V O L U M E 2 8 , NO. (136) (137) (138) (139)
4,
A P R I L 1956
671
Parks, T. D., Al;al. Chim. Acta 6,553 (1952). Parks, T. D., Lykken, L., ANAL.CHEM.22, 1503 (1950). Ibid., p. 1505.
Parks, T. D., Smith, 0. D., Radding, S.B., A n a l . Chim. Acta
10, 485 (1954). (140) Pecsok, R. L., Juvet, R. S.,Jr., J . Am. Chem. Soc. 77, 202 (1955). (141) Pelt, J. G. van, Keuker, H., Chem. Weekblad51, 97 (1955). (142) Peshkova, \-. AI., Gallai, Z. A , , Vestnik Moskoti. Cnii.. 9 ( S o . IO), Ser. F i z . M a t . i Estestcen. X a u k , S o . 7 , 73 (1954). (143) Peshkova, I-.ll.,Gallai, Z. A., Zhur. A n a l . K h i m . 7 , 152 (1952). (144) Ibid., p. 171 (in English). (145) Peters, E. D., Jungnickel, J. L., .&R-AL. CHEx 27, 450 (1955). (146) Pickles, D., Washbrook, C. C., Analyst 78, 304 (1953). (147) Popel, 9.A , , Alarunina, A. T., Zaaodskaya Lab. 16, 658 (1950). (148) Pyibil, R., Doleaal, J., Simon, V., Chem. Listy 47, 1017 (1953). (149) PTibil, R., Matyska, B., Collection Czechoslov. Chem. Conimuns. 16, 139 (1951). (150) PFlbil, R., Roubal, Z., Chem. L i s t y 47, 189 (1953). (151) l’hbil, R., Vicenova, E., Ibid., 46, 535 (1952) : Radiometer Polarographies 2, 99 (1953). (152) PFibil, R., Zabransky, Z., Chem. Listy 46, 16 (1952); Radiometer Polarngraphics 1, 122 (1952). (153) Reilley, C. K.,Cooke, W. D., Furman, N. H., ANAL.CHEM. 23, 123 (1951). (154) Richter, H. L., J r . , Ibid., 27, 1526 (1955). (155) Rowley, K., Swift, E. H., Ibid., 26, 373 (1954). (156) Ibid., 27, 818 (1955). Ibid., 25, 660 (1953). (157) Rulfs, C. L., Nackela, A. d., (15s) Saikina, XI. K., Toropova, V. F., T r u d y Komissii Anal. h-him. A k a d . .Yauk, S . S . S . R . , Otdel Khim.X a u k 4 ( 7 ) , 141 (1952). (1.59) Samson, S.,S a t u r e 172, 1042 (1953). (160) Samson, S.,Zschuppe, H., Chem. Weekblad 50, 341 (1954). (161) Sandberg, B.,Sbornfk Mezindrod. Polarog. Sjezdu Praze, 1st Congr. 1951 Pt. I, 227. (162) Scholten, €1. G., Stone, K. G., ASAL. CHEM.24, 749 (1952). (163) Seagers, W. J., Friediani. H. A . , Ibid., 26, 1098 (1954). (164) Sekerka, I., S’orlicek, J., Chem. Listy 47, 512 (1953). (165) Shinagawa, ll., Matsuo, H., Isshiki, S., J a p a n Analyst 3, 199 (1954). (166) Shinagawa, AI., lfatsuo, H., Sunahara, H., Ibid., 3, 204 (1954). (167) Sifre, G., Mem. poudres 35, 373 (1953). . H E x 24, 915 (1952). (168) Simon, V., A s . 4 ~ C (169) Simon, Y., Grim, V., Chem. Listy 48, 1774 (1954).
REVIEW OF FUNDAMENTAL DEVELOPMENTS IN
(170) Simon, \-., Sekerka, I., Dolezal, J., Ibid.. 46, 613 (1952); h . 4 ~ . C H E Y . 24, 915 (1952). (171) Songina, 0. A . , Trudy Komissil A n a l . K h i m . Akad. .Vauk S.S.S.R., Otdel. K h i m . N a u k 4(7), 116 (1952). (172) Songina, 0. A., Voiloshnikova, A. P., KoalovskiI, lf. T., Izrest. A k a d . S a u k Kazakh. S.S.R., No. 118, Ser. Khim., KO.6 , 69-77 (1953). (173) Songina, 0. A., Voiloshnikova, -4.P., Kozlovskii, 31. T., Zzrest. A k a d . S a u k Kazakh. S.S.R., KO.101, Ser. K h i m . , No. 4, 80 (1951); I b i d . , S o . 3 (1949). (174) Stock, J. T., Metallurgia 46, 209 (1952). (175) Stone, K. G., ABAL.CHEY.26, 396 (1954). (176) Stone, K. G., Scholten, H. G., Ibid., 24, 671 (1952). Kolthoff, I. l I . , Ibid., 25, 1050 (1953). (177) Stricks, W., Kolthoff, I. lI.,Tanaka, K.,Ibid., 26, 299 (1954). (178) Stricks, K., (179) Sundaresan, AI., Karkhanarala, 31. D., Cw-relit Sei. (India) 23, 258 (1954). (180) Talafant, E., Sevela, LI., Chem. L i s t y 46, 182 (1952). (181) Tomicek. O., Cihalek, J., Dolezal. J., Simon, V., Zj.ka, J., Ibid., 46, 710 (1952). (182) Tutundzhic, P. S., Anal. Chim. Acta 8, 168. 182 (1953). (183) Tutundzhic, P. S..AIladenovic, S.,Ibid., 8, 184 (1953). (184) Usatenko, U. I., Bekleshova, G. E., Gkrain. K h i m . Zhur. 20, 690 (1954). (185) Vasil’ev, A. XI., Popel, A. .4.>T r u d y Koiizissil Anal. Khirn. Akad. ,Yauk S.S.S.R., Otdel I i h i m . S a u k 4 ( i ) , 126 (1952). (186) Warshowsky, B., Shook, T. E., Schantz. E. J.. AXAL. CHEM. 26, 1051 (1954). (187) Watt, J., Ibid., 27, 1036 (1955). (188) Weissman, K.,Shoenbach, E. B.. Alr.niteal. E. B., J . Uiol. Chem. 187, 153 (1950). (189) Khitlock, E. A,, Lab. Practice 1, 73 (1952). (190) Willits, C. O., Ricciuti, C., - ~ B A L . CHElr. 23, 1712 (1951). (191) Wilson, R. F., Lovelady, H. G.. Ibid., 27, 1231 (1955). (192) Wise, W. S., Schmidt, 5 . O., Ibid., 27, 1469 (1955). (193) Woodson, A. L., Johnson, B. H., Cooper, S . R., Ibid., 24, 1198 (1952). (194) Yasumori. Y., Bull. Chem. SOC.J a p a n 24, 107 (1951). (195) Yoshida, K., Kurihara, 31., J a p a n Analus! 1, 89 (1952). (196) Zagorski, Z., Wiadomofci Chem. 7, 193 (1953). (197) Zan’ko, A. A,, Panteleeva, L. I.. Trudg Komissii A n a l . Khim., A k a d . .Yauk S.S.S.R.. Otdel. K h i m .Yauk 4 ( 7 ) . 135 (1952). (198) Zuman, P., Prochaaka, Z., Chem. Listg 47, 357 (1953); ‘Leybold Polarog. Ber. 1, KO.6. 29 (1953). (199) Zweig, G., Block, R. J., J . Dairu Sci. 36, 427 (1953).
