Potentiometric Titrations Royce W. Murray and Charles N. Reilley, Department of Chemistry, University of North Carolina, Chapel Hill, N . C.
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paper summarizes the chief trends in the development and applications of potentiometric methods of analysis since the last review in this series (1529, covering the period from January 1962 to December 1963. Bates and Guggenheim (17) have reviewed the degree of standardization of p H terminology and standard buffers in Great Britain, United States, and Japan. Van Rysselberghe (255) has examined possible definitions of p H a t low and a t high ionic strengths and compared these with some aspects of the report on the standardization of p H by Bates and Guggenheim (17). Many practical aspects of p H measurement have been described by Mattock (142). A review of the applications of the mercury indicator electrode in potentiometry, with emphasis on chelometric titrations, has been published by Schmid (193). Franswa (77) has reviewed the area of nonaqueous titrations. A comprehensive book on potentiowmetric titrations has been written by Cihalik (55). Certain aspects of the use of antimony electrodes for pH measurement have been reviewed by Simchen (209) and Havelka (96). Charlot and Tr6millon (52) have reviewed a number of electrochemical indicating systems. The analytical applications of alkali metal ion-responsive glass electrodes have been reviewed by Mattock (143). The use of hydroquinone as a standard reducing titrant in redox anal3 viewed by Z i k a (250). Equivalence point detection for most methods reported is potentiometric in nature. HIS
THEORETICAL DEVELOPMENTS
Photo-Induced Potentials. Surash and Hercules (220) have investigated the photo-induced changes in the potential of a Idatinurn electrode immersed in deaerated ethanolic solution of various organic compounds. The potential became more ncgative rapidly after irradiation; a slow decay resulted upon removal of the irradiation. The potential is interpreted as being due to a free radical product of a reaction of the .solvent with the excited state of the solute molecule. Standard Potentials. Evans and Lingane (74) in an interesting paper on standard potentials of gold-containing couples were able to demonstrate that the 1)otential-determining couple is the 370 R
ANALYTICAL CHEMISTRY
AuBrz-/Au couple, rather than either the AuBr4-/AuUrz- or the AuBr,-/Xu couple. This was accomplished by comparing the potential-time behavior of a gold electrode in an equilibrating solution with the concentration-time dependency of the AuBrz- and AuBrrspecies. Metal Ion-Sensitive Glass Electrodes. Garrels, Sato, Thompson, and Truesdell (81) have prepared glass electrodes suitable for measurements of divalent cation concentrations. The five glasses studied have compositions in the classes of natural silicates such as obsidians or tektites. Empirical and theoretical equations are presented to describe the selectivity among divalent cations and insensit,ivity to moderate univalent cation concentrations. Most electrodes show response interpretable as displaying near ideal solid-solution behavior of the cations in the glass surface. Eisenman and Karreman (70, 72,108) have taken steps toward a more comprehensive theoretical treatment of the origin of potentials of metal ion-hensitive glass electrodes. In earlier work a theoretical treatment for relative selectivity of the glass surface toward alkali metal cations was presented (71). Relationships which depict the potential of the glass membrane as that of a nonideal ion exchange system separating two aqueous solutions have now been derived. The total membrane potential is comprised of a diffusional component and a phase boundary component. The basic innovation of the membrane potential theory is the use of an experimentally well-established empirical mass-action expression for the ion exchange process. Preliminary experimental efforts by the authors indicate that the phase boundary potential component may be dominant. Nikol’skii and Shul’ts (155-157) have published a revised ion exchange theory for glass electrodes which includes the effects of variation of bond strengths between the anion of the glass and the solution cation. Calculated curves for various assumed association strengths were compared to experimental data with reasonable success. Lengyel, Cs&kv&ri, and Eoksay (127) have derived equations describing the competitive equilibrium between protons and alkali metal cations for surface sites on a glass electrode to account for alkaline errors. iigreement is obtained between calculated and experimental
values for sodium ion errors. The influence of the glass composition has also been examined (126). A similar theoretical approach has been employed by Olfth (160). Stern (215) has investigated the behavior of a cell consisting of silver chloride-sodium chloride melts of varging composition separated by a Vycor glass membrane. It is shown that’ most of the membrane current is carried by the sodium ion. The cell behaves as a concentrat’ion cell toward sodium when only traces of sodium are present on one side and the other side is essentially pure sodium chloride. Hydrogen-Sensitive Glass Electrodes. Hammond (91) has reinvestigated the deuterium ion response of the glass electrode in deuterium oxide. A potential t u . p D plot for six acids of known dissociation constant produced a slope of 59.3 mv. per pD, confirming previous results in this solvent. The mechanism of current flow across the glass electrode membrane was also re -esamined , using electrolysis experiments across a membrane in cont,act with a solution of hydrochloric acid containing some tritium oxide. By the absence of any tritium on the other side of the membrane after electrolysis it was established that the hydrogen (or tritium) ion carried less than 2 X of the total current through the glass. This observation supports earlier experiments which were less sensitive toward proton transfer through the glass. McDougall and Long (131) have measured pK values for a number of weak acids in wat,er and in deuterium oxide using bhe glass electrode. The authors’ data, combined with the available literature values on other compounds, support the assertion that the difference between the p K values in the two solvents increases with pK. The rate of increase is apparently different for different compound types. Marked deviations from this behavior are discussed in terms of hydrogen-bonding effects. Beck et al. (20) have studied the time variation of the glass electrode potential following transfer of the electrode from one solution to another. The types of time-dependent behaviors could be classified into (A) a rapid change over about 1 minute to a steady value, (13) a slight or zero change, or (C) a rapid change which slows down with time but does not reach a steady potential even after several hours. The elec-
