966). (40) Cohen, S. R., ANAL. CHEM.,38, 158 (1966). (41) Copello, M. A., de Dorfman, E. A., Anales SOC.Cient. Arg., 181, 33 (1966). (42) Covington, A. K., Dobson, J. V., Lord Wvnne-Jones. 0. 0.. Electrochim. Acta, 12; 513 (1967). (43) Ibid., p 525. (44) Csakvari, B., Dobos, S., PekariKerepesi, hl., ilcta Chim. Acad. Sci. Hung., 48, 1 (1966). (45) Dahms, H., Clin. Chem., 13, 437 (1967). (46) Danielsson, I., Kem. Teollisuus, 23, 1081 (1966). (47) Dawe, G. A., U. S. Patent3,246,952 (April 19, 1966). (48) Denton, C. L., Whitehead, J., Analyst, 91, 224 (1966). (49) De Rossi, M., Pecci, G., Scrosati, B., Ric. Sci., 37, 342 (1967). (50) Despic, A. R., Popov-Sindjellic, K. I., J . Electroanal. Chem., 12, 347 (1966). (51) Dobryshin, K. D., Flis, I. E., Vorobev. I. hL. Kokushkina. V. A.. Zh. Analit. Khim., 21, 752 (1966j. (52) Douheret, G., Bull. SOC. Chim. France, 1966, 3341. (53) Drummond, J. L., Grant, R. A., Il’alanto,13, 477 (1966). (54) Dubois. J. E.. Lacaze, P. C., Anal. C‘him. Acta. 33.403 (1965). (55) Ibid., p i03.’ (56) Ibid., p 602. (57) lluckitt, J. A., Goode, G. C., U.K . ~
~I
At. Energy Auth., Prod. Group, PG Rept.
720(S), 1966. (58) I h r s t , It. A., J . Chem. Educ., 43, 437 (1966). (59) Ibid., 44, 175 (1967). (60) Dutz, H., Glastech. Ber., 39, 139 (1966). (61) Ehrhardt, J., Schorcht, A,, Jena Rev., Spec. Issue 1963, 35. (62) Eisenman, G., Ed., “Glass Electrodes for Hydrogen and Other Cations,” Marcel Dekker, New York, 1967. (63) Eisenman, G., Bates, R. G., Mattock, G., Friedman, S. M. “The Glass Electrode,” Interscience, kew York, 1966. (64) Ellert, H., Ceglarski, R., Regosz, A,, Farm. Polska, 22, 185 (1966). (65) Emmott, P., Analyst, 90, 482 (1968). (66) Every, It. L., Banks, W. P., Electrochem. Technol., 4, 275 (1966). (67) Flis, E. I., Shirokova, V. N., Donskaya, E. V., Tr. Leningr. Tekhnol. Inst. Tsellyu1ozn.-Bumazhn.Prom. No. 13, 75 (1964). (68) Foerland, T., Oestvold, T., Acta Chem. Scand., 20, 2086 (1966). (69) ‘Foerland, T., Thulin, L. V., Ibid., 21, 1121 (1967). (70) Fomina, T. V., Flis, I. E., Dymarchuk, N. P., Tr. Leningr. Tekhnol. Inst. Tsellvu1ozn.-Bumazhn.Prom. No. 16, 88 (1965). (71) Frant, M. S., Ross, Jr., J. W., Science, 154. 1553 f 1966). (72) Freddi,‘R., Bombi, G. G., Fiorani, M., 2. Anal. Chem., 222,369 (1966). (73) Friedman, M., Biochem. Biophys. Res. Commun., 23, 626 (1966). (74) Gardels, hI. C., Cornwell, J. C., A N A L . CHEY..38. 774 (1966). (75) Gerchman; L.‘L., Rechnitz, G. A., Z. Anal. Chem., 230,265 (1967). 410 R
ANALYTICAL CHEMISTRY
(76) Geyer, R., Peker, J., Wiss. Z . Tech.
Hochsch. Chem. Leuna-Merseburg, 8, 15
(1966). (77) Geyer, R., Syring, W., Z . Chem., 6, 92 (1966). (78) Giuffre, L. Losio, E., Castoldi, A,, Chim. Ind. ( d i l a n ) ,48, 721 (1966). (79) Ibid., p 958. ( 8 0 ) Glauser, S. C., Ifkovits, E., Glauser, E. M., Sevy, R. W., Proc. SOC.Exptl. Biol. Med., 124, 131 (1967). (81) Goldman, J. A,, J . Electroanal. Chem., 11, 255 (1966). (82) Ibid., p 416. (83) Gordievskif, A. V., Filippov, E. L., Shterman, V. S., Trizno, V. V., Zh. Analit. Khim., 20, 1164 (1965). (84) GordievskiI, A. V., Filippov, E. L., Shterman, V. S., Elektrokhimiya, 3, 500 (19671. (85,-lbi&, p 642. (86) Gregor, H. P., Schonhorn, H., U. S. Patent 3,258,414 (June 28, 1966). (87) Greuter., E.., Z . Anal. Chem.. 222. 224 ‘ (i966). (88) Gross, D. J., Murray, R. W., KirkI
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Othmer Encycl. Chem. Technol., Wnd Ed.,
7, 726 (1965). (89) Gusinskava, S. A,, Zh. Analit. Khim., 2i, 1462 (1966’). ’ f90) Hanvard. T.. ChaDman. K. M..‘ J . ‘ ElectrGihem.’ Sol., 113; 961 (1966). (91) Hahn, F. L., “pH und Potentiometrische Titrierungen,” (hlethoden der Analyse in der Chemie) Vol. 3, Akad. Verlamaes. Frankfurtlhlain. 1964. (92) Hakoila, E., Suomen Kemistilehti, B II
39.I 96 - - f19661. \ - - - - I