I 1 I
I Potentiometric Titrations I
I
T
[
CHARLES
N. REILLEY
1
Department
o f Chemistry,
University of N o r t h Carolina, Chapel H i l l ,
HIS paper attempts to summarize the chief trends in the development and application of potentiometric titrations since the time of the prior review in the series by Furman (60). Elving (44)has reviexed the current status of analysis by titration and summarized several trends in development and application with respect to reactions, titrants. measurement of titrants, media for titration, and detection of the equivalence point. Langford (89) covers various methods applicable in the electroplating industry. Codell, Norwitz, and Rlikula (68) have reviewed the new methods of titanium alloy analysis. The methods for the determination of free chlorine have been surveyed by Whitlock (174). West ( 1 7 3 )has reviewed the topic of titrations in anhydrous solvents. Katers, Berg, and Lachman (176) have surveyed the scope of potentiometric titrations in pharmaceutical control.
N. C.
THEORETICAL DEVELOPMENTS
Interpretation of Polarization Curves. On the basis of Sernstian equilibria and kinetics, Jordan ( 7 1 ) interpreted the reversibility and irreversibility of simple electrode reactions in terms of two competing rate processes. Jordan derived a generalized wave equation for the current-voltage curves obtained in “hydrodynamic voltammetry” for the case where the competing rate processes are mass transfer and electron transfer: 2 =
rnox h
+
x
il nzox
K .fox
frcd
inred
+
where il is the limiting current (amperes), m denotes mass transport coefficients (centimeters per second) for the oxidized and
ANALYTICAL CHEMISTRY
672 reduced species, f denotes the activity coefficients, and K corresponds to the ratio ( k o x l k r e d ) of the first-order rate constants (centimeters per second) for the forward and reverse step of the reaction ked
Red _J OX +ne k ox The prediction and interpretation of the form of the curves obtained in bimetallic potentiometric titrations have been pointed out by Coursier ( 3 1 ) through the use of polarization curves. Four cases are distinguished: (1) Both the oxidized and reduced forms of the two systems are electroactive a t the two electrodes, (2) both systems have only one electroactive form, ( 3 ) the titrant has only one electroactive form, and (4)the system titrated has only one electroactive form. Kies ( 7 9 ) derived a theoretical equation for the intensity of current as a function of added reagent during a dead-stop titration for reversible systems. Polarization curves were used by Coursier (30) to explain certain effects which occur in the neighborhood of the equivalence point in a potentiometric titration, such as slow attainment of an equilibrium potential. Duyckaerts (42) has presented an exeellent summary of recent developments in the interpretation of electrotitrimetric methods in terms of polarization curves. Kolthoff (81) has reviewed the relationships among voltammetry, potentiometry, and amperometry and has presented equations and data to illustrate these relationships quantitatively. Charlot ( 2 5 ) has also pointed out the significance of polarization curves. Piontelli and others (115) have described exact methods for measuring polarization voltages. Adams ( 2 ) extended the technique of controlled currentscanning polarography to electrometric titrations. The dropping mercury electrode was employed for the titration of cadmium with ethylenediaminetetraacetic acid [(ethylenedinitrilo)tetraacetic acid]. I n this method a small constant current, of about lpa., was applied between the calomel and dropping mercury electrodes. The resulting potential drop across the two electrodes was measured during the course of the titration, with the break occurring just prior to the equivalence point. Tegze (155) has studied titrations in which the end point is indicated by measuring voltage a t constant current. Included in his study were argentometric titrations with silver electrodes; neutralization titrations with hydrogen, quinhydrone, and antimony electrodes; oxidation-reduction titrations; and reactions involving complex formation. A new principle of end-point detection termed “chronopotentiometric” has been described by Reilley and Scribner (124). The method is based upon measurement in quiet solutions of the “transition times” for a species during the course of a titration. I n operation, a constant current is applied suddenly across an electrode-solution interface. The resulting potential then progresses rapidly to the decomposition potential of the species, remains there until the species a t the interface has been depleted entirely, and finally moves to the decomposition potential of some other species or the solvent. The square root of the time (transition) required for complete depletion is directly proportional to the concentration of the species. The titration curves are straight lines essentially analogous to amperometric titration curves. The method is particularly applicable to titrations of small volumes and to situations where stirring is undesirable. Potential-pH Diagrams. Sillen (140) has discussed the usefulness of redox diagrams of which potential-pH diagrams are a special case. These diagrams summarize a large number of competing equilibria into a readily digestible diagram whereby one may obtain quickly a clear picture of how the various equilibria interact. Charlot (26) has also discussed application of potential-pH diagrams and polarization curves in analytical chemistry.