trodes tested fell into two classes depending on which of the behavior types were observed under given conditions. The two classes were identified as sodium glasses recommended for use in the p H range of 1 to 9 :tnd of resistance 200 Mohms. Schwabe et al. (194) have compared the acid error of AIacInries glass electrodes in aqueous hydrohalic, sulfuric, and phosphorit: acid solutions with the absorption of these acids in the water-swollen l a j e r of the glass. The absorption uptakt: was determined by radioactive labeling of the acid anion. The acid error was roughly proportional to the uptake for the hydrohalic acids. No uptake could be me;tsured for sulfuric and phosphoric acids. Nonaqueous Solvents. T h e equilibrium processes of acids a n d their sodium salts in anhq drous ethylenediamine solvent have been studied by Eruckenstein and JIc kherjee (43) by means of hydrogen elwtrode potential measurements. Relative acid dissociation constants for several phenols were determined from datr. a t low phenol concentration. At hig;her phenol concentration, association of phenolate with phenol occurred and equilibrium constants were obtained. The electrode potential for sodium s d t solutions was independent of concentration; a new method for evaluating relative acid dissociation constants from data in such sdutions was described. A thorough study of the acid-base properties of dimethj~lformamide has been conducted by ’I‘eze and Schaal (231). The autoprotolysis constant for this solvent was determined as lo-’* from potentiometric measurements. h variety of acidic substances could be titrated using lithium isoprolioside in ethanol as titrant. Hydrochloric acid was demonstrated t o be a strong electrolyte in this solvent. The K , and Ka values for dimethylforrnamide in water were measured by cryoscopic techniques. SIarple and Fritz (I 37) investigated the acid-base equilibria in tert-butyl alcohol by potentiometric, spectrophotometric, and conductometric techniques. ciation constants for ic, and benzoic acids, 2,4dinitrophenol, and several tetrabutylammonium salts were evaluated. A glass elwtrode acidity ,scale was established. Nine common solvents have been esamined by Crabb and Critchfield (62) for diff ercn t iat ing titrations of mistures of phenols. Two methods of defining differentiating capability of a solvent’ were discaushed. The slopes of the linear plots of half-neutralization potentials (values refwred to that ’or benzoic acid) againqt aqueous pK,, values reflect
solvent differentiating qualit’y in a quantitative manner. h practical and more easily obtained qualitative measure of differentiating ability could be obtained from the magnitude of the first potential break in a titration of a misture of phenols. The two methods xere shown to agree very well. The study concluded that tert-butyl alcohol was superior t o the other solvents examined. Bates, Paabo, and Robinson (18) have examined the problem of p H measurements in alcohol-ryater solvents. From measured values of liquid-junction potential plus log (,Yc,)(where r n is ~ the~ primary medium effect’ for the chloride ion of the reference electrode), it was established that liquid-junction POtentials are functions only of the compobition of the medium and are essentially independent of the composition of the buffer solution over a wide range of pH values. h suitable scale of p H for these media can thus be described, and methods for the practical standardization of p H measurements in these media are outlined. Selson and Iwamoto (154)have investigat ed the usefulness of four reversible redos couples for experimental measurements of liquid-junction potentials. Based on comparisons of voltammetric data over a wide range of different solvents, the tris(4,7dimethyl-l, 10-phenanthro1ine)iron (11)-(111) couple was recommended. The effect of the structure of a quaternary ammonium titrant, as reflected in its ion pairing influence on titrations of weak negatively charged acids in nonaqueous media has been investigated by Harlow (93). Differences sufficient t o cause some dicarboxylic acids to titrate as monoprotic vvith one titrant and as diprotic with another were demonstrated. Cheng, Howald, and Miller (53) have studied the behavior of the glass electrode in glacial acetic acid. Reproducible potential measurements (5 mv.) could be attained under certain conditions. The platinum-chloranil-tetrachlorohydroquinone electrode vias employed as reference. The negative “acid error” present for dry solutions of hydrochloric acid was interpreted in accordance with current theories. The effects of water on the “acid error” and on the titration of hydrochloric acid with sodium acetate were examined. The water effects on the titration points could be quantitatively represented by an equation. Mcasurements showing the effect of added potassium chromate on the potential of a concentration cell of silver nitrate in molten potassium nitrate have been reported by ;\lvareaFunes and Hill ( 5 ) . The data are interpretable in terms of the quasilattice theory (40) for molten salt solu-
