Ramaswamy, D., BuU. Central Leather Inst., Madras (India) 3, 377 (1957). (95) .Nayudamma, Y., Ramaswamy, D., Zbzd. 4, 201 (1958). (96) Novikova, E. N., Petrova, L. N., Zhur. Anal. Khim. 12. 534 - - - (19.57). (97) Oiwa, I. T., -Sz. Repwts T8hoku Uniu., First Ser. 41, 47, 129 (1957). (98) Oiwa, T., Ando, K., Tanaka, Tanaka. N.. N., N i p p m Kagaku Zasshi 78,75 (1957). (99) Patchornik, A., Rogozinski, S. E., I
\ - - -
.
I
ANAL.CHEM.31.986 (19.59). (100) Paul, R. C.,’S%gh, G., Current Sci. 26, 391 (1957). (101) Paulsen, A., Medd. Norsk Farm. Selskap 18, ‘145 (1956). (102) Pearson, R. G., Vogelsong, D. C., J. Am. Chem. SOC. 1038 - 80. ~ - - (1958). (103) Pernarowski, M., Blackburn, D. W., J . Am. Pharm. Assoc. 47,585 (1958). (104) Pickard, P. L., Iddings, F. A., ANAL.CHEM.31 , 1228 (1959). (105) Pocker, Y., J . Chem. SOC. 1958, 240. (106) Pohloudek-Fabini, R., Konig, K. K., Phurm. Zentralhalle 98, 176 (1959). (107) Popov, A. I., Holm, R. D., J . Am. Chem.SOC.81. 3250 (1959). (108) Porter, G. B., ’Baughan, E. C., J. Chem. Soc. 1958, 744. (109) Ramas%-amy, D., Rajalakshmi, P. V., Nayudamm, A. Y., Bull. Catral \ - - - - ,
I
\ - - - - ,
Leather Research Inst., Madras (India)
5,255(1959). (110) Roberts, C. W., McBee, E. T., Hathaway, C. E., J . Org. Chem. 21, 1369 (19561.
Bull.
irai, H., Sahashi, Y., Takc Kenkyujo Nempa 8, 127 (1956;.
(115) Sakurai, H., Yoneda, Y., Komura, T., Yakugaku Zasshi 78, 1435 (1958)
Review
(116) Salomaa, P., Acta Chem. Scand. 1 1 , 125 (1957). (117) Salvesen, B., Medd. N w s k Farm. Selskap 19, 199 (1957). (118) Sarson, R. D., ANAL. CHEM.30, 932 (1958). (119) Satchell, D. P. K.,J . Chem. SOC. 1958,3910. (120) Schwabe, K.. Chem. Ina. Tech. ’ 31: 109 (1959). ’ (121) Schwibe, ’K., h’alurwissenschafta 44, 350 (1957). (122) Sensabaugh, A. J., Cundiff, R. H., hlarkunas. P. C.. ANAL. CHEM. 30. 1445 (19%). (123) Sheldon, J. C., Tyree, S. Y.,Jr., J . A m . Chem. SOC.81, 2290 (1959). (124) Shkodin, A. XI., IzmaUov, S. A,, Dzyuba, S . P., Uchenye Zapiski Khar’kov. Cnw. 71, 261 (1956). (125) Shkodin, A. hi., Karkuzaki, L. I., Dybskaya, Z. S., Ibid., 71,33 (1956). (126) Shkodin. A. >I.. Karkuzaki. L. . I.,, KhimenGo, M. T:, J . Gen. Ckem. U.S.S.R. 27, 31 (1957). (127) Shkodin, A. >I.) Karkuzaki, L. I., Khimenko, I f . T., Zhur. Obshchef Khim. 27, 29 (1957). (128) Sims, D., Peters, L., .Vature 180, 805 f1957). (129i Singh: J., Paul, R. C., Sandhu, S . S., J . Chem. SOC.1959, 815. (130) Skrynnikova, G. N . , hlatveeva, S . I., Ivshina, E. K., Trudy Vsesoyuz. Nauch.-Issledovalel. Inst. p o Pererabotke Slanlsev 1958. 227. (131) Spandau,H., Hattwig, H., 2. anorg. u. allgem. Chem. 295, 281 (1958). (132) Stenby, P. S., Ph.D. thesis, Eid-
genossische Technische Hochschule, Ziirich, 1957. (133) Stock, J. T., Purdy, W. C., Chemist Analyst 47, 37 (1958). (134) Stock, J. T., Purdy, W. C., Chem. Raw. 58, 1159 (1958). (135) Streuli, C. A., ANAL. CHEM. 30, 997 (1958).