Determination and Use of Equilibrium Constants. Vanderbelt, Henrich, and Vandenberg ( 1 6 4 ) have compared the determination of pK: values by electrometric titration and ultraviolet absorption methods. These methods are in good agreement. The titration method is more rapid, especially when two or more ionizable groups are present in a molecule. When the pK; values are close-e.g., adjoining pH units-the absorption method is extremely difficult to apply. The absorption method is not so generally applicable, as appreciable spectrum changes are not always obtained, especially in the case of some carboxyl derivatives. The absorption method is the more desirable for very large or very small pKi determinations where pH or pOH values are near unity. I t is also useful in studying materials of low relative solubility. -4pparent dissociation constants determined within i.O.05 pK‘ unit by potentiometric titration may be employed in qualitative organic analysis on a milligram basis as described by Parke and Davis (111). A chart of p K i values for 573 compounds is given. The hydrolysis constants of 12 n-primary amines in 22% ethyl alcohol weie determined by Slabaugh and Cates (146) from potentiometric titration data. Kieffer and Rumpf (78) determined the dissociation constants and structures of 14 phenolic compounds by potentiometric and spectrophotometric methods. The formation of ion pairs becomes particularly prominent in media of lox- dielectric constant, often resulting in inaccurate inflection points in the potentiometric titration of acids and bases in nonaqueous solvents. Troublesome salt effects on color indicators may also be expected. The physical nature of the ion pairs and the magnitude of their dissociation constants have been reviewed by Grunwald (56). Bates (8)has investigated the effect of dilution upon the pH of a buffer and has coined a unit, the ‘[dilution value,” 4pHm, the change in pH accompanying dilution of the buffer solution with an equal quantity of water. Two separate effects operate. The first is the effect of the acid-base equilibrium of water upon the buffer equilibria, causing a shift toward a p H of 7 upon dilution. The second is the change in activity coefficients upon dilution. Bates (9) has published a comprehensive book covering the electrometric measurement of pH as well as properties and standardization of buffer solutions. The metal-chelating tendencies for a large number of chelating agents have been measured by the Bjerrum method. Lumb and Martell (94)have employed the method in the case of glutamic and aspartic acids. Kordatzki ( 8 3 ) has reviewed the measurement of oxidationreduction ( r H ) potentials. d series of “formal” potentials has been reported by Bock and Hermann (13) for the iron(III/II) aqueous system a t various strengths of perchloric, nitric, hydrobromic, hydrochloric, sulfuric, phosphoric, acetic, and hydrofluoric acids. The potential in 1.0r perchloric acid was 0.i47 volt us. the normal hydrogen electrode, and descending in the above order to 0.320 volt in hydrofluoric acid. Sillen (139) has reviewed his excellent previous work on the electrometric determination of the equilibria between mercury and halide ions. Studies of electrode potentials in fused potassium chloridelithium chloride media by Senderoff and Brenner (135) showed evidence for the formation of chloride complexes in the case of zinc, lead(II), iron(II), tin(II), and copper(1). Ricci (125) made a theoretical study of the relation of the inflection point of the p[Ag+] curve to the equivalence point and to the first appearance of a precipitate. He also considered the effect of the addition of ammonia. The Coulomb as a Primary Standard. Utilizing the fact that electrons are a most versatile reagent, Tutundzic (163) has proposed that the coulomb (by way of coulometric titrations) be considered as the “primary standard” for all volumetric standardizations. Statistical Studies. Linnig, Illandel, and Peterson (93) have described the statistical methods for use in studying the accuracy
V O L U M E 28, N O . 4, A P R I L 1 9 5 6 and precision of an analytical procedure through segregation into relative-type and constant-type systematic errors. Included is a discussion of the effect of proper choice of indicator based on a p H titration curve. APPARATUS
Instruments. The general field of automatic potentiometric titrations has been reviewed by Kimoto (80). Simon and Heilbronner (141) describe an automatic apparatus for microtitration of organic compounds. The rate of addition of titrant is governed by the rate of flow of mercury through a thermostated polarographic capillary and consequently can be made rather independent of the u w a l “thermometer” effect encountered in syringe delivery systems. With this apparatus a number of organic acids and bases were automatically titrated in methyl Cellosolve-water or dimethylformamide-water media and their dissociation constants determined. Richter (126) developed an instrument for performing automatic coulometric titrations using an amperometric end point. Wight and Burk (175) developed a technique for continuous recording of oxidation-reduction potential and pH changes in manometric vessels used in studies on dynamic biological systems. Eades and coworkei s ( 4 3 ) developed an automatic titrating and recording apparatus for microbiological assays, which can handle 225 samples consecutively and yield determinations on acids and bases within lY0 standard error. An apparatus for fully automatic determination of both ionization constants and enzj matic activity has been described by Seilands and Cannon (106). The kinetic analysis was acconiplished by following with time the volume of titrant necessary to maintain constant p H conditions in a slon ly reacting solution. The hydrolysis rate of triacetin by acetyl esterase of orange peel a t pH i . O O and the reduction rate of diphosphopyiidine nncleotide by lactic dehydrogenase of heart at pH 9.50 !%ereillustrative examples. A potentiometric device has been developed by Ingraham and Makower ( 6 6 ) to determine automatically the chronometric end point, which serves as an estimation of polyphenol oxidase activity. The principle is based on the enzymatic reaction in which o-quinone is continually produced and reacts in turn with an added amount of ascorbic acid. After a given length of time the ascorbic acid is entirely consumed and the potential change occurring between a platinum-saturated calomel electrode system electromatically shuts off the timing mechanism. The Beckman automatic titrator was adapted by Jones and Baum (70) for the automatic titration of chloride obtained from chlorinated organic compounds. An automatic trigger circuit useful for stopping the addition of titrant a t the end point has been developed by Carson ( 2 1 ) especially for use in coulometric titrimetry. Malmstadt and Fett (97) have developed an automatic differential potentiometric titrator which has special advantages for titrations where the end-point potential is not knoTm prior to titration or where the end-point potential changes rapidly with different titration conditions. Because the automatic differential titrator is not suited for titrations where the solution or electrodes reach equilibria very slowly, Nalmstadt and Fett (98) investigated the potential response characteristics of various indicator electrodes. For acid-base titrations they studied glass, antimony, platinum, platinum-107, rhodium, platinum-407, rhodium, and gi aphite indicator electrodes, with the platinum10% rhodium electrode exhibiting the most rapid response. This latter electrode also could be used advantageously in nonaqueous solvents-benzene-methanol or glacial acetic acid. Antimony electrodes were sluggish in their response but, v i t h appropriate corrections, good results were obtained. Hydrazine was titrated with standard iodate by the A n d r e w method using platinum-calomel. No lag in the electrode response mas detected Malmstadt and Fett also titrated successfully chloride with silver