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tions. The association energies for assumed coordination nunibers of 4 and 6 and the 1 to 1 association constant were calculated and were found to be larger than the corresponding values for the similar system involving sulfate (240). Distribution Coefficients. Christensen (64) has reported the pertinent theoretical expressions for the potentiometric titration determination of distribution coefficients of acids or bases between water and an organic solvent. The basis of the method is the shifting of the titration curve position (from that in pure water) in the presence of the extracting organic solvent. Experimental results for several compounds were found to be in satisfactory agreement with known values. The same principle with a different experimental approach has been employed by Urandstrom (42) for the distribution coefficients of bases. Xfter partial titration of the base hydrochloride in water, using an automatic pH-stat to attain a selected p H value, a known quantity of organic phase is added and the pH-stat adds an additional quantity of titrant t o restore the p H to the selected value. Pertinent equations and a n experimental example are given, Polyacid Neutralization. Bak ( 9 ) has derived expressions relating t h e apparent p K , the degree of neutralization, and the energy of interaction within a molecule for the titration curves of polymer polyacids. The analogy of the theoretical approach used to previous work is noted. Experimental data for a polyacrylic acid are discussed. Mitra and Chatterjee (149) have described the p H and conductometric titration curves for four polynuclear phenolic compounds containing two, three, four, and five phenolic groups. Six solvents varying in basic character and dielectric constant were employed; titrants were’sodium methoxide or tetramethylammonium hydroxide. The effects of hydrogen bonding, solvent, and ion association on the titration curves are discussed in detail. Hydrogen Electrode Polarization. Cosijn (60) has studied the diffusion polarization of a hydrogen electrode (platinized platinum). The results are in excellent agreement with the proposed theory (61) except in unbuffered alkaline solution. The conclusion is reached that the redox system (H2, H 2 0 , H + , OH-) behaves reversibly a t the platinized platinumhydrogen electrode and that the currentpotential curves in both buffered and unbuffered solutions are entirely controlled by diffusion a t a stationary electrode. Titration in Concentrated Salt Solutions. Investigations of acid-base equilibria in concentratcd salt solutions havc bcen rcportrd by Iiosrnthal VOL. 36, NO. 5 , APRIL 1964
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and Dwyer (69, 185-187). The acidbase titration features that result from the addition of large quantities of inert salt are explained by the variation of the composite activity coefficient term, QBH, and its influence on the equilibrium expression
where KBH is the thermodynamic dissociation constant and the quantities in brackets are the concentrations of the species in question. Thus, KBi,/QBH is considered to be a constant for a given acid or base in a particular salt solution and is a “concentration equilibrium constant.” This is to be expected when small quantities of acid or base are titrated in concentrated salt solutions because the total salt content does not vary appreciably during the titration. The value of QBH is estimated from the known thermodynamic constant, K B H , and some experimental measure of the concentration of H + a t some point during the titration (where [l{]/[l5H] is also known). Either of two methods is employed to indicate the concentration of H + ; one uses e.m.f. measurements with a glass electrode and the other uses a suitable colorimetric indicator. In either method calibration for a given concentrated salt solution is first made by making measurements after known incremental additions of strong acid or base. Subsequently eit’her method can be employed in the same concentrated salt solution to obtain the concentration of H+. The values of QBH were found to vary from 10°.2*in 1.11 LiCl to in 9.11 LiCl for p-aminoazobenzene and o-nitroaniline, respectively. The value of &BE< is highly dependent upon the base in question. In 4-11 LiC1, the following values for log Q B H were obtained: 0.87 (aniline), 1.15 (2-aminopyrimidine), -0.02 (acetate ion), and -0.115 (formate ion). Larger end point breaks (relative to dilute aqueous conditions) are secured, of course, for those concentrated salt solutions where large values of Q B H are found. APPARATUS
Instruments. An automatic coulometric titration assembly employing potentiometric end point anticipation and detwtion has been described by Scott and Strivens (195). The batterysupplied generator current is controlled by ihdicating electrodes through a commercial titrator controller, the current being decreased near the preset potential chararterizing the end point. An operational amplifier integration circuit is emplo>.ed to measure the total current, 372 R
ANALYTICAL CHEMISTRY
flow. Application to several common titrations is described. An automatic coulometric titrator based on similar principles and methods of end point anticipation, but) utilizing a motor revolution technique for current integration and with added features of automatic dispensation of samples, has been reported by Jeffcoat and hkhtar (106). -4coulometric titrator for continuous streams has been described by Takahashi (222, 228, 229). The sample and electrolyte solution are pumped to the cell a t a constant rate. The current applied to the generator electrodes is controlled by an electronic servosystem so as to maintain a solution composition producing a selected potential difference between the pair of appropriate indicating electrodes. The level of applied current, which is proportional to sample concentration a t all times, is recorded. The apparatus has been applied to continuous base determination using acid electrogenerated from water oxidation (223, 227), arsenic (111) determination using electrogenerated bromine (228)) residual chlorine determination in city water using electrogenerated iron(I1) (224), halide determination with electrogenerated silver ion (225), and copper (11) determination by precipitat,ion with electrogenerated ferrocyanide (226). A constant current coulometric titration for bromine numbers (olefinic unsaturation) has been described by Baumann and Gilbert (19). Dual polarized platinum electrodes provide the potentiometric end point detection; the behavior of the indicator electrodes is discussed in detail. The method is recommended for low bromine numbers. Stock (216) has devised a Pimple automatic titrator capable of potentiometric end point anticipation. Anton and Mullen ( 7 ) have devised a multipurpose automatic recording titrator unit based on a modified Precision Dow recording titrator. The assemblage has capability of volumetric or coulometric titrant addition and potentiometric, amperometric, thermometric, conductometric, or photometric (adsorption, scattering, or fluorescent modes) equivalence point detection. An automatic potentiometric or amperometric end point detector for coulometric titrations has been designed by Roberts and Ibejcha (183). No end point anticipation is provided. A pHstat, suitable for maintaining pH constant within +0.01 pH unit for at least one day, has been described by Josefsson, Ryberg, and Svensson (107). Leake and Reynolds (125) have designed a servo-type titration apparatus for use in titrations in which the attainment of steady potentials after additions of titrant is slow. Friedman and IZoivers (78) have desrribed an analog computer approach