(136) Streuli, C. A., Miron, R. R., Ibid., 30,997 (1958). (137) Susz, B. P., Chalandon, P., Helu. Chim. Acta. 41, 1332 (1958). (138) Susz, B. P., Lachavanne, -4., Ibid., 41, 634 (1958). (139) Taniguchi, H., Janz, G. J., J. Phys. Chem. 61 , 6% (1957). (140) Tsao, K., Loo, Y., Tang, T., l’ao Hsueh Hsueh Pao 4,281 (1956). (141) Turska, E., Wolfram, L., Zeszyty h’auk. Polztech. Lddi. KO.22. Chem. KO.7, 79 (1958). (142) Tutunzhich, P. S., Liler, M., Kosanovich, B., Glasnik Khem. Drushtva, Beograd 19, KO.9, 549 (1954). (143) Tutunzhich, P. S., Putanov, P., Ibid , 21, 33 (1956). (144) Ibid., p. 257. (145) Vaicum, Lydia, h a l e l e Univ. “C.I. Parhon” Bucurevti, Ser. Stiinf. nat. No. 10, 133 (1956). (146) Vaillant, II., Chim. anal. 39, 431 (1957). (147) van der Heijde, H. B., Bnal. Chim. Acta. 16. 392 (1957) (148) Ibid.; 17,512 (19i7) (149) van der Heiide. H. B., Dahmen, ‘ E.’A. hi. F., I W : , 16, 378 (1957). (150) van Meurs, N., Chem. Weekblad 54, 298 (1958). (151) Vincent, hf. C., Blake, hI. I., J . Am. Pharm. dssoc., Sci. Ed. 48, 359 (1959). (152) Wang, S. &I., Starr, H. W., Hoffman, R. J., Drug Standards 26, 116 (1958). (153) )Vimer< D. C.. ANAL. CHEM. 30, . 77; 453 (1958). ’ (1%) Yakubik, 31. G., Safranski, L. W., . Mitchell, J., Jr., Ibid., 30, 1741 (1958). (155) Yokoyama, F., Chatten, L. G., J . Am. Pharm. Assoc. 47, 548 (1958). (156) Zaugg, H. E., Garven, F. C., Ax.4~. CHEM.30, 1444 (1958).
of Fundamental Developments in Analysis
Amperometric Titrations ti. A.
laitinen
University o f Illinois, Urbana, 111.