613 nitrate and with mercuric nitrate. Cyanide was titrated with silver nitrate with no time delay in electrode response. Harwell (60) developed a stable electronic voltmeter for use in the accurate determination of the “chlorinity” of sea water by titration with silver nitrate. -4simplified dead-stop, magic-eye, end-point indicator has been developed by McCauley and Gresham (95) for routine Karl Fischer titrations. -2zero grid current vacuum tube voltmeter has been applied by Natelson (105) to the precise (10.002 pH unit) measurement of pH with the glass electrode. Hallikainen and Pompeo ( b 9 ) have devised a continuous electrometric titrator. Tubbs ( 1 6 2 )has described the use of two transparent templates, inscribed with concentric arcs, for rapid location of the inflection point of potentiometric titration curves. Parsons, Seaman, and Amick ( 1 1 2 )employed a small low-inertia motor for integrating the current-time relationship in coulometric titrations, thus avoiding the necessity for using regulated current supplies. They employed electrolytically generated ferrous ion, silver ion, and hydroxide ion for the titration of dichromate, chloride, and hydrochloric acid, respectively. Gerhardt, Lawrence, and Parsons ( 6 1 ) describe a precision coulometric titiator capable of carrying out coulometric titrations within O.1y0precision and accuracy, supplying constant currents up to 450 ma. Electrodes. A comprehensive study of residual currentvoltage phenomena of platinum electrodes resulting from sorbed hydrogen and formation and dissolution of platinous oxide films has been made by Kolthoff and Tanaka (86). Chemical pretreatments for minimizing these effects are described. Purdy, Burns, and Rogers (119) investigated in detail the senEitivity of the bromine-bromide potentiometric end point with particular regard to the factors contributing to the reagent blank in a coulometric titration. Janz and Taniguchi ( 6 9 ) have written a very comprehensive review on the preparation, stability, reproducibility, and standard potentials in aqueous and nonaqueous media of the silversilver halide electrodes. Gordon (54) describes a sturdy, easily resurfaced silver indicator electrode useful in halide determinations. Achiwa ( 1 ) suggested the use of metal-metal sulfide indicator electrodes in neutral titration of metal ions. Hubbard ( 6 3 ) has studied the temperature effect on electrical resistance and voltage errors of glass electrodes. Glass electrode failures were attributed to low hygroscopicity of the glass, excessive wall thickness, poor chemical durability, high electrolyte concentration, and inhibiting films. Heyn and Bergin (61) attempted without success to make a glass electrode which would function in liquid ammonia systems. Carson and hlichelson (22) investigated the effect of radioactivity on the p H response of glass electrodes. N o effect was observed after exposure to 200 curies per gallon of 0-activity, 300,000 r. per hour of ?-radiation, or 0.5 mc. per gallon of aactivity. hiantzell (99) has investigated the effect of electrical polarization on the precision of p H measurements made with the antimony electrode. Rabinovich and Gorbunova (120) investigated the potential and temperature coefficient of the antimony electrode in the intervals p H 2 to 12 and 20” to 50” C. An effect caused by citric acid or boric acid was noted. Rabinovich and Kurovskaya (121) described the preparation of a rugged platinum electrode made simply by metallizing the glass in a flame with a special mixture containing chloroplatinic acid, rosin, alcohol, and boric acid. -4metallic mercury electrode covered with solid mercurous acetate was found by Scarano and Ceglie (169) to be useful as an indicator electrode for neutralization reactions in glacial acetic acid solvents. Sinha (144) discusses the possible application of ion exchange
674
ANALYTICAL CHEMISTRY
resin membrane electrodes for p H measurements in the absence of other cations. Fuji and Ishikawa (49) have investigated the preparation and use of palladium hydride electrodes for p H measurement. A mean error of only 0.001 p H unit is claimed in simple systems. Kunze (86) has proposed the use of a chromic chromate, Crz(OHjrCr04, electrode as an indicator electrode, especially in alkaline qolutions where the quinhydrone electrode is unsatisfacto1 y. A paper by Ohlweiler and Meditsch (107)describes the general ri,efnlness of the glass electrode as a reference electrode in odation-reduction titrations. Porous glass and ion exchange membranes mere adapted by Carson, Michelson, and Koyama ( 2 3 ) for use in salt bridges to obtain greater mechanical stability. smaller solution flow, and less electrical resistance. Brunisholz ( 1 7 ) has described a salt bridge and reference electrode of particular use in potentiometi ic titrations. Lamoen and Boreten (88) described the use of a platinized platiriuni indicator electrode and a shielded bright-platinum reference electrode for potentiometric titrations with Karl Fischer reagents. APPLICATIOYS
Analysis Based upon Measured Potentials. An interesting use of potential measurements was desrribed by Onaka (108). B y employing the cell Ag/( molten steel)//electrolyte, H2/Ag the potential difference was measured and correlated directly with the oxygen content of the molten steel. An oxygen content of 0.06570, for example, corresponded to a potential of 160 mv. Kahlweit, Strehlow, and Hocking ( 7 2 ) found that an electrolytic cell of the type Electrolyte a in H20
1 electrolyte b in oil
electrolyte a in HlO
exhibits an electromotive force indicative of ion exchange behavior. With electrolyte a as different concentrations of potassium chloride, and electrolyte b as the potassium salt of phenyl quinoline carbonic acid (in quinoline), the system behaved as a cation exchanger. Solvolytic rate constants were obtained by Kwart and Wilson (87) with an apparatus which automatically followed by potentiometric means the course of the reaction. Marshall (100) determined the solubility of uranium trioxide in aqueous sulfuric acid a t elevated temperatures, 150" to 290" C., by sampling the equilibrated solution a t the desired temperature, cooling t o 26' C., and comparing the pII of the sample with control pH data. The precision pH measurements were made within f0.004p H unit, using a vibrating reed electrometer. The chloride ion content in a solution n-as determined by Chanin ( 2 4 ) by measuring the potential of a silver-silver chloride electrode immersed in the solution and comparing the measurement with a calibration curve. Carbon dioxide in air was estimated by Kauko and Ice1 ( 7 6 ) using a concentration cell containing quinhydrone. Through one half cell the gas to be analyzed was bubbled. Pure carbon dioxide was bubbled through the other. By running the gas over iodine pentoxide or Hopcalite 11, carbon monoxide could also be determined, C u t s and Burianac ( 3 4 ) followed the concentration of traces (0.003 to 0.5 mg. per liter) of hydrogen sulfide in hydrogen by passing the gas mixture into an absorption device containing a very dilute iodine solution. The content of hydrogen sulfide was determined from the difference in electrode potentials before and after absorption by means of a calibration curve. Frisque and Meloche ( 4 6 ) have described a mathematical method for determining the concentrations of two weak monobasic acids in a mixture in the case where the pK's of the acids are