for the cation nonspecificity correction for potassium ion glass electrodes used for continuous potassium ion measurements. The computer described is programmed for the Eisenman equation and the sodium ion correction term is experimentally monitored by a sodium ion electrode. Esperimental results described show a satisfactory performance of the apparatus. .in automatic apparatus for the determination of pK, and molecular weight of microsamples of organic acids has been described by Wilson and hlunk (643). Kordatzki (121) has constructed a dual-purpose instrument for the measurement of pH and conductance. Petersen (168) has discwsed errors arising in pH measurements at different temperatures using commercial pH meters. Wise and Guerry (247) have described a simple capillary flon-controlled buret suitable for recording potentiometric titration curves. A short section of capillary glass tubing, inserted through a rubber stopper placed at the top of a conventional buret, controls the rate at which titrant can flow by restricting the rate of air flow to the inside of the buret. Stock and Fill (217) have designed two electronically operated titrant valves for use in automatic titrators. Electrodes. Kikulin and Tsypin (168) have obtained data on the dependency of the potential of a silver >ingle crystal electrode on the crystallographic direction. The differences between the various crystal faces are functions of the solution electrolyte, demonstrating the importance of the electrolyte-metal interaction in determining electrode behavior. Izidinov, Borihova, and Veselovskii (100) have investigated the electrochemical and photoelectrochemical behavior of monocrystalline Filicon electrodes. The potential-time and potential-photon behavior in basic solutions was established and discussed in terms of surface react ions. Csing a specially designed apparatus, Plumb (173) has measured the potentials of aluminum electrodes having varied degrees of surface osidation. By extrapolation to zero osidation, the potential of an oside-free surface and the free energy of formation of aluminum ions could be obtained. Samodelov (188) has prepared a cationic ion exchange membrane saturated n.ith scandium ion which responds reversibly and in a Nernstian fashion to that ion over a concentration range of 0.05 to 1.OJI. Spencer and Lindstrom (214) have used an ion eschange membrane electrode to detect elution of sodium and potassium ion from an ion eschange chromatographic cohimn. The eluent supply and column eluent
flowed past opposite sides of the membrane; a difference in their composition a t the elution point produced a potential peak. Materova and Yurchenko (139) have esamined the usefulness of membranes prepared from the ion exchange resins AV-16, AV-17, and EDE-10 (Russian) as indicator electrodes in acid-base and precipitation titrations. End points for neutralization titrations were not spectacular, whereas reasonable breaks were obtained for halide and sulfate precipitations. Bishop and Dhanesh war (31-33) have conducted a n espericiental survey of silver- and halide-responsive electrodes. Silver metal, silver halide, gold and silver amalgam, and cation-selective glass electrodes were examined and compared with respect t o preparation, aging effects, and respmse t o silver ion and halide ion down t o limiting IonT concentrations in aqueous and partially aqueous media. Labrie and Lamb (162) have constructed an electrode s,ystem t o indicate sodium ion in melts The electrode consists of a porcelain tube, which behaves as a reversible membrane electrode, enclosing a sodiu m-silver chloride melt and a silver wire electrode. Portnoy, Thomas, and Gurdjian (17'4) have described an improved method for construction of sodium- and potassiumselective glass electrodes for use in continuous measurements. The electrodes are capable of detecting a change of 5 X 10-4X sodium or potassium in the biological ranges of 2 to 6 X 10-3X potassium and 0.13 to 0.15111 sodium. When used for continuous measurements a simple circuit was employed t o reduce the sodium error of the potassium electrode to less than 2.5 X 10-4M for changes of I;odium from 0.13 to 0.15.11. The properties of two commercially available sodium ion-responsive glasses for electrodes have been assessed over a wide range of conditions by Mattock (144). Selectivity, useful concentration ranges, and temperature effects are reported. The 13H68 glass is recommended for general-purpose laboratory use, the I3H104 glass for more accurate work with strong sodium solutions. Budd (46) has studied the response of two commercially available glass electrodes (I5eckman 39278 and 39137) towards silver ion concentration. One of these was found to be more sensitive to silver than to hydrogen ions and t o be highly selective for silver over other cations. A response of 56 mv. per tenfold change in silver ion concentration was observed at 25" C. A patent by Eisenman, Rudin, and Casby (73) describes a potassium glass electrode of high selectivity. The electrode consists of an alkali oside and aluminum oside (in a mole ratio 1 t o 5 ) misture in a network-forming oside