S
INCE the
last review (66) (October 1, 1957, to October 1, 1959) the amperometric method has continued its steady rate of development. Emphasis has been placed on automation and scaling down to micro scale titrations. Relatively little work has been devoted t o the investigation of novel electrode systems; the brunt of the load has been carried by the time-honored rotating platinum and dropping mercury electrodes, designated as is customary by r.p.e. and d.m.e., respectively. In t h e present review, applied potentials are referred to the saturated calomel electrode (S.C.E.). According t o the tentative recommendation of the Commission on Electrochemical Data of the Analytical 180 R
0
ANALYTICAL CHEMISTRY
Chemistry Section of the IUPAC (22), the so-called “dead-stop” method is to be called a “bi-amperometric titration,” a term suggested by I. M. Kolthoff. I n this connection, Jlintti (41) proposed the name “diamperometric end point.” The theory of such titrations has been considered by Kao and Hsu (46) and Kies (54). Several reviews of the amperometric method have appeared (55, 86, 102, 109,I l l ) . Michalski (77) has reviewed the principles involved in titrations without the use of external applied e.m.f. APPARATUS AND METHODOLOGY
Several devices for carrying out
automatic amperometric titrations have been described. Juliard (44) titrated small amounts of chloride by means of a syringe buret and a detector for the minimum current in a titration involving a specially pretreated silver cathode and a mercury pool anode. The minimum detector consisted of a recorder with a microswitch set to operate when the recorder has just passed its minimum reading. An apparatus for automatically recording titration curves, in which a Selsyn servolinkage is used to synchronize a syringe buret and the chart drive, has been patented (88). Several automatic coulometric titraton with amperometric end point detection have been described. Cotlove, Tmntham, and Bowman (18) used anodically
generated silver ion for automatic chloride titrations; Barendrecht (6) used anodically generated iodine for a n automatic Karl Fischer titration of water; and Liberti (73) used cathodically generated ferrous iron for the automatic titration of dichromate, permanganate, and vanadate. Liberti (72) followed gas chromatographic separations of sulfhydryl compounds by automatic titration with electrolytically generated silver ion. A transistorized amplifier with a n amplification factor of 275 has been applied to the bi-amperometric Karl Fischer titration (88). A simple apparatus, using the r.p.e., a calomel electrode, and a resistor across which the potential drop is measured, ha3 been suggested (56). Efforts have been directed towards the titration of microgram quantites of zinc and copper (123), iodine (57, 95, 126), sulfhydryl (70), and ascorbic acid (43). An extreme example of scaling down is that of titrating on a microscope stage in volumes of the order of 10-3 ml. using a vibrating platinum electrode (911. Novel electrode designs include the rotating mercury pool electrode (RMPE) for niercurimetric sulfhydryl tirations (62), and the rotating aluminum (63) and palladium (35) electrodes for fluoride titrations. Reference electrodes of manganese dioxide and lead dioxide have been used for titrations a t positive potentials without external applied e.m.f. (39, 40). The square wave titration of Laitinen and Hall (68) has been found by Riolo and Soldi (103) to be as accurate as, and more rapid than, potentiometric or amperometric titrations for several redox and precipitation reactions. Amperometric titrations in fused salt media include the titration of iodide with silver nitrate or potassium dichromate (871, and the titration of chromium(I1) or vanadium(I1) R ith electrolytically generated iron(II1) (67). ION COMBINATION REACTIONS
Khadeev and Okolova (50),in studying the effect of dissolved oxygen on precipitation titrations involving lead (11), zinc(II), and copper(II), found a depressing effect of the diffusion currents of the metal ions due to the precip itation of hydroxides or basic salts in the alkaline region surrounding the d.m.e. a t rvhich oxygen reduction is going on. The disturbing effects were eliminated by titrating a t p H less than 2.5, or by using strongly buffered solutions. Silver halide titrations have been described in several publications. Cali, Loveland, and Partikian (15) determined traces of halogens in petroleum products by a procedure involving combustion followed by amperometric titra-