so close together that only one b e a k is observed in the p H titration curve. An antimony microelectrode was used by Kamienski, Bylo, and Waligora ( 7 3 ) for detecting 10-2 to l O - 5 X quantities of various acids and bases as they were eluted from an alumina column. The logarithmic relationship between the electrode potential and concentration allowed easy detection of minute quantities. The antimony electrode was also found by Kamienski, Puchalka, and Dolinski ( 7 4 ) to be useful in following the elution of stearic and oleic acids from silica gel columns by a benzene-alcohol eluent. Acid-Base Processes. AQCEOUS. Van Wazer, Griffith, and McCullough ( 166) have described a pH titration procedure for the determination of orthophosphates, polyphosphates, and total phosphorus pentoxide. Titration with base consumes two hydrogens from orthophosphate and end-group hydrogens on polyphosphates. Addition of silver nitrate frees the third proton of orthophosphate t'o allow determination of orthophosphate. Titration, after hydrolysis in hydrochloric acid to convert polyphosphates to orthophosphates, allows determination of total phosphorus pentoxide. A rapid volumetric method for mercury proposed by Palit and Somayajulu (110) consists of conversion to neutral mercuric* oxide, addition of excess potassium iodide or sodium thiosulfate, and subsequent acidimetric titration of liberated alkali. They also recommend mercury salts as primary acidimetric standards. Hall and St,one (58)have proposed the use of 4-aminopyridine a i a standard in acidimetry. It is easily purified by recrystallization from toluene or benzene and is a moderately weak base (dissociation constant = 1.3 X Larson and Henley ( 9 0 ) determined with extreme sensitivity low alkalinity or acidity in rain water. Extrapolation to 1 X 10-7 mole ( H + ) per liter was necessary to obtain a precise equivalence point. Warner and Raptis (17'1) determined formic acid in the presence of acetic and other organic acids by first separating the formic acid by azeotropic distillation with chloroform and subsequently titrating recovered formic acid directly with standard base. Day and others (36) passed an aqueous solution of uranyl sulfate, nitrate, chloride, perchlorate, and dichromate through a cation exchange resin (on hydrogen cycle) and titrated the acid effluent with standard base t o determine t'otal anion concentration. Zall, Kagman, and Ingber (179) proposed a rapid voliimetric acid-base titration for analysis of boiler compounds consisting of sodium carbonate, disodium phosphate, and starch. Smelik and Habiger (147) report the applicat'ion of the antimony indicator electrode for the titration of dark liquors in the sulfate pulping industry. XOS.KJUEOVS.Brockmann and Meyer (16)developed a micromethod for determining the equivalent and molecular weight of weak organic acids and bases by means of potentiometric titrations in nonaqueous media. Fritz ( 4 7 )has outlined the general requirements of solvents and titrants for weak acids or bases. The most generally useful solvents for the titration of weak acids are dimethylformamide, ethylenediamine, butylamine, and alcohol-hydrocarbon mistures. For weak bases acetonitrile or chloroform allows differential titration. Wollish, Pifer, and Schmall (178) have pointed to the applicability of titration in nonaqueous solvents for the analysis of pharmaceuticals. The glass-calomel electrode system has been successfully used by Deal and Wyld ( 3 6 ) with alcoholic hydroxide titrants for the estimation of very weak acids, employing ethylenediamine and dimethylformamide alternatively as solvents to enhance the titration response desired. Wollish and others (177) have determined each component separately in APC (aspirin, acetophenetidine, caffeine) tablets, employing titration in nonaqueou9 media in the aspirin and acetophenetidine determinations. The neutralization equivalent of substituted fatty acids was
V O L U M E 2 8 , N O . 4, A P R I L 1 9 5 6 carried out by Radell and Donahue (183) in a benzene-methanol solvent using sodium methoxide titrant and antimony-calomel electrodes. Lithium chloride was added to the solvent to decrease the solution resistance. Anhydrous pyridine (157) served as the solvent for titrations of perchloric acid, formic acid, benzoic acid, and the ion exchange re.in, Zeo-Karb. The titrant was piperidine, ammonia, or diethanolamine dissolved in pyridine. -4 glass electrode was satisfactory for determining the end point. Glenn and Olleman (52) have adapted several known procedures for application to composite analysis of several types of coal hydrogenation products. Carboxylic acids and monohydric phenols were determined by sodium aminoethoxide titration in ethylenediamine, basic nitrogen compounds by percliloric acid titration in glacial acetic acid, primary and secondary amines and alcohols by acetylation with acetic anhydride-pyridine, primary and secondary amines only by acetylation followed by selective hydrolysis of 0-acetyl groups, and total active hydrogen with Grignard reagent. The use of the solvent acrylonitrile for the precise determination of small amounts (0.00170)of weak acids and bases has been reported by Owens and Alaute (109). The method is rapid and free of interference from atmospheric carbon dioxide, and standard glass-calomel electrodes may be used. Glenn and Peake (53) employed a glass-platinum electrode system for the titration of phenolic esters in ethylenediamine solvent. Carbon dioxide in ethanolamine was determined by Wagner and Lew (170). Cundiff and hlarkunas (33) replaced the saturated aqueous potassium chloride in a fiber-t,ype calomel electrode with a methanol solution saturated with potassium chloride in the nonaqueous perchloric acid titrat'ion used in the determination of nicot,ine, nornicotine, and total alkaloids in tobacco. Sulfuric acid yields two sharp breaks when titrated in acetonitrile solvent with morpholine. Critchfield and Johnson ( S d ) , ~ v h oinvestigated this effect, also found that mixtures of sulfuric :wid with hydrochloric or nitric acids conld be titrated in this manner to determine each component. Titrations of urea, thiourea, and various substituted guaniclines and nitroguanidines were effected by DeVries, Schiff, and Gantz ( 5 7 ) using diniethylformamide or trifluoroacetic acid as solvents with antimony-calomel and platinum-platinum electrodes, respectively. Of particular interest is the titration of nitroguanidine and thionren, materials which are not titratable in glacial acetic acid. An acetic acid-chloroforni solvent wa3 employed by Pifer, \Yollish, and Schmall (114) for the differential titration of ammonium or potassium acetate (stronger bases) in the presence of other niet:tl acetates. Streuli (151) found that basic copolymers of acrylonitrile may be titrated with perchloric acid when a mixture of nitromethane and formic acid is employed as a solvent. Seutralization titrations in anhydrous formic acid using hydrogen or quinhydrone electrodes was employed by Tomicelr xrid Vidner (160) for the determination of various organic bases. Siggia and Stahl (138) presented a nonaqueous method for determining aldehydes, \$-hicah consisted of adding a measured excess of unsymmetrical dimethylhydrazine to the sample, and, nfter the reaction is complete. back-titrating the excess with standard acid. The solvent employed was ethylene glycol or -~1etha1101. Jackson (6'8)determined primary fatty amines from the dif!i'wence betn-een the acid required for titration carried out in .chloroform in the absence and presence of salicylaldehyde. Greniillion (55) applied the use of acetic anhydride solvent in titrating veak primary and secondary amine bases whose Ka values in viater are 10-15 or larger. Acetic anhydride was also found useful in titrating the sulfuric acid catalyst in ethyl alcohol esterification mixtures. Fritz and Fulds (48) have investigated the titration of weak : bases in acetic anhydride-nitromethane solvent mixtures.