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(93j Hannema, U., den Boef, G., Anal. Chim. Acta, 39, 167 (1967). (94) Harzdorf. C., 2. Anal. Chem.,. 215,. 246 (1965) f9B) Havir. J.. Collection Czech. Chem. ‘ Commun:, 31; 130 (1967). (96) Headridge, J. B., Pierce, T. B., Anderson, D. M. W., Ann. Rept. Progr. Chem. (Chem. SOC. London), .. 62,. 511 (1965). (97) Helbig, W., Chem. Tech. (Berlin), 18, 344 (1966). (98) Helbig, W., 2. Anal. Chem., 216, 280 (1966). (99) Henderson, R. M.,J . Appl. Phys., 22, 1179 (1967). (1001 Herlem. M.. Bull. SOC. Chim. France, 1965, 3329. (101) Herman, M., Sulcek, Z., Zyka, J., Collection Czech. Chem. Commun., 31, 2005 (1966). (102) Hessler, W., Bergakademia, 17, 478 (1965). (103) Ibid., 18, 303 (1966). (104) Hessler, W., Adam, G., Trapp, W., Ibid., 19, 33 (1967). (105) Hilton, C. L., Encycl. Ind. Chem. Anal., 1, 634 (1966). (106) Hippe, Z., Krzyzanowska, T., Chem. Anal. (Warsaw), 10, 179 (1965). (107) Hladik, J., Saunier, M., Morand, G., C. R. Acad. Sci. Paris, Ser. C, 263, 357 (1966). (108) Hladky, Z., 2. Chem., 5, 424 (1965). (109) Hoare, J. P., J . Electroanal. Chem., 12, 260 (1966). (110) Ijsseling, F. P., van Dalen, E., Anal. Chim. Acta, 36, 166 (1966). (111) Jacobsen, J. K., ANAL. CHEM.,38, 1975 (1966). (112) Jakuszewski, B., Badecka-Jedrzejewska, J., Roczniki Chem., 39, 907 (1965). (113) Jasinski, T., Kokot, Z., Chem. Anal. ‘ (Warsaw), 11, 967 (1966). . (114) Jasinski, T., Kopciowski, K., Zeszutu Nauk Mat. Fiz. Chem. Wvzsza S z k d d Pedagog. Gdansk, 3, 77 (1963); CA, 64, 5760d (1966). (115) Jasinski, T., Modro, A,, Modro, T., Chem. Anal. (Warsaw), 10, 929 (1965). ,
~
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16) Jasinski, T., Smagowski, H., Ibid., p 1321. 17) Jasinski, T., Smagowski, H., Zeszyty Nauk Mat. Fiz. Chem., Wyzsza Szkoh Pedagog. Gdansk, 5, 53 (1965); CA 65, 17687e (1966). 18) Jasinski, T., Smagowski, H., Korewa, R., Chem. Anal. (Warsaw),11, 74.5 I\ -1 -966). --,. 19, - - Jasinski, - - - - , T., Stefaniuk, K., Ibid., 10, 983 (1Y65). 20) Jenkins, D. A., Latham, J. L., J . Chem. Educ.. 43. 82 (1966). (121) Jennison, W:, Clark, hf. L., Analyst, 91, 598 (1966). (122) Johannesen, B., Aslaksen, B., Thom, E., Medd. Norsk Farm. Selsk, 28, 369 (1966). (123) Jones. R. H.. Instr. SOC.Am. J.. 13 . (11), 40 (1966). ‘ (124) Kalbus, L. H., Kalbus, G. E., Ana/. Chim. Acta, 39, 335 (1967). 125) Kazarinov, M. O., Dzyuba, N. P., Med. Prom. SSSR, 20, 50 (1966). 126) Kekedy, L., Makkay, F., Studia Univ. Babes-Bolyai, Ser. Chem., 9, 55 (1964); CA, 64, 1357e (1966). 127) Kepinski, J., Blaszkiewicz, G., Talanta, 13, 357 (1966). 128) Ketova, L. A., Materialy Nauchn. I
Konf., Permsk, Med. Inst., Sb., Perm, 1964.71; CA 65. 11333d f 1966). 129j Khaiifa, H.,’ El-Sirafy, A.,’Z. Anal. Chem., 227, 109 (1967). 130) King, J. A., Mukherji, A. K., Naturwissenschaften, 53, 702 (1966). 131) Kirowa-Eisner. E., Ariel, M.,J . Electroanal. Chem.,’ 12, 286 (1966). ‘
132) Kolodney, M., Minushkin, B., Steinmetz, H., Electrochcm. Technol., 3, 244 (1965). 133) Kondratov, V. K., Novikov, E. G., Zh. Anal. Khim., 22, 587 (1967). 134) Kono, X., Ikegami, A., Biopolymers, 4, 823 (1966). 135) Konrad, K. K., Proc. Satl. Anal. Instr. Symp., loth, Sun Francisco, 1964, 35. (136) Kotkowski, S., Lassocinska, A., Chem. Anal. (Warsaw), 11, 789 (1966). (137) Kratochvil, B., Zatko, I). A., Markuszewski, R., ANAL.CHEM.,38,770 (1966). (138) Kremer, V. A., Vail, E. I., U.S.S.R. Patent 180,398 (March 21, 1966). (139) Kreshkov, A. P., Aldarova, N. Sh., Turovtseva. G. V.. Dokl. Akad. iVauk SSSR, 169,’1093(1966). 40) Kreshokov, A. P., Bykova, L. N., Kazaryan, N. A., Rubtsova, E. S., Izv. Vysshikh Uchebn. Zavedenii, Khim. i Khim. Tekhnol., 9, 72 (1966); CA, 65, 8009h (1966). 41) Kreshkov, A. P., Yarovenko, A. N., hlilaev, S. M.,Aldarova, N. Sh., Zh. Analit. Khim., 21, 34 (1966). 42) Kryukov, P. A,, Perkovets, V. D., Starostina, L. I., Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. iVauk, 1966,29. 43) Lanza. P.. J . Electroanal. Chem... 13.. 67(1967).’ ’ (144) Lengyel, B., Csakvari, B., Acta Chim. Acad. Sci. Hung., 50, 119 (1966). (145) Lengyel, B., Csakvari, B., Toperczer, J., Ibid., 45, 177 (1965). (146) Leonard, L. B., Watanabe, H., U. S. Patent 3,264,205 (Aug. 2, 1966). (147) Light, T. S., Fletcher, K. S., ANAL. CHEM.,39, 70 (1967): (148) Lingane, J. J., Ibzd., p. 881. (149) Linnet, K.,Radiometer News, No. 6, 7. I196.5l \----,-
(150) Lisy, J. hl., Czech. Patent 117,383 (Jan. 15, 1966). (151) Liteanu, C., Mioscu, M., Rev. Roumaine Chim., 10, 903 (1965). (152) Luca, C., Magearu, V., Popa, G., J. Electroanal. Chem., 1 2 , 45 (1966). (153) Luneva, V. S., Burdenyuk, L. N., Zashchitn. Metal. Oksidnye Pokrytiya,
Korroziya Metal. i Issled. v Obl. Elektrokhim. Akad. Nauk SSSR, Otd. Obshch. i Tekhn. Khim., Sb. Statei 1965, 337; CA, 65, 3632c (1966). 54) McClure, J. E., Rechnitz, G. A,, ANAL.CHEM.,38, 136 (1966).