tion. Enoki and Morisaka (25, 26) studied the bi-amperometric titration of halides and cyanide using a pair of platinum or silver electrodes. They recommended the addition of hydrogen peroxide when using platinum electrodes, but found it unnecessary when using silver electrodes. Xjland and Eggels (85) titrated iodide and chloride successively in a single titration, and reported satisfactory results with quantities of chloride ranging from 0.25 to 20 times the amount of iodide. By using the proper applied potential, Bozsai (11) was able to titrate silver in the presence of large amounts of copper, in the analysis of silver bronzes. The automatic titration procedures (18, 4)have already been mentioned. I n the coulometric titration of cyanide, Przybylowicz and Rogers (97) found that the results with electrolytically generated mercury(I1) were slightly superior to those with silver(1) generated under the same conditions. Fluoride determinations have attracted considerable attention. Iron (111) has been used as a titrant with the r.p.e. (36, 83). Harris (35) found palladium to be superior to platinum as an electrode material in the titration of fluoride with thorium(1V) using iron(II1) as an amperometric indicator. Kolthoff and Sambucetti (63) devised a novel titration involving the use of a rotating aluminum electrode, which is anodically depolarized by fluoride ion, An amperometric titration with aluminum(II1) was found to be superior to one with thorium(1V) using this electrode. Dumontier-Goureau and Tremillon (24) also observed the anodic depolarization effect of fluoride on an aluminum electrode and suggested its possible application to an amperometric titration. McEwen and De Vries (75) used the anodic oxidation wave of uranium(1V) to give uraniuni(V1) a t the d.m.e. to indicate the end point of a titration of fluoride with uranium(1V) nitrate or perchlorate. The method yielded variable results, the F-/U ratio varying between 1.8 and 2.1 in formate or monochloroacetate buffers of pH 3.5 to 3.7. Ferrocyanide precipitation methods for several metals have been studied. Enoki and coworkers (28), using a miuture of ferri- and ferrocyanides in biamperometric titrations, found that in metal ion precipitations in general, the ferrocyanide was less soluble ttian the ferricyanide, and that the end point corresponded to the ferrocyanide stoichiometry. Michalski and Galus (7’9) titrated relatively largt amounts of calcium or magnesium in alcohol-water mixtures with ferrocyanide, using either a single platinum indicator electrode or two indicator electrodes. Basinski and Kuik (7) titrated cadmium(I1) with LLFe(CN)6 in a supporting electrolyte
of LizSoI to form Cd2Fe(CN)6. The method is of limited applicability because potassium and ammoni.um ions must be absent. In the presence of potassium or ammonium salts, Ramaiah and Agarwal (100, 101) found the stoichiometry to correspond to a precipitate composition K&ds [Fe(CX)6]+ Kao and Chuang (45) found the composition (NH4)&d5[Fe(CN)6I4for the cadmium precipitate, whereas zinc gave (NH4)2Zn3[Fe(CN)6]2 from 1-11 hydrochloric acid containing ammonium sulfate. Similarly, Saraswat (205) reported the composition &COS[Fe(Cx)6]4 upon titration of cobalt(I1) with K F e (CN), in 1Mpotassium chloride medium. The anodic wave of ferrocyanide ‘at a platinum electrode has been used as the basis for the titration of small amounts of zinc in the presence of large amounts of iron, aluminum, alkaline earths, and alkali metals (123). I n a citrate medium in the presence of vanadate and iron(II1) interference of iron(I1) could be avoided by oxidizing it with dichromate. The resulting chromium(II1) did not interfere ( I 07). Ferrocyanide was titrated with chromium(II1) urea solution, measuring the diffusion current of the first reduction wave of chromium (111) (34). Bismuth has been determined in the presence of a number of other metals by precipitation as the aminopyrine salt of HBi14 in 2.5M sulfuric acid (130), and by titration of its basic iodide by silver nitrat,e (80). Two indirect procedures for sulfate have appeared. I n the first, barium sulfate is precipitated in an ammonium acetate buffer of pH 5.5 to 6.2 with a slight excess of barium, which is backtitrated with potassium chromate (216). I n the other procedure, sulfate is precipitated by means of a n acid solution of barium chromate, the excess chromate being determined by an iodometric bi. amperometric method (125). The titration of barium ion with lithium sulfate (131) in an ethanolwater solution of tetraethylammonium bromide a t a n applied potential of -2.0 volts appears to be of limited applicability because of the interference of many reducible materials. Oxalate has been applied as a precFpitant by Usatenko and Vitkina (119, 120). Lead was titrated using copper(I1) as an amperometric indicator (120) with the r.p.e., and mercury, silver, calcium, and iron(II1) were titrated a t p H 3.6 to 4.7, observing the diffusion current a t -0.9 to 1.0 volt (119) with the r.p.e. or d.m.e. Because oxalate is reducible a t this potential, V-shaped titration curves are observed except in the case of calcium. Copper and zinc were determined in b r a s and bronze alloys, using the r.p.e. (61, 6.2). Copper(I1) was reduced with ascorbic acid and titrated with thiocyVOL. 32, NO. 5, APRIL 1960
181 R
anate. Good results were obtained except in the presence of chloride, which caused low results probably because of the coprecipitation of cuprous bhloride with the thiocyanate. Zinc was determined by titration with K2Hg(SCN)( to form ZnHg(SCK),. Both metals could be determined in 12 to 15 minutes. A titration of cadmium ion in sulfate solution, in the presence of pyramidone, with (NH4)2Hg(SCN)4 to give a Vshaped curve with the d.m.e. has been reported (93). A direct amperometric titration of potassium with sodium tetraphenylborate \vas described by Amos and Sympson (1). The current due to anodic depolarization of the d.m.e. a t a n applied potential of +0.08 volt (us. S.C.E.) n a s observed. Chloride interfered only a t concentrations of 0.32M or higher. The more usual indirect method, involving the titration of the tetraphenylborate of potassium or of organic bases with silver nitrate, has also been studied (37). A report on the application of the iron(II1) titration of orthophosphate to the analysis of superphosphate ( 2 ) has indicated results low by 1.5y0as compared to the chemical method. The low results were attributed to the coprecipitation of secondary phosphates of calcium and magnesium. I n the titration of cobalt(I1) with sodium triphosphate a t p H 7 , the composition of the product has been demonstrated O - ~confirmed , by isolato be C O P ~ O ~ and tion of the trisodium salt (58). The titration of lead in 0.1 to 1.ON nitric acid with sodium diethgldithiophosphate to precipitate the lead salt has been followed with the r.p.e. (13). Heavy metals of the hydrogen sulfide group interfered. The complex formation reaction between uranium(VI), aluminum(II1) , and citrate was studied (9) by an amperometric titration of a solution of uranium (VI) in citrate solution with aluminum (111), observing the reduction current of uranium(V1) a t -0.53 volt, using the d.m.e. A mole ratio of 1 to 1 of uranium to aluminum in the citrate complex was indicated. Several applications of EDTA have appeared, in which the diffusion current of the uncomplexed metal ion has been measured. These include the titration of copper and lead in a n acetate buffer of p H 4.2 (114), indium a t p H 1 (122) using the d.m.e., and iron(II1) in nitric acid of concentration below 0.1M or in a n acetate buffer, using the r.p.e. shortcircuited to the S.C.E. (129). The same electrode system has .been used for the titration of mercury(I1) in nitric acid solution, adjusted to p H 7.5 and buffered with acetate, for the purpose of determining mercury in organic compounds (110). The anodic oxidation current of EDTA a t a platinum elec182 R
ANALYTICAL CHEMISTRY