matrix. The degree of response of a potassium glass electrode toward other alkali metals has been studied by Materova, hfoiseev, and Belyustin (139). Radiotracer and potential measurements showed a n increasing response in the order cesium, lithium, rubidium, and sodium. Petrovski and &ta (169) have empirically established an optimum barium-sodium glass composition for minimizing sodium error in pHsensitive glass electrodes. Shul'ts et al. (203) have esamined various techniques for characterization of different glasses. Potential-pH curves and soaking esperiments in various media (for chemical stability) were recommended. These types of experiments and the revised glass electrode theory were applied t o the study of a wide variety of glass types: lithium silicate (206) and sodium silicate (204) glasses with added beryllium, magnesium, calcium, and barium oxides, lithium silicate glasses with added aluminum, gallium, and boron osides (607), added rare earth osides ( I & ) , added zirconium oside (202), added barium and lanthanum oside mistures (206), added cesium and lanthanum oxide mistures (201), added cesium and barium oxide mistures with traces of other metal osides (164), sodium silicate glasses with added Group IV and V metal clsides (23).and nonsilicate glasses (41). Shul'ts (200) has summarized the above and other related papers. A glass electrode for acidity determinations in acetonitrile, designed by Badoz-Lambling, Desbarres, and Tacussel (8),consists of Corning 015 glass, an inner metal foil shield, a filling solution of lithium and silver perchlorate, picric arid, and diphenylguanidine in acetonitrile, and a silver wire. Some esperimental titration data are given. Halsey and Burkin (90) have noted the adsorption of n-dodecylamine on glass electrode surfaces under certain solution conditions. The adsorption resulted in improper functioning of the electrode and rendered p H measurements invalid. 13ishop and Short (38) have investigated the applicability of dual polarized antimony electrodes for potentiometric acid-base titrations. Response curves give accuracy comparing favorably with conventional methods. Temperature effects have also been esamined (39). The utility of pyrolytic graphite as an indicating electrode in acid-base and redos titrations has been esplored by Niller (148). d microelectrode assembly for measurement of p H within 0.1 mm. from a corroding metal surface has been devked by Mori, Loesg. and Draley (151). The utility of the silversilver citrate electrode to the determination of stability constants of metal citrate complexes has been investigated by Ptitsyn, Vinogradova, and Vasil'eva
(177). Linearity of the espected potential-citrate concentration relation was obtained only in the narrow range 3 x to 10-3Jf citrate, severely limiting the range of application of this elecJanz and Saegusa (103) have esamined the osygen electrode a t platinum and gold in molten carbonate medium at 600" to 800' C. by the criteria for reference electrodes. The potentials were found to be stable and reproducible and to eshibit a satisfactory degree of reversibility. A procedure for preparation of mercury-coated platinum electrodes has been described by Ramaley, Hrubaker, and Enke (178). .I stainless steel indicator electrode has been found by Smith, I3iswas, and Vosburgh (211) t o be suitable for the titration of hydrogen peroiide with permanganate. The polarizability of the saturated cealomel electrode has been esperimentally investigated (199). Liu (128) has determined the standard potentials of the copper (0)-(I) copper (I)411) palladium (0)-(II), and rhodium(0)-(111) couples in molten lithium sulfate-potassium sulfate eutectic. The silver(0)-(I) couple was used as reference. All couples studied exhibited Sernstian behavior. ~
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APPLICATIONS
Analysis Based on Measured Potentials. Friedman and Sakashima (79) have compared the sodium glass electrode and flame q)ectrophotomet,ric techniques for determination of sodium ion in natural and biological media. The glass electrode technique produced somewhat higher precision in the analysis. In measurements of sodium in plasma, glass electrode result3 were lower than the flame data by an amount proportional to the sodium concentration, suggesting a specific sodium binding effect in the plasma medium which affected the glass electrode technique to a greater extent than the flame method. h null-point potentiometric method for the microdetermination (10 p.11.m.) of fluoride has been described by O'Donnell and Stewart (159). The method is based on the redos potential of a cerium(IV/III) coul)le in the presence of fluoride. A sodium-sensitive glass electrode was employed by Hyman (99) for direct potentiometric wtimation of the apparent sodium ion activity. l'he effects of hydrogen and potassium ions and of added dextrose were investigated. 'I'shernyak (233) has reported a method for determination of sodium in aluminum alloys based on the use of a sodium-sensitive glass electrode. l'he sodium is separated by
VOL. 36, N O . 5, APRIL 1964
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The applicability of the sodiuniresponsive glass RH68 for silver ion measurement in the absence of sodium ha., been investigated by Mattock and Uncles (145). The use of the glass electrode for evaluating the acidity of petroleum products dissolved in alcohol-benzene solvent has been investigated by Izmailov and -\leksandrova (101). GordievskiI, Filippov, and Kupryunim (86) have employed an ion exchange membrane electrode for acidity measurements in 0.0016 to 28.05 hydrofluoric acid solutions. The expected potential-concentration relation mas obeyed over a wide concentration range. No interfering ions were noted. I'flaum, Frohliger, and Berge (170) have employed a silver-2.1 -I ver bromide electrode for the determination of pBr. .In accuracy of *2 mv. over a concentration range of lo-' to M was obtained. Scarano (290, 191) has determined trace amounts of dissolved oxygen by potential measurements using the aluminum electrode. Analysis Based on Reaction Rates. Kramer, Cannon, and Guilbault (113) have developed a kinetic method for cholinesterase and acetylcholinesterase, based on measurement of the rate of enzymatic liydrolyiis of a thiocholine ester by the enzyme sample. Over the enzyme concentration range of 0.3 to 2 x ~ o - ~ Mthe , concentration-rate curve is linear. Rates are measured by recording of the potential difference between two platinum indicator electrodes polarized with constant current. This method ha< been extended (88) to the analysis of some highly toxic organophosphorus compounds (Sarin, Systox, parathion, malathion) which act as anticholinesterase compounds. The decrease in rateof the cholinesterasebutyrylthiocholine ester hydrolysis, as measured by dual polarized platinum indicator electrodes, is linearly related to concentrations of the organophosphorus compounds. Guilbault, Tyyon, Kramer, and Cannon (69) have determined glucose and glucose oxidase by a method based on measurement of the rate of the catalytic air oxidation of glucose in the presence of glucose oxidase. A current-polarized platinum anode is used as a rate indicator. The recorded potential changes from that of the diphenylamine sulfonic acid added a- a potential poiser to that of the hydrogen peroxide product of the catalytic reaction. Cystine a t the part per million level has been determined by Pardue and Shepherd (163) using a reaction rate mrthod. The basis of the method is the proportionality of the rate of reaction of iodine vith sodium azide to cvstine concentration. The reaction rate i s mrnsured by incorporation of thc