675 Excellent results were obtained with tertiary amines, including salts of purine, pyridine, pyridone, and thiazole types. Precipitation. Coulometric generation of silver ion was eniployed in the titration of thiourea and thioc,yanate by Sakanishi and Iiobayashi (103). The coulometric generation of silve:. ion was also applied by Lingane (.92) in the determination of chloride or bromide or iodide in amounts ranging from 0.2 to 10 mg. The Beckman automatic titrator was employed tu render the method automatic, with titrations completed in 1 to 5 minutes. h similar coulometric method was employed by Kowalkowski, Kennedy, and Farrington (84)in the deterniiiiation of iodide. V6ceEa (166) performed microdetei~minations of sulfur in organic compounds by combustion on a platinum contact, absorption on silver metal, and subsequent titration of the silver sulfate with iodide. Perchlorate (130) may be determined by reduction to chloride with a titanous, metallic aluminum mix under reflux and subsequent titration of chloride with silver nitrate. The potentiometric titration of micro quantities of halide3 (from organic halogen compounds) with silver nitrate, employing a silver-amalgamated silver electrode system, i3 described by Cogbill and Kirkland (29). A precise determination of chloride in plasma by direct titration with silver nitrate was accomplished by Dole and Thorn (41) using a differential potentiometric procedure. The silver-silver chloride electrodes were made in the usual manner by electroplating on platinum electrodes. The presence of bromide, thiocyanate, chlorate, cyanide, and iodide in argentometric determination of chloride was accommodated by oxidation with ceric sulfate and subsequent distillation in the procedure developed by hlahr and Otterbein (96). Free cyanide in the presence of sulfides was determined by Karchmer and Walker ( 7 5 ) by preliminary potentiometric titration of the sulfide with silver nitrate, followed by polarographic determination of cyanide. The dead-stop end point was employed by 3Iasten and Stone (102) for the successive argentometric titration of a threecomponent mixture of chloride, bromide, and iodide. Xntzel (6) has described the electrometric titration of mercury and silver with potassium iodide using a calomel electrode. Only iron(II1) interferes. Capitani and Gambelli (1,9) report the selective argentometric titration of cyanamide and dicyanodiamide. Ikeda and Komooka ( 6 4 ) added cadmium carbonate to eliminate interference of sulfide in argentometric titration of chloride. Use of an equal volume of ethyl alcohol minimized the effect of a considerable excess of sulfate ion. The titration of sulfate, based on addition of excess lead and back-titration with ferrocyanide, has been proposed by Igasyan ( 3 ) . Tananaev, Glushlrova, and Seifer (154) titrated lanthanum solutions potentiometrically with standard potassium ferrocyanide on the principle of precipitating KLa [Fe(CS),] . 'iHzO, which has a solubility of 2.28 to 2.76 X lo-' mole per liter. A method proposed by Teodorovich and Leushina (156) uses the precipitation of copper ions upon addition of potassium ferricyanide to estimate copper. Vogel (167) employed a combined distillation-titration to determine fluoride in the presence of boron, beryllium, titanium, aluminum, or thorium. The fluoride, distilled as HpSiF,, is titrated with standard uranyl solutions in the presence of the potassium salt of sulfanilic acid as buffer, utilizing the precipitation of KUFE. Sodium ion was titrated in milligram amounts in 85 to 95yc aqueous ethyl alcohol by Tomicek and Pulpan (158), using uranyl zinc acetate titrant and an indicator electrode of Jena G 20 glass. Potassium in smaller concentrations than sodium did not interfere. Wittman (176) determined ferrous iron by precipitation with ferricyanide. Complexation. The use of chelating agents, such as ethylenediaminetetraacetic acid, as reagents in titrimetric analysis
676 promises to be one of the most profitable new developments in analysis. Such agents lead t o sharp end-point breaks because they combine with the metal ions in a 1 to 1 ratio, thereby eliminating the undesirable formation of lower complexes prior to the end point and the dissociation of higher complexes near the end point. The chelating effect also enhances the stability of the complex and causes a larger break in the end point. Martell and Chaberek (101) have described these influences and discussed several methods for detecting the equivalence point in these titrations. An excellent introduction t o the scientific thinking which led eventually t o the development of ethylenediaminetetraacetic acid is the recent lecture to the Society for Bnalytical Chemistry by Schwarzenbach (132). Schwarzenbach (133) pioneered the development and application of such reagents and has recently collected the pertinent current literature into book form. Blaedel and Knight (12) have described the purification and properties of a primary standard grade of ethylenediaminetetraacetic acid. .4 0.01M solution of the disodium salt was found to change by less than 0.0570 in titer after storage in polyethylene bottles for 5 months. Siggia, Eichlin, and Rheinhart (137) developed a potentiometric titration procedure for analyzing chelating agents, metal ions, and metal chelates as well as mixtures of components, with an accuracy of 117,. Selective titrations tvere effected by proper choice of electrode (mercury plated on platinum, silver, or bright platinum), solution conditions (pH, buffer type), and titrant. I n this manner iron, copper, mercury, zinc, lead, manganese, calcium, magnesium, nickel, and cobalt could be determined alone. By employing metal ions as titrants, ethylenediaminetetraacetic acid, N,N-di(p-hydroxyethyl)glycine, or nitrilotriacetic acid-or mixtures of ethylenediaminetetraacetic and nitrilotriacetic acids-could be estimated. Chilton and Horton ( 2 7 ) describe an improved acidimetric determination of fluoride, whereby the titration of a neutral solution of fluoride with aluminum ions exhibits an abrupt decrease of pH a t the stoichiometric end point. The method is applicable in the range 0.1 t o 3.5 mg. of fluoride per ml. of water and gives a standard deviation of less than 0.27, with a recording p H meter. Sodium fluoride also was titrated with aluminum salts by Talipov and Teodorovich (163) using a quinhydrone electrode. Oxidation-Reduction. FERROUS XETHODS. I n the determination of chromium, iron, and silica in chromite ores, Zivanovic (180) titrated the chromium (after oxidation to dichromate) with standard ferrous and the iron (after reduction to ferrous) with dichromate. Trivalent and total cobalt can be determined in the presence of excess tungstate, molybdate, and iron by the method of Baker and McCutcheon ( 7 ) , by introducing excess ferrous ion and back-titrating with dichromate. Total cobalt is determined by oxidation of cobalt t o cobalt(II1) hydroxide with sodium perborate prior to addition of ferrous iron. Iron(I1) perchlorate can be used in glacial acetic acid for the titration of oxidants, chromium trioxide, and sodium permanganate, by the method of Hinsvarlr and Stone (62). CHRoarous. Standard chromous chloride was employed by Bottei and Furman (14) for determination of anthraquinones, and nitro, nitroso azo, and acetylenic compounds using platinumcalomel electrodes. Snthraquinone could be determined directly, while the other compounds required an excess of chromous ion with subsequent back-titration with standard ferric alum solution. TUXQSTEN(V) AS REDUCTAST. Tungsten(V) prepared by electrolytic reduction of tungstate in 1 O S hydrochloric acid is sufficiently stable under proper storage conditions t o serve as an effective reducing agent. Tourky, Issa, and hmin (161) employed this titrant for the determination of chromium, iron, copper (in hydrochloric acid), and iodate.
k+
ANALYTICAL CHEMISTRY
URAVOCS -4s A REDCCTAST. Electrolytically generated uranous ion was employed by Shults, Thomason, and Kelley (136) for the automatic coulometric titration of dilute ceric sulfate (0.1 to 2 mg.) and dilute potassium dichromate (17 to to 260 y) solutions. Quadrivalent uranium, prepared by passage of uranyl acetate (in 4.11 hydrochloric acid) through a silver reductor, was found by Belcher, Gibbons, and West (10) t o be one of the most stable titrants for the direct titration of ferric iron. I R O N (II)-ETHYLESEDIABIISE TETRAaCETATE AS .4
REDUCTANT.