trode has been used for the titration of zinc a t p H 3 to 4.5, cobalt(I1) in weakly acid solution, and bismuth a t p H 1 to 2 (118). The applied potential was adjusted between 0.55 and 0.9 volt, depending upon the medium. A displacement reaction was used by Flaschka and Barakat (29)for the titration of thorium. A solution of thoriurn(1T') was treated with lead-EDTA complex. The displaced lead ion was titrated nith EDTA, using a d.m.e. with an applied potential of -0.7 volt. Martin and Reilley (76) used a single polarized mercury indicator electrode, or a bi-amperometric system of two mercury electrodes to titrate calcium or copper(I1) with EDTA. The electroactive species is the mercury(I1)-EDTA complex. Other metal ions and chelates could be used with similar electrode systems. OXIDATION-REDUCTION REACTIONS
Methods Based on Iron. The titration of dichromate with iron(I1) using the r.p.e. has been applied t o t h e dctermination of antimony, by oxidation of antimony(II1) mith excms dichromate and back-titration of the eacess 120). Arsmic interferes. The method of Butenko and Bekleshova ( 1 4 , in n-hich chromium. vanadium, and manganese are determined by peroxydisulfate oxidation followed by iron(I1) titration, has been successfully applied to titanium alloys (3). An acidity of 10 volume yo sulfuric acid was necessary to avoid the hydrolysis of titaniuni(1V). The bi-amperometric titration of cerium(1V) with iron(I1) has been studied for verification of the theoretical interpretation of the method (47). Minor discrepancies were observed. Iron(II1) has been used as an oxidant for molybdenum(II1) in sodium chloride-hydrochloric acid qedium (16). An indirect method for phosphorus was based on the reduction of the molybdenum(V1) in molybdiphosphate to molybdenum(II1) by means of zinc amalgam, followed by oxidation t o molybdenum(V) using iron(II1). The titration of iron(II1) with ascorbic acid has been compared with the EDTA titration (129). The ascorbic acid method is not influenced as much by acidity, or by nonoxidizing foreign ions, On the other hand, it is less sensitive, less precise, and slower than the amperometric E D T A method, and the reagent is less stable. The bi-amperometric titration of ferricyanide in alkaline solution with arsenic(II1) using oso4 as a catalyst has been reported (108). The back-titration of excess ferricyanide in the presence of the oxidation products of various reducing agents was also described. Methods Based on Halogens. T h e titration of microgram amounts of iodine (57, 96, 126) with thiosulfate has
been applied primarily to the Winkler method for dissolved oxygen in amounts of the order of 0.001 p.p.m. Ascorbic acid has been used for the titration of iodine, and for several indirect iodometric determinations (32). Sulfide, in amounts of 10 to 30 y, and collected as cadmium sulfide, has been successfully titrated by the biamperometric method (69), using standard iodate as the titrant to produce iodine. The standard deviation of replicates was 1.4 y. The coulometric generation of iodine for the Karl Fischer determination of water has been mentioned above, as an example of an automatic titration (6). Coulometrically generated halogen has also been used by Hibbs and Wilkins (38) for the oxidation of sulfur dioxide to sulfate, using the bi-aniperometric end point. They described two methods. I n the first, a solution of bromide containing a small quantity of iodide i s elect'rolyzed. The authors consider that iodine is formed by reaction of electrolytically generated bromine with iodide. It appears likely, however, that iodine bromide is formed as an intermediate. I n the second method, the sulfur dioxide is oxidized by an excess of ferricyanide, and the resulting ferrocyanide is then reoxidized by coulometrically generated bromine, Both methods were applied to the deternlination of sulfur in siliconiron. Iodate has been used as an oxidant for thiourea, hydrazine, thiosulfate, and thiocyanate by adding an excess of this reagent in 1 to 2N hydrochloric acid containing mercury(I1) chloride (4). Using a bi-amperometric end point the excess iodate was back-titrated with standard arsenic(II1). I n a comparison of colorimet.ric and amperometric determinations of arsenic (111), Kassian and Riedel(48) concluded t,hat the colorimehric method gare accurate results Ivith amounts of arsenic as low as 5 y, whereas the amperometric m t h o d became inaccurate with amounts below 30 y. This conclusion is a t variance, however, r i t h the previous results of other investigators (55) who were able to titrate 7 y of arsenic with good accuracy. Tin(I1) has been titrated with bromate in 1N hydrochloric acid containing 0.05N potassium bromide. Careful exclusion of air is necessary to prevent air oxidation (112). Selenite has been titrated to selenate in a bicarbonate medium, using sodium hypobromite as the tit.rant and a potential of +0.3 with the r.p.e. (2s). Bromide has been used as a reducing titrant for permanganate (63) in a mixed sulfuric acid-phosphoric acid solution. The product,s were manganese(I1) and bromine. Other Redox Titrations. Chromium(I1) has been used as a titrant,