55) hlagearu, V., Luca, C., Teodorescu, M, J . Electroanal. Chem., 12, 148 (19fi6). 56j-&karova, V. R., Nauchn. Osnovy Proizv. Vaktsin i Syvorotok, Sb. (Moscow: Meditsina), 1965, 261; CA, 65, 18913b (1966). (157) hlanecke, G., Foerster, H. J., Panoch, H. J., 2. Anal. Chem., 216, 285 (1966). (158) Xlarple, L. W., ANAL. CHEM.,39, 844 (1967). (159) hlarple, L. W., J . Chem. Eng. Data, 12, 437 (1967). (160) hlarple, L. W., Scheppers, G. J., ANAL.CHEM.,38, 553 (1966). (161) AIaterova, E. A., Grinberg, G. P., Ionnyi Obmen, Leningr. Gos. Univ., 1965, 99. (162) ?laterova, E. A., Grinberg, G. P., Panicheva, S. E., Ibid., p 89. (163) Materova, E. A., Rozhanskaya, T. M., Furman, T. M., Ibid., p 78. (164) Alathur, D. L., Bhansali, G. R., Rao, S. P., J . Electroanal. Chem., 15, 315 (1967). (163) Matrka, hl., Spevak, A., Verisova, E., Chem. Listy, 61, 532 (1967). (166) Mattock, G., Chimia, 21, 209 (1967). (167) hledwick, T., Kirschner, E., J . Pharm. Sci., 55, 1296 (1966). (168) Nilner, G. W. C., Wood! A. J., Cassie, G. E., NASA Accession No. N66.14166., ReDt. . No. AERE-R-49795 (1965). (169) llilner, G. W. C., Wood, A. J., Weldrick, G., Phillips, G., Analyst, 92, 239 (1967). (170) RIinczewski, J., Pszonicka, M., Chem. Anal. (Warsaw), 10, 1357 (1965). (171) Mishin, V. Ya., Parpiev, N. A., Uzb. Khim. Zh., 11, 58 (1967). (172) Ilisra, G. J., Tandon, J. P., Chemist Analyst, 55, 79 (1966). (173) Rliyake, S., Talanta, 13, 1253 (1966). (174) ?*Ioebius, H. H.. Z . Phvsik. Chem., 231, 209 (1966). ' (175) hloebius, H. H., Proeve, G., 2. Chmn.. Chem., 55,. 431 (196A). (1965). (176) ( 1 f 6 j Jlonien, 3foden, H., Specker, H., Z . Anal. Chem., 224, 3--
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Izv. Akad. Nauk Kaz. SSR, Ser. Khim. Xauk, 15, 15 (1965). (250) Ibid., 16, 87 (1966). (251) Stamey, Jr., T. W., Christian, R., Talanta, 13, 144 (1966). (252) Staroscik, Ii., Siaglo, H., Chem. Anal. (Warsaw), 10, 265 (1965). (253) Stefanac, Z., Tomaskovic, M., Bull. Sci. Conseil Acad. RSF Yougoslavie, 10, 317 (1965); CA, 65, 4640d (1966). (254) Stock, J. T., J . Chem. Educ.. 43.425 I
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Vysoka Skola, Chem. Technol., Pardubice, 1965, 27. (264) Tokiwa, F., Ohki, K., J . Phys. Chem., 70, 3437 (1966). (265) Townsing, P. C., Posner, A. M., Quirk, J. P., Anal. Chim. Acta, 38, 464
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41 1 R
(268) Vandenbalck, J. L., Ing. Chimiste, 48, 12 (1966). (269) Van RysseIberghe, P., Defay, R., Ibl, N. Lange, E., Levart, E., hlilaszo, G., Vaiensi, G., Electrochim. Acta, 12, 748 (1967). (270) Villarreal, E., Rw. SOC.Quim. Mez., 8 , 201 (1964). (271) Vulterin, J., Collection Czech. Chem. Commun., 31, 2501 (1966). (272) Ibid., p 3529. (273) Ibid., p 4662. (274) Waligora, B., Paluch, hf., Chem. Bnal. (Warsaw),10, 693 (1965).
(275) Waser, J., J . Chem. Educ., 44, 274 (1967). (276) Wasowicz, S., Chem. Anal. (Warsaw), 10,933 (1965). (277) Wawrzyczek, W., Benedict, A., Jagosz, R., 2. Anal. Chem., 214, 258 (1965). (278) Whiteker, R. A., Murphy, D. W., ANAL.CHEM.,39, 230 (1967). (279) Whiting, G. C., Chem. Ind. (London), 1966, 1030. (280) Wilson, R. F., Fennell, P. M., Texas J . Sci., 17, 219 (1965). (281) Wimer, D. C., Encycl. Ind. Chem. Anal., 1 , 30 (1966).
(282) Wisniewski, W., Basinka, H., Chem. Anal. (Warsaw).12. 99 (19fi7). (283) Wojtczak, Z . ~ ~ b t Z . , ' ~ $37 & (1965). (284) Woodhead, M., Paabo, M., Robinson, R. A., Bates, R. G., P;NAL:CHEM., 37, 1291 (1965). (285) Wunderer, P., Dechema Momgraph. 54, 311 (1965). (286) $uschke, E. E., Stewart, R. B., At. Energy Can. Lid., Whiteshell iVucl. Rea. Estab. AECL-2262 (1965). (287) Zatko, D. A., Kratochvil, B., ANAL. CHEM.,37, 1560 (1965). (288) Zyka, J., D o l e d , J., Microchem. J., 10, 554 (1966).
Volumetric and Gravimetric Analytical Methods for Organic Compounds W a l t e r T. Smith, Jr., William F. W a g n e r , and John Lexington, Ky. 40506
T
methods discussed in this review have been selected from the literature which has become available to the reviewers from November 1965 through November 1967. HE BXALYTICAL
DETERMINATION OF ELEMENTS
A series of articles reviews the present status of organic elemental analysis (92), determination of carbon and hydrogen (5, 46), halogen and sulfur ( I % ) , nitrogen (82), and flask combustion methods (88). A review covering the mineralization of ferrocenes for the determination of iron, determination of halogens in organometallic compounds, and a mineralization with strong acids with the addition of oxidizing agents contains 28 references (50). Combustion Methods. The design and operation of many types of combustion apparatus for the determination of carbon, hydrogen, nitrogen, oxygen, and the halogens are described (61)
.
A technique for handling lowmelting
samples in oxygen-flask combustions was developed, The sample is wrapped in about 200 mg of surgical grade cotton which serves as a wick to prevent the melt from falling into the absorption liquid (96). I n the wet combustion of organic compounds containing C, H, and C, H , and 0, a study was made of the dependence of the oxidation by a KI0,H2S04 mixture on the concentration of acid and temperature. The oxidizing power was highest a t 97% HzS04 and 225' C, the conditions under which the HI03 formed in the mixture begins t o decompose (119). A patent for elemental analysis is based on treating the organic substances 412 R
ANALYTICAL CHEMISTRY
M. Patterson, Department o f Chemistry, University o f Kentucky,
with oxygen, t h a t has been activated by high-frequency electrical discharge, for the determination of elements other than oxygen. Oxygen is determined by treating the sample with similarly activated hydrogen (41). Carbon and Hydrogen. A wet combustion method was applied to the determination of carbon in aqueous extracts of weathered coal and solid residues from coal. Purified oxygen was bubbled through the aqueous solution kept a t 150-160° C ; the gaseous products s e r e passed over a chromium catalyst a t 700-750' and carried through a series of absorption tubes to absorb water, chlorine, and hydrogen chloride. Pure carbon dioxide was collected on ascarite and determined gravimetrically (71). -4method was developed for the direct determination of hydrogen in sulfur by pyrolysis in sealed tubes a t 500" C for six hours. After being cooled, the ampule is placed in a flask containing 20 ml of 0.1N iodine solution. The H2S from the sample reacts with the iodine, the excess of which is titrated with 0.1N sodium thiosulfate. A range of 0.01 t o O.OOlCr, of hydrogen in a onegram sample may be determined (14). Halogens. Chlorine in tolylene diisocyanate was determined by hydrolysis with metallic sodium in butanol, followed by precipitation and wreighing as AgC1. Standard deviation was approximately 3% for chlorine contents of 0.005 to 0.1%. The lower limit of determination was 0.003% (93).