Belcher, Gibbons, and West (11) studied the effect of E D T A on the redox potentials of the iron(III/II) and copper(II/I) systems and found that the potential of each system was markedly reduced, being 0.12 and 0.13 volt us. N.H.C., respectively With the resulting enhancement of the reducing power of the lower valence state (resembles titanous), a variety of oxidants could be successfully titrated. Silver was determined reductometrically by Pfibil, Doleial, and Simon (118) by titrating with iron(11)-ethylenediamine tetraacetate. CYAKIDE.The reaction between elemental sulfur and cyanide ion has been applied to the volumetric determination of sulfur in acetone extracts by Skoog and Bartlett (145). CERICTITRATIOSS. Dilts and Furman (39) employed coulometric generation of ceric ion to determine ferrocyanide in the 1.7 to 62 Feq. range with an over-all accuracy within +0.40%. Titanium and mixtures of titanium and iron were determined coulometrically by Dilts and Furman (40) by initial reduction in a Jones reductor and subsequent oxidation Kith electrolytically generated ceric ion. Small quantities of uranium( IV) in the presence of iron were determined by Hahn and Kelley ( 6 7 ) through oxidation with standard sulfatocerate using a platinum reference and gold indicator electrodes. Ceric sulfate was found by Saeki and Sakano (128) to be an effective titrant for the direct titration of 2-methyl-1,4-naphthoquinone and hydroquinone. Sodium acetate causes low results. The usefulness of the titration of antimony(II1) with ceric ion in the presence of iodine monochloride catalyst has been confirmed by Takagi and S a k a n o (166). Platinum-rhodium or tantalum us. silver gave well defined end points. Laboratory preparation and standardization of cerium(1V) perchlorate for routine applications are described by Smith (148). DIcHRohfATE. hlixtures of quinone and hydroquinone can be analyzed for both species by the method of Brauer and Staude (15). Quinone is selectively titrated by thiosulfate to a suitable potentiometric end point. After the reaction product is run through an anion exchange column to remove the quinone monosulfurate, the hydroquinone in the effluent is titrated with dichromate. Organic substances whose carbon atoms are individually attached to oxygen atoms-e.g., carbohydrates-can be determined with dichromate, using the heat of dilution of concentrated sulfuric acid in place of eyternal heating, according t o Launer and Tomimatsu (91). TE ~ I E T H O D STellurium . in dilute concentrations (3 X 10-5M) has been determined by Amin, Issa, and Issa ( 6 ) through potentiometric titration of tellurite with 10-4Alf potassium permanganate. Issa and Awad (66) titrated tellurium(1V) with alkaline permanganate and obtained a potential break of about 180 mv. a t the end point. The estimation of bivalent lead ions based on their oxidation to the quadrivalent state by alkaline permanganate (forming lead tetroxide and manganese dioxide) has been proposed by Issa, Issa, and Abdul (67). Singh and coworkers (142) found oxidation with alkaline permanganate useful for the analysis of iodide, iodate, cyanide, methanol, glycerol, phenol, and salicylic acid. FERRICYANIDE METHODS. Diehl and Butler (38) replaced
V O L U M E 2 8 , NO. 4, A P R I L 1 9 5 6 ammonia with ethylenediamine in the titration of cobalt(I1) with standard potassium ferricyanide. -1larger potential break at the end point results. Cobalt and manganese can be determined successively in the sample by this procedure. A volumetric method for hydrogen peroxide, based on its oxidation to oxygen by potassium ferricyanide in strongly alkaline solution, has been investigated by Vulterin and Zyka (168). Hydrazine, hydroxylamine, and isonicotinoyl hydrazide were determined by Vulterin and Zyka (169), using direct titration with potassium ferricyanide in alkaline media. Ferricyanide in excess iodide was titrated by Burriel, Conde, and Jimeno (18), using mercurous ion as an air-stable reductant. UROMINATIOXS.Aichenegg and Haynes ( 4 ) applied a direct bromination titration t o determine o-cresol, 4-chloro-2-methylphenol, or 2-methylphenouyacetic acid using a dead-stop end point. A volumetric method for the analysis of synthetic acetic acid derivatives was developed by Capitani and Imperiale ( 2 0 ) . \%yl acetate was determined by bromination at 0’ in acidic aqueous solution by the bromide-bromate method. Unsaturated aldehydes (86) can be determined even in the presence of satnrated aldehydes by diiect potentiometric titration with bromine i n absolute methanol. IODISEA \ D IODINE METHODS. Schreiber and Cooke (1.31) scaled down the ordinary coulometric titration techniques to 30 pl.-of solution. With this technique niicrovolumes-e.g., 0.1 to 7 y of arsenic, for euample, could be titrated n i t h electrlcally generated iodine with an accuracy of 2 to 57,. .1 platinum w r e indicator electrode v s . S.C.E was used for deterting the end point. Externally generated chlorine, bromine, and iodine were employed by Pitts, DeFord, illartin, and Schmall(116) for the coulometi ic titration of arsenite in 1-m.e.q. quantities. Excellent results were obtained using platinum-calomel electrodes. Chloiamine-B has been proposed by Singh and Singh (143) for the indirect determination of oxidants which liberate iodine from potassium iodide. The chloramine-B is used for titrating the liberated iodine. Rowley and Swift ( 1 2 7 ) titrated oxidizing agents by the indirect method of liberating iodine from iodide with the ouidizing agent, adding a known quantity of thiosulfate to reduce the liberated iodine, and finally titrating the excess thiosulfate with coulometrically generated iodine. Press and hlurray ( 1 1 7 ) have titrated sulfide ion in solution by coulometric generation of iodine, employing an amperometric end point. KARLFISCHER METHODS. A substantial gain in stability of Karl Fischer reagents was achieved by Peters and Jungnickel 1(11.3) by substituting methyl Cellosolve for methanol. The addition of ethylene glycol to the pyI idine also improved the md-point response, Sneed, .Liltman, and Mosteller ( 1 4 9 ) investigated the effect of tetraethyllead, aromatics, olefins, mercaptans, and oxidation inhibitors present in aviation gasoline on the determination of the u-ater content. Only mercaptans in usually large concentrations seemed to interfere. Reed (123) has described a procedure for determining moisture in refrigerant-oil mixtures by the Karl Flscher method. IODATE METHODS. Stone (150) found that iodide was quantitatively oyidized to iodine by iodate if chloroform was added t o *dissolve the iodine. The dead-stop end point was useful for practical titrations. HYPOCHLORITE. Uranium was determined in the presence of titanium and beryllium by Sekerka and Vorlicek (IS,$), who precipitated the uranium with ammonia in the presence of ethylenediaminetetraacetic acid, and titrated the ammonia in the precipitate with standard calcium hypochlorite. CHLORATE. Erdey and Mazor ( 4 6 ) determined vanadium by reduction tQ vanadium(I1) in a cadmium reductor and titration
611 with standard potassium chlorate t o vanadium(ii1). Iodineiodide catalyst was added to eliminate the necessity for heating. NITRITE. Sulfate has been determined by Keller and RIunch ( 7 7 ) by a procedure whereby the sulfate is precipitated from an alcohol-water solvent as benzidine sulfate. The precipitate is then dissolved and titrated directly with standard sodium nitrite using a platinum-calomel or tungsten-calomel electrode system. I~OXAQCEOUS SYSTEXS. Tomicek, Stodolova, and Herman (169) performed reductometric titrations in glacial acetic acid. The reducing power of the titrants, thiosulfate, vanadyl acetate, and arsenious trichloride, could be varied by addition of strong acid or base. Bromine, chromic oxide, permanganate, iodine monochloride, bromate, iodate, chloramine-T, and lead tetraacetate were determined. ELECTROLYSIS. Xakano, Nonaka, Oba, and Takagi (104) determined cadmium ion by the unorthodox procedure of electrolyzing the cadmium into a mercury pool and measuring the resistance of the resulting cadmium amalgam LITERATURE CITED
Achiwa, S., J . Electrochem. SOC.J a p a n 17, 18 (1949). Adams, K.N., ANAL.CHEM.26, 1933 (1954). Agasyan, P. K., Vestnik Moskov. rniz.. 8 , Ser. Fie-Mat. Estestren. Nauk, KO. 5 , 121 (1953). ;lichenegg, P., Haynes, H. G., J . A p p l . Chem. 4, 137 (1954). dmin, A. AI., Issa, I. A I . , Issa, R. M.. Chemist Analyst 43, 16 (1954).