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ANALYTICAL CHEMISTRY
system into a concentration cell sensitive to iodine concentration. Processes in Molten Salts. Shams El Din (196) has successfully titrated dichromate in molten potassium nitrate a t 370" C. with the base potassium hydroxide. The oxygen-oxide couple a t a platinum electrode served as indicator electrode. The potentiometric titration curves gave a 700-mv. break at the equivalence point, and a theoretical analysis of the curves showed agreement uith the expected shape. I n a subsequent report (198), dichromate was similarly titrated with potassium carbonate, potassium bicarbonate, and sodium peroxide, any of which may serve as the base titrant. The presence of traces of water in the melt had little effect in these methods. I n another (197)] metaphosphate and paper metavanadate were titrated as acids, using sodium peroxide as the base titrant; chloride and nitrate melts served as the diluent. I n nitrate melt, metaphocphate exhibited two potential breaks corresponding to the formation of PzOip4and PO4+, respectively. Precipitation Processes. Kinefordner and Tin (246) have separated bromide from chloride in the biological concentration range. The separation is based on the formation of volatile cyanogen bromide, which is absorbed in sodium hydroxide solution. This sohtion is then subjected to a null point potentiometric titration of the bromide to yield part per million results in a total time of 15 minutes. Bush, Kunzelsauer, and Merrill (49) have determined hydroxyl end groups in polymers by utilizing the reaction of such groups with phosgene. .Ifter reaction, excess reagent is removed by volatilization, the chloroformate is hydrolyzed n ith aqueous alkali, and the resulting aqueous chloride sample is subjected to a potentiometric silver titration. Analytical data on several polymers are included. h technique for measurement of chloride in the concentration range 10-6 to 2 X 10-4JL has been described by Peters and Lingane (167). The chloride sample is equilibrated with pure silver chloride; a sample is drann off and the silver concentration measured by potentiometric titration i5ith iodide. The chloride concentration is then calculated from the solubility product for silver chloride. Concentrations a t IO-GJI could be determined to within 5%; the error a t l O - ~ Nwas O.S7,. Bishop and Dhanesha a r (2Yews40, Sh 15,52 (1962). (73) Eisenman, G , Rucin, D 0 , Casby, J . U , U S Patent 3,041,252 (June 26, 1962). (74) Evans, D. H., Lingane, J . J., J . Electroanal. Chem. 6. 1 1 1963). (75) Feller, H., Vincknt, B. F., ANAL. CHEM35,598 (1963). ( 7 6 ) Frank, A. J , Ibzd , .35,830 (1963). ( 7 7 ) Franswa. C. E. M I Chem U‘eekblad 59,249 (1963). (78) Friedman, S. M., Bowers, F. K., Anal. Hiochem. 5 , 471 (1963). (79) Friedman, S. &Sakashima, I., M., Ibid., 2 , 568 (1961). (80) Fritz, J . S., Marple, L . W.,ANAL. CHEM. 34, 921 (19621. (81) Garrels, R. M , Sato, M . , Thompson, M. E., Truesdell, A . H., Science 135, 1045 (1962). (82) Gopala Rao, G., Dikshitulu, L. S. A,, Tolunta 10,295 (1963) (83) I b i d . , p. 1023. (84) Gopala Rao, G . , Sagi, S.R . , Ibid., 9, 715 (1962). ( 8 5 ) I b i d . , 10, 169 (1963). (86) Gordievskil, A. V., Filippov, E. L., Kupryunim, G. I., Zh. Analit. Khim. 18, 13 (1963). ( 8 7 ) Grekov, A. P., Mrtrakhova, M . S., Ibid., 16, 643 (1961). \
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(88) Guilbault, G. G., Kramer, D. N., Cannon, P. L., ANAL.CHEY.34, 1437 (1962). (89) Guilbault, G. G., Tyson, B. C., Iiramer, D. C., Cannon, P. L., Ibid., 35, ,582 (1963). 190) Halsey, G., Burkin, A. R., .Vatwe 193,1177(1962). (91) Hammond, P. R.. Chem. Ind. (London) 1962.311 (92) Harlow, G. A., ANAL. CHEM. 34 , 148 (1962). (93) Ibid., p. 1482. (94) Zbid., p. 1487. (95) Harlow, G. A., Wyld, G . E. A., Ibid., 34, 172 (1962). (96) Havelka, S., Chem. Listy 57, 467 (1963). (97) Heuser, S. G., ANAL.CHEM.35, 1476 (1963). (98) HeyrovskL, A., Z . Anal. Chem. 173, 301 (1960). (99) Hyman, E. s., .4NAL. CHEM.34, 365 11962). 100) Iz’idinov, S. U., Borisova, T. I., Veselovskii, Y. I., Dokl. A k a d . .Vauk S S S R 133, 392 (1960). 101) Izmailov, N . A., Aleksandrova, A. M.,Tr. Khim. Fak. Kharkov Gosud. C:niv. 60, 121 (1961). 102) Jander, G., Surawski, H., Z . Elektrochem. 65, 527 (1961). 103) Janz, G. J., Saegusa, F., Electrochem. Acfa 7, 393 (1962). (104) Jaworowski, R . J., Bratton, W.D., A N A L .CHEM.34, 111 (1962). (105) Jeffcoat, K., Akhtar, M.,Analyst 87, 45.5 (1962). (106) Jones, S. L., U. S. At. Energy Comm. KAPL-M-SLJ-7 (1961). (107) Josefsson, L., Ryherg, C. E., Svensson, R., ASAL. CHEM. 34, 173 (1962). (108) Karreman, G., Eisenman, G., Bull. Math. Biophys. 24, 413 (1962). (109) Khakimova, V. K., Agasyan, P. K., Czbeksh. Khim. Zh. 6,21 (1960). (110) Khomutov, ?;. E., Eberil, V. I., Zh. Analit. Khim. 17,763 (1962). (111) Kordatzki, W.,Chemiker Ztg. 84, 606 11960). (112) Kostromin, A. I., Flegontov, S. A,, Zavodsk. Lab. 27, 528 (1961). (113) Kranier, D . N . , Cannon, P. L., Guilhaiilt, G . G., ANAL.CHEY.34, 842 (1962) (114) Kratochvil, B., I b i d . , 35, 1313 (1963). (11.5) Kreshkov, A. P., Bykova, L. Ii,, Pevzner, I. D., Dokl. A k a d . S a u k SSSR 150,99 f 1963). (116) Kreshkov, A. P., Bykova, L. S . , Rusakova, M. S., Kaxaryan, N. A., Zauodsk. Lab. 28, 11 (1962). (117) Kreshkov, A . P., Bykova, L. K., Shemet, S . Sh., Tr. X o s k . Khim.Tekhnol. Inst. 1961,327. (118) Kreshkov, A . P., Drozdov, V. A,, Vlasova, E. G., Zavodsk. Lab. 26, 1080 (1960) (119) Kreshkov, A. P., Yarovenko, A. Ii,j Zel’manova, I. Ya., Dokl. A k a d . .Vauk SSSK 143,348 (1962). (120) Kreshkov, A . P., Yarovenko, A. S . , Zel’manova, I. Ya., Zavodsk. Lab. 29, 295 (1963). (121) Kreshkov, A. P., Yarovenko, A . N., Zel’manova, I. Ya., Zh. Analit. Khim. 17,780 (1962). (122) Labrie, R. J., Lamb, V. A , , J . Eleclrochem. Sor. 106, 895 (1959). (123) Lane, E. S., Talanta 8, 849 (1962). 1124) Leake, 1,. R., Reynolds, G. F., Ibid . 9. 413 1 19621. (125) Ibih., 1 ) 421. (126) Lengyel, B., CsBkvitri, B., -4cta Chim. Akad. Sei. Hung. 25, 369 (1960). (127) Lengyel, B , CsAkvBri, B , Boksay, Z., Ibid., 25,225 (1960).