Reduction by sodium was used for the determination of halides in Vinylite resins and in organometallic compounds. The sample was treated with metallic sodium in a mixed dioxane-ethylcellu-
lose solvent. After the addition of water the halide was determined by the Volhard method. Absolute deviation was $0.56y0 for Vinylite resins and so.37y0 for the organometallic compounds (99). Liquid samples were analyzed for chlorine by placing the sample (40-50 mg) on a wick and adding 20-30 mg of sucrose, naphthalene, EDTA, or potassium hydrogen phthalate, followed by ignition of the wick. The combustion products were absorbed in water, and the solution was titrated potentiometrically with 0.1.V Hg(N03)2with an error of 1%. EDTA gave the best results in the combustion (65). -4 solution of biphenyl-sodium-dimethoxyethane complex was used t o decompose organic fluorine compounds. The fluoride ion was titrated with 0.04N Th(K03)d (141). N-Bromosuccinimide oxidizes organic iodo compounds t o iodoso derivatives, rhich are titrated with ascorbic acid or treated with KI to liberate iodine t h a t is titrated with Xa2S20a. Obstinate cases are treated with zinc t o produce iodide ion which is titrated with standard N bromosuccinimide (116). Metals. A method was developed for the determination of aluminum in organic compounds containing silicon and phosphorus after their decomposition by fusion with NazOz in a n oxygen atmosphere in a calorimetric bomb. An excess of a standard solution of E D T A was added to the solution of aluminum ion obtained from the fusion, and the excess was titrated with 0.01M CuSOa (130). Aluminurn in poly alumino-siloxanes was determined after decomposition in a mixture of acetone and hydrochloric acid. Aluminum was titrated by a
chelatometric procedure using zinc sulfate as the back titrant. Relative error ranged from -0.15y0 to -1.62y0 (87). Iron in ferrocene and its silicon-organic derivatives are decomposed in a mixture of CC14, concentrated HCl, and (NH4)2S208. The iron is titrated iodometrically or with EDTA by standard procedures, giving an absolute error of -0.20 t o +o.25y0 for iron content ranging from 18.05 t o 42.93% (86). ilfter combustion in an oxygen flask and absorption in nitric acid solution, mercury may be determined gravimetrically by precipitating and weighing as a complex cobalt hexammine thiosulfato-mercury salt (27). After mineralization the tin in organotin compounds may be determined by adding a known amount of EDTA and back titrating with copper(I1) ion, using any of several synthetic heterocyclic azo dyes as indicators. The maximum error reported was +0.1180j, Sn (22). Nitrogen. Jurecek a n d coworkers (51,58,59) have extended studies on the use of chromic acid oxidation of organic compounds in the determination of nitrogen. Oxidation numbers were also determined by titration of excess chromic acid after the digestion. The nitrogen evolved from the hydrazine group in semicarbazones was measured in an azotometer. The amine nitrogen was determined by distillation of ammonia from the solution. The procedure was also applied to Schiff bases from which ammonia was evolved. Compounds containing nitro groups were reduced with Devarda alloy to ammonia. Deviations were in the limits +o,3y0 (59). The method was applied to the simultaneous determination of nitro, nitroso, and secondary or tertiary amino groups (51). Organic substances containing the N-N group in a ring are oxidized to nitrogen, the volume of which is measured. Compounds analyzed were derivatives of pyrazolone, benzotriazole, and 1,2,4-triazine. The third nitrogen in the benzotriazoles and triazines is converted to ammonia which can be determined by distillation methods (58). The relative merits of the Dumas and Kjeldahl methods for the determination of nitrogen in soils are discussed. Modifications of the Kjeldahl method for completeness of digestion and inclusion of nitrates and nitrites are described in detail. Three macro methods and one semimicro version are recommended (15).
Oxygen. A modified method for the determination of organic oxygen in coal is based on a n investigation of published methods. The sample is pyrolyzed a t 1120' C under carefully controlled conditions in the presence of nitrogen gas as a carrier. T h e products are passed over charcoal to complete the reduction t o CO. After
removal of sulfur compounds, the CO is oxidized t o C02over modified Schuetze reagent and determined gravimetrically
n
=
no. of atoms of same functional element in the group (e.g., for-COOR, n for 0 = 2).
(19).
Phosphorus. Phosphorus in organophosphorus compounds was converted to phosphate by fusion with Na202 in a steel bomb, or in a calorimetric bomb, or wet oxidation by a mixture of concentrated H2S04 and "03. T h e phosphate was converted to ammonium molybdophosphate which was determined quantitatively by conventional gravimetric and volumetric procedures (74). A similar combustion by Na202gr oxygen in a calorimeter was reported for the conversion of phosphorus to phosphate which was precipitated as NH4ZnPO4 followed by a titration of the zinc ion with EDTA (20). Toxic organophosphorus compounds are separated from natural and waste waters by extraction into diethyl ether or adsorption on activated carbon. The compounds are converted to phosphate by ignition with a mixture of 4: 1 ZnONi2C03. Phosphate is determined by the molybdate method (70). A patent describes the determination of trivalent phosphorus in phosphites and phosphonites. The sample is dissolved in absolute benzene and titrated with 0.5N dioxane dibromide t o the appearance of a lemon-yellow color (124). Selenium. A procedure for the determination of selenium is applicable for organoselenium compounds. The sample is refluxed carefully with a mixture of KC104 in concentrated H2S04. T h e solution is diluted, treated with HC1 and phenol and titrated with a standard solution of Na2S203(56). iifter combustion in an oxygen flask, selenium is determined by a preliminary reduction with Na2S203,followed by the addition of a known amount of K l h O 4 , the excess of which is titrated with H2C204. Alternatively, the determination may be achieved gravimetrically by reduction to selenium using hydrazine hydrochloride (63).
FUNCTIONAL GROUPS
Kaiser (52) has suggested that results of quantitative organic functional group analysis be uniformly expressed by a functional number, F , which gives the weight per cent of the "functional element" in the functional group under consideration.