for reducing molybdenum(V1) t o (V) (30, 90). Chromium(I1) gives an anodic wave a t the r.p.e., beginning at 0.25 to 0.3 volt. Since neither molybdenum(V) nor (VI) undergoes electrode reactions at 0.35 volt, titration to zero current permits the titration of permanganate in the presence of molybdate (30) and the anodic current of chromium(I1) marks the end point of the molybdate reaction. Similarly, dichromate can be titrated a t zero potential, and the sum of dichromate and molybdate can be determined a t 0.35 volt. Ascorbic acid has been used as a reducing agent for cerium(IV), vanadium(V) ( S I ) , and iridium(1V) ( 9 8 ) . Iridium(1V) has also been titrated with hydroquinone, using for either reagent the r.p.e. a t a n applied potential of 0.4 to 0.5 volt a t p H 1.5. Electrolytically generated vanadyl ion has been used for the titration of permanganate in 0.5M sulfuric acid (21). Silver(I1) was used to oxidize manganese(I1) to permanganate. Because vanadium(1V) is a weak reductant,, few oxidants [notably chromium (VI) ] interfere Conversely, vanadium (V) has been used as a weak oxidant, for the titration of uranium(1V) to (VI) (81). Arsenic(II1) has been used for the selective reduction of H2S05 in the absence of catalyst, H20, a t room temperature in the presence of osmium tetroxide and molybdate as a mixed catalyst, and H&08 a t 60' to 70" with the same catalysts but a t a higher acidity (20). I n each case, a biamperometric titration was carried out, either with two platinum electrodes or with a platinum-carbon electrode pair. The Volhard method for titration of manganese(I1) to manganese(1V) oxide with permanganate has been studied amperometrically, using a platinumsilver electrode pair (33). The titration to manganese(II1) in pyrophosphate medium was found to give results accurate to 0.1% in the absence of foreign ions, and using a pyrophosphate concentration of a t least 0.2iM. The effect of foreign ions is less pronounced than in the Volhard method (33). Using the anodic current of lead(I1) as the indicator current, Khadeev and Kikurashina (49) were able to follow the titration of lead(1I) with permanganate in weakly alkaline solution using zinc oxide and mercuric oxide as catalysts. The titration of lead(I1) in an acetate buffer with dichromate to give lead chromate was found t o be less subject to interference. The method x a s applied to the analysis of lead bronze. TITRATIONS INVOLVING ORGANIC REAGENTS
The literature of organic reagents in
amperometric titrations has been reviewed by Pope1 (93). Methods involving the tetraphenylborate ion have been included above under ion combination reactions. hlusina and Songina (84) have described the voltammetric properties of several organic reagents, including abenzoinoxime, 1-nitroso-2-naphthol, 8quinolinol, and pyrogallol. I n each case a wave suitable for amperometric titrations, a t either the d.m e. or r.p.e., was observed. Anthranilic acid and benzidine gave no suitable waves a t either electrode. Sodium anthranilate has been used as a direct titrant for copper and lead in acetate media a t p H 3 to 7, and zinc in sodium nitrate a t p H 4.2 to 5.5 (65). I n each case, the reduction wave of the metal ion was observed. Diantipyrinyhethane p r e c i p i t a t es bismuth and cadmium from solutions containing their bromide complexes (94). The method appears to be especially interesting for cadmium, which can be titrated in the presence of relatively large amounts of other metal ions, using the d.m.e. at an applied potential of -0.8 volt. Sodium diethyl dithiocarbamate gives an anodic diffusion current a t 0.7 to 0.9 volt that is useful for amperometric indication (117 ) . The method has been applied to the determination of copper in babbitt