(128) Liu, C. H., J . Phys. ChPm. 66, 164 11962’). (129) I,;rrenz, O., Parks, C. R., ASAL. Cmxi. 34,394 (1‘362). (130) Macero, 11. J., Janeiro. R. A.. Anal. Chzm .4cla 27, 585 (1962) (131) LlcI)ouyall, A O., Long, F. A., J . Phvs Chem. 66.429 f 1962) (132) liackey, J . ’ L , ‘Hilc&, hl. A., Powell, J . E , I h d , 66, 311 (1962). (133) llalik, R’. C . , lluhaffaruddin. hl..’ J . Electroanal. Chpm 6, 214 (1963) (134) Malik, W L., Salahuddin, IC., Ibid., 5 . 68 11963) (13.5) llaricle, D. L., ASAL. CHEM.35, 683 1 1963) (136) %arpie, L. R., Fritz, J . S., Ibid., 34, 796 (1962) (137) Ibzd , 35, 1223 11963). 1138) I b i d , D. 1431. (139) Rlater’ova, E. A., Moiseev. V. V., Belyustin, A. A . , Zh. Fiz. Khim. 35, 1238 (1‘361). (140) Materova, E. A . , Yurchenko, V. S., Xh. ,41221 Khim 16, : B Y (1961). (141) Mathnr, S . K , Sarang, C. K., J . Elecfroanal. Chrm. 6, 211 (1963). (142) llattock. G.. “Advances in A n...a..l v t.i.’ cal Chemistry and Instrumentatio”n,” Val. 2, \Vile?, Sew York, 1963. (143) Mattock, G., .4nal. Chem., Proc. Intern Syrnp , Birmingham University Birniingham, England, 1962. (144) Mattock, G , ilnalyst 87, 930 (1962). (145) liattock, G., Vncles, R., Ibid., 87, 977 (1962). (146) Maurice, I f . J., Anal. Chim. Acta 26, 406 (1962). (147) Metcalf, L. D , ANAL CHEM.34, 1849 119621 (148) hliller, F J , Ibid ,35,929 (1963). (149) Mitra, R P , Chatteriee, S. K., Indian J . Chem. 1,62 (1963)(150) llorales, A , , Zgka, J., Collection Czech. Chem. Commun. 27, 1029 i1962). (151) >lori, S., Loem, R . E., Draley, J. E., Corrosion 19, 165 (1963). (152) Murray, R. W.,Reilley, C. Tu’.. A N A L .CHEM.34, 313R (1962). (153) Muth, C. W., Darlak, R. S., English, W . H., Hainner, A. T., Ihid., ,
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( 1 h f S i l s n n , I. Y Iwanioto, R. T., Ihid., 35, !67 (1963) 11553 Sikol skii. B P . Sllul’ts. M. M . . Venin. Leningr. (.tiit). Ser: Fiz. - i Khim. 1963. II 73. (156) Sikol’ski’l, R . P , Shul’ts, hl. Zh. F ~ zKhim. 36, 1327 (1962). (157) Sikol’skil, B. P , Shul’ts.’ M Belyustin, A. A , Ibid.’, p. 86. (158) Sikiilin, V. N., Teypin, M . I h i d , 34,2814 (1960). (159) O’Donnell, T. A , Stewart, D. .ANAL. CNEM 34, 15.17 (1962). (160) OlfLh, C., Periodicu Polytech. 141 (1!)6O). (161) Paidowski, L., A0cznii.i Chem. 763 f10601. (162) Pajdowski, L , Jezowska-Trzebiatomska, B., Ibid., p. 775. (168) Pardue, H. L., Shepherd, S., ANAL. CHEY. 35, 21 (1963). (164) Parfenov, A. I., Shul’ts, M . hl., Kochergina, X. S . , Ivanov, V. P., Eonina, S. B., Krllmykova, L. P., Ageeva, E. D., Vesln. Leningr. L:niu. Ser. Fiz i. Khim., 1963, p. 162. (165) Parfenov, A . I., Shiil’ts, M . M . , Sekrasova, T. pi., Poloi.ova, I. P , I b i d . , p. 126. (166) Paul, R . C., 1-asisht, S. K lfalhntra, K. C , Pahil, S. S., ANAL.C H E M 34. 826 119621. ( i 6 7 j Peters, D’. G., Lingane, J. J., Anal. Chim Acla 26, 7 5 (1962). (168) Petersen, G . K., Radiometer .Yews 5 , 10 (1960). ~
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(1961). (-170) Pflaum, R. T., Frohliger, J. O., Berge, D. G., ANAL. CHEM.34, 1812 (1962). (171) Piccardi, G.. -Cellini, P., Anal. Chim dcta 29, 107 (1963). (172) Piccardi, G , Cellini, P., Ann. Chim. ( R o m e ) 52, 208 (1962). (173) Plumb, R. C., J . Phys. Chem. 66, 866 (1962). 1174) Portnoy, H. D., Thomas, L. M., Gurdjian, E. S., Talantrl 9, 119 (1962). 75) Powell, J. E., .Mackey, J. L., Znorg. Chpm. 1,418 (1962). 76) Pshenitsyn, X . K., Ginzburg, S. I., Prokof’eva, I. V., Zh. Analit. K h i m . 17,343 (1962). 77) Ptitsyn, B. V I Vinogradova, L. I., Vasil’eva, L. L., Zh. AVeorgan. Khim. 7, 1009 (1962). 178) Rarnaley, L., Brubaker, R. L., Enke, C. C., ANAL. CHEY. 35, 1088 (1963). 179) Rechnitz, G. A,, Katz, S. A., Zarnochnick. S. B.. Ihid.. D. 1322. 180) Reynolds, C. A.,’ Little,’ J:, Pattengill, M . , Zhid., 35, 973 (1963). 181) Itink, M., Riemhofer, M., Rorner, H.. Deut. Apotheker-Zta. 103, 719 (1963). 182) Riolo, C. B., Soldi, T. F., Occhipinti, C., A n n . Chim. 51, 1178 (1961). 183) Roberts, C. B., Brejcha, H. A., ASAL.CHEM.35, 1104 (1963). 184) Robinson, R. T., Sensabaugh, A. J , llarkunas, P. C , Ihid., p. 770. 185) Rosenthal, D., Dwyer, J . S., Ibzd., p. 161. 186) Itosenthal, I)., Dwyer, J. S., Can. J. Chem. 41, 80 (1963). 187) Rosenthal, I)., Dwyer, J. S.,J. Phys. Chem. 66,2687 (1962). 188) SarnodFlov, A . P , Izaest. Sibir. Otdel. Akad. .Vnuk S S S R 1961, 43. 189) Sasena, It. S., Mittal, hl. L., J. Electroanal. Chem. 5, 287 (1963) 190) Srarano, E., Ibid , 2 , 432 (1961). 191) Ihid., 3, 304 (1962). 192) Schilt, A. A,, Anal. Chzm. Acta 26, 134 (1962). 193) Schmid. R. 1%’ , Chemist-ilnalyst 51, 36 (1962) 104) Svhwabe, K.. Dahms, H., Xguyen,