F
=
meq g
meq X 0.1 x n X at. wt. of functional elements g
- milliequivalent of functional group per gram of sample
Acid Anhydrides. Anhydrides have been determined by titration of the acids produced on hydrolysis with sodium hydroxide (134) (thymol blue or phenolphthalein indicator). A4mberlite IR-120 (H+form) is used to separate the carboxylic acids from the alkaline hydrolysis mixture. Acid Halides. The quantitative conversion of aliphatic and aromatic acid chlorides to NaCl and acyl iodides by reaction with N a I in dry acetone is the basis of their analysis (121). After the XaC1 is separated, dissolved in water, and the unreacted NaI removed with FeNH4(S04)2,the chloride is analyzed by the Volhard method. Acids. illiphatic acids can be determined with a relative standard deviation of 0.48 by conversion to the corresponding 2-alkylbenzimidazole through reaction with o-phenylenediamine (129). The benzimidazole is titrated with HClO4 in acetic acid using a 9-(diethylamino)-5H-benzo[alphenoxaz5-one indicator. Acidic or neutral aqueous solutions of Xe03 oxidize carboxylic acids quantitatively, the excess Xe03being determined iodometrically (48). The procedure requires long oxidation times (2 hr a t 40' C) for monocarboxylic acids. Amines, alcohols, aldehydes, and ketones interfere. Titrations cf high molecular weight fatty acids may be carried out using a sodium methoxide in benzene titrant and a 2-propanol-pyridine solvent (126). Methanol is recommended as the solvent in the titration of mono- and dibasic acids with lithium methoxide (91) as lithium methoxide appears to be less affected by C 0 2in this solvent. iin apparatus for titrations of acids in liquid ammonia with KNH2 has been described by Schenk (117). Specific carboxylic acids containing easily oxidizable functional groups are frequently determined by redox methods. Mercaptosuccinic acid may be determined by titration with Fe(C104)3to a blue end point (97) and thioglycolic acid may be determined by titration with chloramine-?' to a starch-KI end point (73). It has been found in a study of the effect of pH on the oxidation of tartaric and glycolic acids by permanganate that reaction is quantitative a t pH 4.0 and 4.5 (IO). The oxidation requires 0.5 to 1hr at 40" C. Alcohols. A critical review (62 references) of recent acylation procedures for the determination of organic hydroxyl compounds has been published (77). VOL 40, NO. 5, APRIL 1968
413 R
The succinic anhydride-pyridine acylation method previously used for the determination of primary and secondary amines (89) has been extended to the analysis of alcohols (90). Phenols interfere but water. aldehydes, ketones, and ethers do not. 1,2-Dichloroethane is reported (72) to be preferred over ethyl acetate as a solvent in the Fritz-Schenk (34) perchloric acid catalyzed acylation procedure. o-Sulfobenzoic anhydride has been employed as acylating agent in the determination of hydroxyl compounds ( 4 7 ) . The reagent seems to offer no particular advantage over acylating agents previously employed. The perchloric acid catalyzed acetylation method has been adapted to the determination of sterically hindered cyclohexanols and secondary alcohols (150). The temperature rise resulting from the reaction of a carboxylic anhydride with alcohols can be used to determine the number of hydroxy groups present in the sample (103). Secondary alcohols can be analyzed by a dehydration procedure using a cumene solvent (80) in the presence of SOz. The water thus obtained is titrated with Karl Fischer reagent. A simple and rapid procedure for the determination of hydroxy groups in polyether pol~70ls(32) involves reaction of the compound with LiBIH4 followed by measurement of the hydrogen produced. Polyethylene glycols and certain derivatives are precipitated quantitatively with Ba(BPh&. The excess Ba2+ is titrated with EDTA to a methylthymol blue end point (76). Aldehydes and Ketones. Recommended laboratory procedures for the determination of carbonyl and derived functional groups have been reviewed
(4.41.
In a study of the S a B H 4 method for the determination of the carbonyl group (132),it has been found that aldehydes, ketones, and keto esters can be analyzed in the presence of other functional groups with an error of +3%. Carbonyl groups in dialdehyde starch could be determined with a standard deviation of less than 0.770 using the SOdium borohydride method (140). The oximation method has been used t o determine cyclohexanone, vanillin, acetone, methyl ethyl ketone, acetophenone, and formaldehyde with an accuracy of *0.2% (60). The mixed indicator of Dimethyl Yellow and methylene blue was employed. Isolated ketone groups in steroids react quantitatively with hydroxylammonium salicylate at 100' C during 2 hr (40) in a CHC13-MeOH solvent. Excess reagent is back-titrated with HCI t o a Dimethyl Yellow methylene blue end point. The accuracy of the method is =t1.570. 41 4 R
ANALYTICAL CHEMISTRY
Furfural has been determined in nonaqueous solvents with an error of *5% by titration with water to the appearance of turbidity (125). Although acetone interferes with the colorimetric determination of furfural using HIO3, a titrimetric compensation procedure permits analysis t o within 3% (133). A control, prepared from equal volumes of a standard and the furfural sample solution, and the samples are treated with a KI03-H2S04 mixture. After reaction and dilution, the samples are titrated with pyrosulfite. Amides. The ion exchange resin method for the determination of acid anhydrides is also applicable to the analysis of amides (134). Most amides can be titrated directly in nonaqueous solvents using HCIO4 (143). The procedure does not distinguish between primary, secondary, or tertiary amides. Amines. Acylation procedures for the determination of amines and alcohols have been reviewed recently ( 7 7 ) . The amino groups in aromatic, aliphatic, and cyclic amines have been detected quantitatively using o-sulfobenzoic anhydride a$ acylating agent (47). Aromatic amines may be determined by bromination with excess standard bromate-bromide mixture (81). The excess brominating agent is titrated with CuCl solution. When specified concentration limits and reaction conditions are followed, aromatic amines (such as toluidines, aminophenols, aminobenzoic acids, and sulfanilic acid) are oxidized reproducibly with XaCIOz ( 2 ) . Excess oxidant is determined iodometrically. The analysis of p-phenylenediamine and its N-alkyl derivatives depends upon its oxidation to quinone by bromine (76). The quinone is determined iodometrically after removal of excess bromine by phenol, or the ammonia or amines produced are removed by distillation and titrated. The chromatographic titration procedure using cation exchange papers as indicator (68) has been extended to the determination of heterocyclic bases (69). 11ethods available for the analysis of piperazine have been reviewed (4). Sodium tetraphenylboron has been used as titrant and dichlorofluorescein as indicator in the determination of long-chain quaternary ammonium salts (79). Carbon-Methyl Groups. The Kamer permanganate, and the KuhnRoth chromate procedures, as well as other methods for the determination of carbon-methyl groups have been reviewed (128). Esters. Saponification of most esters is complete within 5 minutes a t room temperature when aqueous dimethyl sulfoxide is used as the solvent