.%ntsel, P., Chim. Chrorcika 20, 31 (1955). Baker, L. C. W.,AIcCutcheon, T. P., A s . 4 ~ .CHEX 27, 1625 (1955).
Bates, R. G., Ibid., 26, 871 (1954). Bates, R. G., “Electrometric pH Determinations,” Wiley, New York. 1954. Belcher, R., Gibbons, D., West, T. S.,ASAL. CHEM.26, 1025 (1954).
Belcher, R., Gibbons, D., West, T. S.,A n a l . Chim. Acta 12, 107 (1955).
Blaedel, W. J., Knight, H. T., ANAL.CHEM.26, 741 (1954). Bock, R., Hermann, 11..2. anorg. u . allgem. Chem. 273, 1 (1953).
Bottei, R. S.,Furman, ?i. H., XSAL.CHEM.27, 1182 (1955). Brauer, E., Staude, H., Z . wiss. Phot. 48, 16 (1953). Brockmann, H., Meyer, E., Chem. Ber. 86, 1514 (1953). Brunishols, G., A n a l . Chim. Acta 10, 470 (1954). Burriel, F., Conde, F. L., Jimeno, S.8., Ibid., 10,301 (1954). Capitani, C., Gambelli, G., Chimica e industria 35, 890 (1953). Capitani, D., Imperiale, P., Ibid., 36, 606 (1954). Carson, W. K., Jr., .INAL.CHEY.26, 1673 (1954). Carson, W. K.,Jr., Michelson, C. E., U. S. Atomic Energy Commission, Techniral Information Service, Oak Ridge, Tenn.. HW-26763 (1953). Cartm, W. N., Jr., Nichelson, E. C., Koyama, K., ANAL. CHEM.27,472 (1955). Chanin, M., Science 119, 323 (1954). Charlot, G., Chim. anal. 36, 63 (1954). Charlot, G., Compt. rend. reunion 1951, 227. Chilton, J. hl., Horton, A. D., ANAL.CHEM.27, 842 (1955). Codell, hI., Norwitz, G., RIikula, J. J., Ibid., 27, 1379 (1955). Cogbill, E. C., Kirkland, J. J., Ibid., 27, 1611 (1955). Coursier, J., A n a l . Chim. Acta 10, 182 (1954). Ibid., p. 265. Critchfield, F. E., Johnson, J. B., ANAL.CHEM.26,1803 (1954). Cundiff, R. H., hlarkunas, P. C., Ibid., 27, 1650 (1955). Cuta, F., Burianac, Z., Chem. Listy 49, 503 (1955). Day, H. O., Jr., Gill, 3. S.,Jones, E. V., Marshall, W. L., ANAL.CHEM.26, 611 (1954). Deal, V. Z., Wyld, G. E. a., Ibid., 27, 47 (1955). DeVries, J. E., Schiff, S.,Gants, E. S.C., Ibid., 27,1814 (1955). Diehl, H., Butler, J. P., Ibid., 27, 777 (1955). Dilts, R. V., Furman, N. H., Ibid., 27, 1275 (1955). Ibid., p. 1596. Dole, V. P., Thorn, N. A., Ibid., 27, 1184 (1955). Duyckaerts, G., IndustTie chim. beloe 18, 795 (1953). Eades, C. H., Jr., McKay, B. P., Romans, W. E., R u 5 n , G. P., ANAL.CHEM.27, 123 (1955). Elving, P. T., Ibid., 26, 1676 (1954). Erdey, L., Mazor, L., Acta Chim. Acad. Sci. Hung. 3, 469 (1953). Frisque, A,, Meloche, V. W., ANAL.CHEM.26, 468 (1954). Fritz, J. S., Ibid., 26, 1701 (1954). Fritz, J. S.,Fulda, M. O., Ibid., 25, 1837 (1953).
ANALYTICAL CHEMISTRY Fuji. S., Ishikawa, F.. J . Electrochem. SOC.J a p a n 18, 187 (1950). . 26, 84 (1954). Furman, K. H., h . 4 ~ CHEM. Gerhardt, G. E., Lawrence, H. C., Parsons, J. S., Ibid., 27, 1752 (1955). (52) Glenn, R. .1.,Olleman, E. D., Ibid., 26, 350 (1954). (53) Glenn, R. A . , Peake, J. T., Ibid., 27, 205 (1955). (54) Gordon. C. L.. Ibid.. 27. 1508 (1955). iSSl F.. ., Gremillinn. - .. ~ -4. ~ Ibid.. ~ , 27., 1.1R'f195.b ~ ~. ~ ~ . \ - -. -~ -,. (56) Grunwald,'E.. Ibid., 26, 1696 (1955). (57) Hahn, R. B., Kelley, RI. T., A n a l . Chim. Acta 10, 178 (1954). (58) Hall, C. E. X-., Stone, K. G., ANAL.CHEY.27, 1580 (1955). (59) . . Hallikainen, K. E., Pomueo, D. J., U. S. Patent 2,668,097 (Feb. 2, 1954). (60) Harwell, K. E., ANAL.CHEM.26, 616 (1954). (61) Heyn, A. H. .4.,Bergin, AI. J., J . Am. Cheni. SOC.75, 5120 (1953). (62) Hinsvark, 0.S . ,Stone, K. G., ANAL.CHEM.27, 371 (1955). (63) Hubbard, Donald, J . Research .VatZ. Bur. Standards, 50, 337 (1953). (64) Ikeda. N., Komookn, H., J . Chem. SOC.J a p a n 74, 473 (1953). (65) Ingraham, L. L.. hlakower, B., XSAL.CHEM.27, 916 (1955). Analust 78,487 (1953). (66) Issa, I. AI., &Lwad,S. .1.. (67) Issa. I. AI., Issa, R. AI., .4bdul, -1.d.,A n a l . Chim. Acta 10, 474 (1954). S A L . CHEW25, 1764 (1953). (69) Janz. G . J., Taniguchi, H., Chem. Rea. 53, 397 (1953). CHEM.27, 99 (1955). (70) Jones, H. B.. Baum, H., AICAI.. (71) Jordan, Joaeph. Ibid., 27, 1708 (1955). (72) Kahlweit, M.,Strehlow, H., Hocking, C. S., 2.p h y s i k . Chem. 4, 212 (1955). (73) Kamienski, B., Bylo, Z., Waligora, B., Bull. intern. acad. polon. sei.. Classe sci. math. nat., Ser. -4,1951, KO.3-6& 199 (1952). (74) Kamienaki, B., Puchalka, K., Dolinski, Z., Bull. acad. polon. sei. 1, 297 (1953). (75) Karchmer. J. H., Walker, 11.T., ASAL.CHEY.27,37 (1955). (76) Kauko, Y., Icel, 11.,2. anal. Chem. 142, 401 (1954). (77) Keller, 11. E., Iiunch, R. H., ASAL.CHEIM. 26, 1518 (1954). (78) Kieffer, F.. Rumpf, P., C o m p f . rend. 238, 700 (1954). (79) Kies, H. L., Anal. Chim.Acta 10, 161 (1954). (80) Kimoto, I