380 R
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Q.,Hoffrnann, G., Z . Elektrochem. 66, 304 (1962). (195) Scott, P. G. W., Strivens, T . A., Analyst 87,356 (1962). (196) Shams El Din. A. M.. Electrochim. Acta 7,285 (1962).‘ (197) Shams El Din, A. M., El Hosary, A. A,, Gerges, A. A. A,, J . Electroanal. Chem. 6, 131 (1963). (198) Shams El Din, A. M., Gerges, A. A . A , , Ihid., 4, 309 (1962). (199) Shams El Din, A. M., Xilsson, O., WranglBn, G., Zhid., 2, 497 (1961). (200) Shul’ts, M. M., Vestn. Leningr. Univ. Ser. Fiz. i Khim., 1963. p. 174. (201) Shul’ts, hl. M., Parfenov, A. I., Ch’en, Te-Yu, Bondarenko, T. G., Mekhryushev, Yu. Ya., Ihid., p. 155. (202) Shul’ts, M. M., Parfenov, A . I., Panfilova, 5 . P., Ihid., p. 143. (203) Shul’ts, M. M.,Parfenov, A. I., Peshekhonova, N. V.,Belyustin, A. A., Ihid., p. 98. (204) Shul’ts, M. M., Peshekhonova, S . V.,Kopuntsova, T. A , , Shandalova, L. P., Ihid., p. 114. 120.5) Shul’ts. M . M.. Peshekhonova. S . V., Lipets, T. F!., Ihid., p. 160. (206) Shul’ts, Ril. M . , Peshekhonova, S V., Parfenov, .4. I., Ivanova, E. A., Petrova, V. X . , Ihid., p. 104. (207) Shul’ts, M. M Peshekhonova. ? 11.. i. Shevina. G. P.. Ihid.. D . 120. (208) Shvaikn, 6. P,: Prots’enko, F. G., Zh. Analit. K h i m . 18, 410 (1963). (209) Simchen, A. E., J. Electroanal. Chem. 3, 286 (1962). (210) Siya, C. Y., Doleial, J., ZQka, J., Zh. Analit. K h i m . 16. 308 11961). (211) Smith, P., Biswas, M., Vosburgh, W.C., Anal. Chim Acta 28, 316 (1963). (212) Solyrnosi, F., Chemist-Anal:yst 52, 42 (1963). (213) Spaeth, E. E., Baptist, V. H., Roberts, PI., AKAL. CHEM.34, 1342 (1962). (214) Spencer, H. G., Lindstrom, F., A n a l . Chim. Acta 27,573 (1962). (215) Stern, K . H., J. Phys. Chem. 57, 893 (1963). (216) Stock, J. T., Analyst 87, 908 (1962). 1217) Stock. J. T.. Fill. hl. A.. Lab. PracLice 10, 302 (1961). ‘ 1218) StrBfelda, F.. Collection Czech. \ -
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(219) SuchornelovB, L., ZQka, J., J. Electroanal. Chem. 5,57 (1963). (220) Surash, J. J., Hercules, D. M., J. Phus. Chem. 66, 1602 (1962). (221) Swensen, R. F., Keyworth, D. A., ANAL.CHEM.35,863 (1963). (222) Takahashi, T., Bunseki Kagaku 8,661 (1959). (223) Ibid., 9, 220 (1960). (224) Ibid., p. 224. (225) Ibid., p. 561. (226) Ibid., p. 56.5. (227) Ibid., p. 921. (228) Takahashi, T., Siki, E., Sakurai, H., J. Electroanal. Chem. 3, 373 (1962). (229) Takhashi, T., Sakurai, H.. Ibid.. p. 381. (230) Takeuchi, Y.,J. Chem. SOC.Japan, Pure Chem Sect. 82, 1644 (1961). (231) Teze, M., Schaal, R., Bull. SOC. Chim. France 1962, p. 1372. (232) Toni, J. E., ANAL. CHEM.34, 99 (lW21 \----,
(233) Tshernyak, R. S., Zavodsk. Lab. 27, 536 (1961). (234) Underwood, A . L., Howe, L. H., ANAL.CHEM.34.692 11962). (235) Van Rysselberghe; P., /. Electroanal. Chem. 4, 314 (1962). (236) Vulterin, J., Zj.ka, J., Talanta 10, 891 (1963). (237) Vydra, F . , Pfibil, R., Zbid., 5, 44 11960). (238) Ihid., 8, 824 (1961). (239) Ihid., 9, 1009 (1962). (240) Watt, W.J., Blander, M., J. Phys. Chem. 64,729 (1960). (241) Williams, T . R., Custer, J., Talanta 9, 175 (1962). (242) Williams, T. R., Lautenschleger, M., Ibid., 10, 804 (1963). (243) Wilson, A . M., Munk, M. E., .ANAL. C H E M . 34,443 (1962) (244) U’imer, D. C., Ibzd., p. 873. (24.5) Winefordner, J. D., Davison, G. A,, Anal. Chim. Acta 28, 480 (1963). 1246) Winefordner. J. D.. Tin. M.. ANAL. CHEM.35,382 (1963). (247) Wise, R. N . , Guerry, D., Ihid., 34, 719 (1962). (248) Witwit, A. S., Magee, R. J., Anal. Chim. Acta 27,366 (1962). (249) Wolf, S., Mobus, B., Z . Anal. Chem. 186, 194 (1962). (250) ZLka, J., Zavodsk. Lab. 27, 1075 (1961). I
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