(139). The excess base is determined acidimetrically . After the saponification of methyl methacrylate in a copper tube a t looo C for 3 hours, the cations and anions are removed by Varion KS and Varion AD exchange resins, respectively (66). The methyl alcohol remaining is titrated iodomet rically . Thiol esters have been determined by mercurimetric titration (with mercury o-hydroxybenzoate) of the thiol produced on alkaline hydrolysis (146). Dithiofluorescein is used as indicator. A known excess of water in a trichloroacetic acid-methanol solvent is used to hydrolyze ortho esters ($3). The unreacted water is estimated by a Karl Fischer titration. Ethers. Methods used for the microdetermination of alkoxy1 groups have been reviewed (36). Hydrazine Derivatives. Both alkyl- and arylhydrazines can be titrated quantitatively with Ce(S04)2 using an extractive end point with IC1 (182). A gasometric analysis of arylsulfohydrazides and their N-acyl derivatives has been devised (28). The nitrogen evolved on oxidation with K3[Fe(CN)8] in aqueous KiCO3 is collected in an azotometer and measured after transfer to an eudiometer with CO,. Isocyanates, Isothiocyanates, and Thiocyanates. Isocyanates have been estimated by refluxing with excess carboxylic acid hydrazide in benzene, followed by titration of the unreacted hydrazide with NaXO, in HCI (43). Isothiocyanates after conversion into thioureas with dimethylamine are titrated with o-hydroxymercuribenzoate in acid media (147). Thiocyanates are converted by base to thiols (147). Easily hydrolyzable compounds can be titrated RSCN
+20H-+
RS- + CNO-
+ HzO
directly with o-hydroxymercuribenzoate while less reactive compounds require heating with the reagent in alkaline media followed by a determination of the unreacted reagent. Organometallic Compounds. h direct titration procedure has been described for the estimation of organolithium compounds (SO). Standardized benzoic acid or acetophenone is added t o the organolithium compound in a dimethyl sulfoxide-monoglyme-hydrocarbon solvent using triphenylmethane as indicator. Alkyl groups bonded to aluminum react rapidly and quantitatively with iodine (25). The reaction serves as a basis for an iodometric analysis of organoaluminum compounds. Procedures for the simultaneous determination of metal ions in donor-ac-
using a diphenylamine indicator (86),or ceptor complexes of ferrocene with AlCla by oxidation with ferric chloride, the exand A1Br3 (109) and of ferrocene with cess being determined iodometrically tetraiodomercurate (108) have been reported. (84). The direct titration method had a Organophosphorus Compounds. A systematic error of +1.2% while the review containing 26 references disferric chloride method had a systematic error of - 1.1%. cusses methods for the selective determination of phosphorus-containing N-Bromosuccinimide has been used as functional groups (11). brominating agent in the estimation of Oxetanes. Compounds such as 3,3- the following: pyrogallol, phloroglubis(chloromethy1)oxacyclobutane and cinol, a-naphthol, and P-naphthol (156). The following procedure for the de2,6-dioxaspiro[3.3]heptanecan be titrated with a n absolute error of =tl% termination of hydroquinone and resusing H B r in acetic acid as titrant and orcinol in a mixture depends upon the Gentian Violet as indicator (57). observation that on reaction with iodine in slightly alkaline media, resorcinol Oxiranes. Compounds containing the oxirane group may be determined forms a triiodo derivative while hydroby the following procedure (62). quinone is oxidized to quinone (83). A 0.05- t o 0.2-gram sample dissolved I n acid media, quinone oxidizes iodide t o in CC14, acetone, benzene, or chloroiodine. benzene is treated with a 20% acetic acid The sample is treated with 5% NaOAc solution of tetraethylammonium broand 0.1N iodine. After three minutes, mide. The mixture is titrated with the mixture is titrated with 0.1N HClO4 in acetic acid to a Crystal Violet Xa2S203. Hydrochloric acid (1: 1) is end point. added, and the liberated iodine is Peroxides. Both dialkyl and diacyl titrated with Na&03. peroxides may be determined by reacSulfides arid Disulfides. Methods tion with aniline (98). The water thus used for the analysis of sulfides and produced from the dialkyl peroxide reacdisulfides have been reviewed (55). tion is titrated with Karl Fischer reButyllithium reacts with disulfides t o agent, while the unreacted aniline from form a thiol and thioether (158). Inthe diacyl peroxide reaction is deterteraction be tween the thioether and the mined by an indirect titration using butyllithium are minimized by using acetic anhydride. Hydroperoxides do short reaction times and low reaction not react. temperatures. The thiol is estimated Directions are given for the iodometmercurimetrically . ric analysis of di-tert-butyl peroxide Sulfoxides. Acetyl chloride reacts with sulfoxides t o form acyloxysul(1). The standard deviation of seven determinations was 0.03. fonium salts which in turn react with An indirect titration procedure is iodide to release a n equivalent of recommended as the best volumetric iodine (5). The iodine is titrated with procedure for the analysis of peracetic thiosulfate. acid solutions (26). The peracid is A method reported for the determinatreated with an excess of Ce(1V) oxidant tion of dimethylsulfoxide involves its and then the unreacted Ce(1V) deteroxidation to dimethyl sulfone with acidic mined iodometrically. dichromate (127). Phenols. It has been found in a Thioamides. The desulfurization recent study (24) that both the acidprocedure of Wronski (144) which incatalyzed and base-catalyzed acetylavolves the titration of substances such tion procedures are satisfactory for the as S-alkylthioureas with o-hydroxydetermination of monohydric and dihymercuribenzoate in the presence of base dric phenols. Trihydric phenols, aldeis not applicable to the following comhydes, ketones, quinones, enols, oxides, pounds because they do not react (14.5): pyrones, and polycyclic aromatics interN-monosubstituted thioamides containfere. The use of methylmagnesium ing an aryl group, arylthiourethanes, iodide is also quantitative for monodialkylarylthioureas, trialkylthioureas, hydric and dihydric phenol determinaand cyclic thioureas. tions. An argentometric analysis of thioThe HC104-catalyzed acetylation proacetamide has been described (104). cedure has been employed for the deThe Ag2S formed when the sample is termination of sterically hindered derivtreated with ammoniacal AgN03 is atives of phenol (150). removed by centrifugation and the Satisfactory results are obtained if unreacted Agf is titrated by the Volhard precautions are taken t o prevent the loss method. The error is less than 1-2%. of bromine in the bromate-bromide Thiols. Analytical methods for the method of determining phenols (81). determination of thiols have been reAn excess of brominating agent is used viewed (53). The use of p-chloromerand the remaining brominating agent is curibenzoic acid as titrant in the deterdetermined by backtitration with CuCl. mination of thiols has been reported Hydroquinone may be determined by (148). Thiofluorescein is used as ina direct titration a t 40-60" C in acid dicator. solution with potassium dichromate, An extraction procedure for the sep-
aration of thiols from gasoline has been described (94). The thiol is then determined by a complexometric titration. Unsaturation. T h e hydrogenation procedure in which the catalyst is generated from sodium borohydride and platinum salts and in which the hydrogen is also generated from sodium borohydride (17) has been applied to the analysis of 14 olefins with an accuracy of +1.0-1.5y0 (16). The determination of 4 representative vegetable oils was accomplished with a precision of f1.5%. Unsaturated compounds can be determined titrimetrically by generating bromine in situ from bromide and lead tetraacetate (120). The lead tetraacetate is added t o a mixture of the unsaturated compound and excess potassium bromide. The end point is determined potentiometrically. A new rapid titrimetric procedure for the determination of the halogen ratio of Wijs solution and iodine chloride has been reported (42). Total halogen is determined by Na2S2O3titration and free iodine is determined by KIOI titration in strong HC1 solution. The following procedure has been used t o determine the bromine number of natural rubber (100). The rubber sample (0.02 gram) in 10 ml of toluene is mixed with 10 ml of 20% H2S04and the resultant mixture treated with 0.1N bromate-bromide solution until the solution remains yellowbrown after five minutes' shaking. The mixture is titrated with 0.1N Ka2S20s. Thioglycolic acid can be used to determine acrylonitrile in aqueous or benzene solutions (57). MISCELLANEOUS METHODS
Mixtures. An intricate b u t satisfactory procedure for analysis of mixtures of methylamines and ammonia uses the Kjeldahl technique for total nitrogen and the Van Slyke method for primary amine plus ammonia. Ammonia was precipitated by sodium hexanitratocobaltate, then distilled from 40% sodium hydroxide and titrated with standard acid. Dimethylamine was converted to the insoluble nickel dimethylthiocarbamate and the nickel content was determined by titration with EDTA. Trimethylamine was determined by the Kjeldahl method after destruction of methylamine, dimethylamine, and ammonia by nitrous acid (113). Phenylhydrazine can be titrated with 0.2N KBr03 without interference from aniline (67). Starch and iodine are added as the indicator. At the end point, iodine is converted to II3r and fails to give a starch test. Solutions of methanol in propanol, and ethanol in propanol have been analyzed by phase titration with water VOL. 40, NO. 5, APRIL 1968
415 R
after addition of cyclohexane (111). The same method is not satisfactory for solutions of methanol in ethanol. Phase titrations of nitromethane are improved by the addition of nitrobenzene (110). Kysel (64) has suggested a graphical analysis of binary mixtures, such as polypropylene with polystyrene, which is baced on a determination of the thermal degradation product9. The validity of the method depends on the linear dependence of the degradation products on the composition of the sample. A kinetic method of analysis of binary mixtures of ethanediol, 1,2-propanediol, and 2,3-butanediol is based on the reaction of these compounds with lead tetraacetate in acetic acid ( 7 ) . The method is useful for the propanediol-butanediol and ethanediol-butanediol mixtures but is of only limited application for ethanediol-propanediol mixtures. An analysis of mixtures of phenol, 0-cresol, and p-cresol in aqueous solution is based on the rate of bromination by bromide-bromate solution and requires a calibration curve (18). ni-Cresol may be determined in the presence of p-cresol by thiocyanation because the meta isomer undergoes thiocyanation more rapidly than the para isomer. Both isomers are brominated a t approximateiy the same rate, so the p-cresol can be determined from the difference between results of the bromination and thiocyanation procedures (161). A gravimetric procedure for the analysis of mixtures of isomeric aminobenzoic acids is based on the fact that bromination of the ortho and para isomers gives 2,4,6-tribronioaniline, insoluble in base, xhile the meta isomer gives the base-soluble 2,4,6-tribromo-3amino-benzoic acid, and on the insolubility of the zinc chelate formed by the ortho isomer (12). h process described as fractional entrainment sublimation (8, 9, 107) appears t o offer promise as a technique for the separation of mixtures and should find future analytical applications. Water. The Karl Fischer method continues to be widely used and modified. A recent review is by Tranchant (135). Nolecular sieves have been recommended for the preparation of methanol suitable for the Karl Fischer reagent from technical methanol (33). The Karl Fischer method has been found suitable for determination of water in molasses ( S I ) , giving results comparable t o those obtained with the vacuum-drying method (95). Water in gaseous hydrocarbons is determined by titration with the Fischer reagent after extraction of water from the hydrocarbons with methanol in an enclosed apparatus. Water in the methanol is determined before and after the extraction (54). 416 R
0
ANALYTICAL CHEMISTRY
Hexamethylcyclotrisiloxane is reactive toward the 1: 1 methanol: pyridine solution of the Karl Fischer reagent, but the interference caused by this compound and other siloxanes can be significantly reduced by using higher alcohols in the reagent (123). Various modifications of the Karl Fischer apparatus have been described (101,106). Small amounts of water (ca. 0.2%) in tetrahydrofuran have been determined by the reaction of sodium hydride with water to give sodium hydroxide and hydrogen (35). Unclassified. The concentration of furfural in dilute aqueous sclutions (less than 2%) has been determined by phase titration with water after addition of isobutyl alcohol as a turbidity indicator (38). A determination of cyclohexanol or cyclohexanone in aqueous solutions is based on the formation of insoluble compounds having the empirical formula (C6HuO)5.2HgL.4 K I * 12 H 2 0 or ( C ~ H I O OHg12*4 ) ~ . ~ KI.13 HzO. These compounds precipitate when an alkaline solution of potassium mercuric iodide is added to an aqueous solution of cyclohexanol or cyclohexanone. At concentrations below 50 mg/liter, a nephelometric procedure is used; a t higher concentrations, the precipitates are weighed. Cyclohexanol can be detected at 5 mg/liter and cyclohexanone at 8 mg./liter (142). Formates in aqueous solution can be determined by oxidation with iV-bromosuccinimide followed by addition of potassium iodide and titration of liberated iodine with standard thiosulfate. N-Bromosuccinimide is converted by formate to bromide, carbon dioxide, and succinimide (45). A procedure for determining molecular weights of aldehydes and ketones utilizes an N-bromosuccinimide titration of the semicarbazide formed when the semicarbazone of the unknown is hydrolyzed with dilute sulfuric acid for 30 minutes (105). In those cases where the aldehyde or ketone reacts with N bromosuccinimide, it is necessary to extract the hydrolyzate with ether before the titration. .ky1 isocyanates, such as o-nitrophenyl isocyanate and 3,3’-dimethyldiphenyl-4,4‘-diisocyanate, have been determined by reaction with a known excess of 0.2147 diethylamine in chlorobenzene followed by acidimetric determination of excess diethylamine (114, 115).
Styrene chlorohydrin is reported to be converted to the corresponding oxirane by an excess of 0.5N sodium hydroxide. Titration of the excess base provides an indirect measure of the amount of chlorohydrin present in the sample (112).
A study of the use of ammonium
hexanitratocerate(1V) in acetic acid as a titrant for a-keto acids and a-hydroxy acids shows that the method is suitable for a-keto acids and for a-phenyl-ahydroxy acids (39). Primary and secondary alcohols are oxidized to carbon dioxide by xenon trioxide. This reaction has been used as the basis of a method for alcohols. The method is applicable to aqueous solutions of alcohols. A known excess of xenon trioxide is used for the oxidation and the excess is determined iodometrically (49). Amines, aldehydes, ketones, and carboxylic acids interfere. Potassium alkylxanthates (ROCS2K) and xanthic esters (ROCS2R’) react readily with dimethylamine to give xanthamides and liberate sulfide or thiolate ion which can then be titrated with a standard solution of o-hydroxymercuribenzoate (137). The reactions are : ROCSS-
+ 2(CH3)2 NH
-P
S
//
+ Sz-+ (CHa)zNHz+ ROCSSR’ + 2(CH3)2NH
ROC-N(CH&
+
S
//
+
+
ROC-N(CH3)z RS(CH,)ZNH,+ 5’-4- 2-02CCeH4HgOH + (-0zCCsH&)2S 20HRS -
+ -02CC6H4HgOH
+
+
-0zCC6H4HgSR’
+ OH-
N-Chloroaryl sulfimides [ (ArS02)2NCl] are easily hydrolyzed under alkaline conditions to give sodium hypochlorite which can then be determined iodometrically (29). Most boron-carbon bonds can be determined by oxidation with trimethylamine oxide in boiling toluene, followed by acidimetric titration of the trimethylamine formed. The method measures the boron-carbon bonds of trialkyl- and triarylboranes and of heterocyclic boron compounds, but does not measure the bonds between boron and 1-alkynyl groups (b5). Several types of silacyclobutanes can be determined by reaction with bromine or iodine. The Si-C bond of the ring is cleaved and the halogen content of the resulting silicon halides is then measured. Because silacyclobutanes are not cleaved by thiocyanogen, this latter reagent can be used for determining unsaturation in these compounds (102). Subjects of recent reviews are titrimetric methods for the determination of some commoner organic compounds (6), investigation of organic matter in natural waters (118), determination of isonicotinic acid hydrazide (149), analysis of phenothiazine derivatives ( I S ) , titration with standard solutions of
aromatic diazo compounds (78), and analytical evaluation of organotin compounds (21).
LITERATURE CITED
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Piperazin, Akad. Xauk Latv. SSR, Znst. Org. Sin., 1965, 85-114. ( 5 ) Ando, T., Bunseki Kagaku, 15, 775-9
(1966). (6) Belcher, R., Lab. Pract., 14, 10424 (1965). ( 7 ) Benson, D., Fletcher, N., Talania, 13, 1207-9 (1966). (8) Berg, E. W., Hartlage, F. R., Jr., Anal. Chzm. Acta, 33, 173-81 (1965). (9) Zbid., 34, 46 (1966). (10) Berka. A.. Hileard. S..Nikrochim. Acta. 1966. 184-73: ’ (11) Bernhait, D.- N., Treatise Anal. Chem., 13, (Pt. 2), 301-35 (1966). (12) Biehl, E. R., Li, H. hl., ANAL. CHEM.,38, 1422-3 (1966). (13) Blazek, J., Pharmazie, 22, 12946 (1967). (14) Bon, 11. D., Lukash, I. K., Pyartli, V. ill.,Zavodsk. Lab., 32,411-12 (1966). (15) Brenner, J. XIAgronomy, 9, 1149-78 (1965). (16) Brown, C. A., Sethi, S. C., Brown, H. C., ANAL. CHCM.,39, 823-6 (1967). (17) Brown, H. C., Sivasankaran, K., Brown, C. A., J . Org. Chem., 28, 214-15 (1963). (18) Burgess, A. E., Latham, J. L., Analyst, 91, 343-6 (1966). (19) Burns, ill. S., RIacara, R., Swaine, D. J., Fuel, 43, 349-54 (1964). (20) Buss, H., Kohlschuetter, H. W., Preiss, X,Z . Anal. Chem., 214, 106-9 (1965). (21) Chromy, V., Groagova, A Pospichal, O., Jurak, K., Chem. d s t y , 60, 1599-611(1966). (22) Chromy, V., Vrestal, J., Zbid., pp. 1637-42. (23)Clancy, D. J., Kramm, D. E., Talanta, 13, 531-3 (1966). (24) Clarna, A,, Lippmaa, H., Tr. Tallinsk. Politekhn. Znst., Ser. 8.215. 10919 (1964). (25) Crompton, T. R., Analyst, 91,374-82 (1966). (26) Dixon, W. T., Talanta, 13,1199-1200 (1966). (27) Donner, R., 2. Chem., 5, 466 (1965). (28) Dykhanov, N. N., Dzhidzhelava, A. B., Zh. Analit. Khim., 21, 1277-9 (1966). (29) Dykhanov, N. N., Roshchenko, A.,I., Kononenko, G. G., Metody Anal. Khzm. Reaktivov Prep., MOSCOW, 12, 79-81 (1966). (30) Eppley, R. L., Dixon, J. A,, J. Organometal. Chem., 8, 176-8 (1967). (31) Epps, E. A., Jr., J. Assoc. Ofic. Anal. Chemists, 49, 5 5 1 4 (1966). (32) Falgoux, D., Demeure, &I., Engel, J., Granger, C., Bull. SOC.Chim. France, 1967, 2516-20. (33) Frehden, O., Petroianu, S., Rev. Chim. (Bucharest),16, 587-90 (1965). (34) Fritz, J. S., Schenk, G. H., ~ N A L . CHEM.,31, 1808-12 (1959). (35) Fukala, E., Kopecny, F., Chem. Prumysl, 16, 20-22 (1966). (36) Fukuda, Y., Bunseki Kagaku, 15, 754-61 (1966). (37) Gadaskina, N. D., Tarasova, K. D., I
Monomer
dlya
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Titrations in Nonaqueous Solvents Gerald A. Harlow and Donald H. Morman, Shell Development Co., Emeryville, Calif.
T
PERIOD covered by this review (October 1965 through October 1967) has been a time of considerable activity and advance in the study and exploitation of nonaqueous titrations. Most impressive has been the development of quantitative expressions which satisfactorily describe many of the complex equilibria involved in the more inert solvents. Intensive study has led to a much better understanding of acid-base chemistry in acetonitrile and other solvents of the aprotic dipolar class. The outstanding work of I. M. Kolthoff and his collaborators deserves special mention. HE TWO-YEAR
THEORETICAL
Acid-Base Equilibria and InterIn pretation of Titration Curves. protolytic solvents most monobasic acids or bases give little or no indication of intermolecular hydrogen bonding a t conventional titration concentrations. If the dielectric constant is high, dissociation of many salts is extensive and potentiometric and conductometric curves can often be interpreted in much the same manner as with aqueous titrations. The primary equilibrium involved for a weak acid (HA) is: H.4 F? H + AKreshkov et al. (133) have studied the titration of a number of phosphoruscontaining acids in a series of alcohols and compared the calculated pK’s with
+
418 R
ANALYTICAL CHEMISTRY
the pK’s of a reference acid (HCl). The solvents tested included methanol, ethyl alcohol, I-propanol, 1-butanol, and 2-propanol. The results were interpreted without need for acid-base equilibria other than those involved in water. The influence of increasing chain length of the n-alcohols on titration characteristics was primarily on the extent of the above equilibrium. As the molecular weight of the alcohol increases the dielectric constant and the basicity decreases, thus making the acids appear weaker and reducing the “leveling effect.” Consequently l-butanol had the highest differentiating power of these alcohols. The branched alcohol, isopropyl, departed from the consistent pattern shown by the straight-chain alcohols. I t is interesting to consider acid-base equilibria in tert-butyl alcohol (D = 10.9) as compared with n-butyl alcohol (D = 17.1). The use of this highly branched alcohol as a medium for titrations has been recently reviewed by Marple and Scheppers (160). These authors point out that although most aliphatic and aromatic carboxylic acids gave no indication of intermolecular hydrogen bonding, it does occur in exceptional cases such as with p-hydroxybenzoic acid. This acid precipitated during the titration in the form of a trimer (salt). Intramolecular hydrogen bonding is used by these authors to explain conductometric titration curves of dibasic acids where conductance
increases linearly to the first equivalence point, decreases between the first and second, and rises sharply beyond the second equivalence point upon addition of excess titrant. The chelated anion structure distributes the negative charge, with the result that it tends to associate very little with the large cation. Beyond the first equivalence point the cyclic structure is destroyed and the doubly charged anion associates much more strongly. By means of KMR studies Silver et al. (206)have shown that chelate homoconjugation in the mono-anions of polycarboxylic acids occurs even in methanol and water mixtures. Titration curves were obtained by plotting chemical shifts against equivalents neutralized. Puzzling results were obtained for the tetrafunctional pyromellitic acid, Solvent deuterium isotope effects on similarly hydrogen-bonded dicarboxylic acid mono-anions were studied by Eyring and Haslam (63). Also using NMR data Cocivera (42, 43) studied proton exchange involving ion pairs of ammonium salts in tert-butyl alcohol and concluded that the anion was bonded to only one N-H proton. I n the aprotic dipolar solvents the interpretation of titration curves involves additional equilibria. Hydrogenbonded acid-ion complexation may become so strong that inflections are obtained a t the half-neutralization point for a monofunctional acid or base. This tendency of an acid (HA or BH+) to