and other alloys. Cupferron has been used as a precipitant for tin(IV), using the d.m.e. at -0.8 volt in 3M ammonium sulfate2.1.1 sulfuric acid (127). A distillation as the tetrabromide, followed by ammonia precipitation using aluminum hydroxide as the carrier, served as a method of separation. Antimony could be removed by a prior distillation as the chloride. Tannin has been used for the direct titration of tin(1V) Gsing the d.m.e. a t -0.6 volt in 4M ammonium chloride0.05X hydrochloric acid as the supporting electrolyte (113). a-Furildioxime has served as a titrant for palladium in concentrations of to l O - 4 M , using the r p.e. Several other reagents, including @-furfuralOYime, dimethylglyoxime, and 8-quinolinol were also found to be suitable ( 5 ) . p-Xitrophenylazoresorcinol has been suggested as a possible titrant for magnesium, using the d.m.e. ( 6 4 ) . Two indirect methods for magnesium, involving the titration of precipitated magnesium 8-quinolinolate have been devised by Powers, Day, and Underwood (96). I n the first, the oxinate. dissolved in an acetate buffer, is treated with potassium iodide and titrated with standard copper(I1) nitrate to form the copper oxinate. The iodine liberated after the end point is detected by the bi-amperometric method. I n the second method,'no
iodide is added, and the first excess of copper(I1) ion is detected with the d.m.e. a t an applied potential Qf -0.2 volt. An indirrct aluminum method using 8-quinolinol has been described (8). Instead of dissolving the precipitated oxinate, the excess reagent in an aliquot part of the filtrate is titrated in hydrochloric acid-potassium bromide medium with bromate.
DETERMINATION OF ORGANIC COMPOUNDS
The adaptation of the argentimetric sulfhydryl titration to micro scale pnd automatic operations (70-72) has been described. In a study of the effect of p H on the argentimetric and mercurimetric methods, Burton (1.2)found that the optimum p H depended t o some extent on the buffer and titrant system which was used. Kolthoff and coworkers (GO), in a study of the denaturation of proteins, found that Ihe mercurimetric method gave a better defined end point than the silver titration, using the r.p.e. The method was applied to the determination of sulfhydryl in native and denatured bovine serum ( 6 9 ) . A similar study (62) and application (61) were made of the rotated mercury pool electrode (RMPE) for the mercurimetric titration of sulfhydryl a t p H 2. Sluyterman (106) found high results in the argentimetric titration of sulfhydryl in cysteine hydrochloride, cysteine ethyl ester hydrochloride, and thioglycolic acid but nearly theoretical results for glutathione. He suggested that the proximity of the -NHz or -COOH groups to the sulfhydryl was responsible for the high results. An oxidimetric titration of cysteine with ferricyanide a t p H 7 , using the biamperometric method, has been reported to give results precise to within 1% wi'h amounts as small as 1 pniole (124). The bromination of phenols by coulometrically generated bromine has been studied by Lichtenstein (74) and by Ciita and KuEera (19). I n the latter work, using 0.1M hydrobromic acid the stoichiometric mole ratio of bromine to pheno! or o- or p-cresol was 1 to 1. For o-cresol a t p H 7 , and for pyrocatechol and resorcinol a t pH 11 to 12, the mole ratio was 3 to 1, while for the latter two compounds a t p H 4 to 5 it was 5 to 1. Ascorbic acid has been determined by coulometrically generated iodine, with a bi-amperometric end point (43). Submicrogram quantities could be determined. A conventional r.p.e. titration using bromate in hydrocbloric acidpotassium bromide has also been described (104). To determine glucose, van Pinxteren (92) added ferricyanide in alkaline VOL. 32, NO. 5, APRIL 1960
183 R
medium. After acidification, the resulting ferrocyanide was titrated with zinc sulfate, using the bi-amperometric method. The method is suitable for blood analysis. The direct titration of oxalic acid with cerium(1V) on 0.1M perchloric acid, a t 60” was followed by means of a platinum indicator electrode by Michalski and Czarnecki (78). Back-titration with oxalic acid was used for tartaric and citric acids, Thiourea was determined by adding excess iodate in 1 t o 2M hydrochloric acid containing mercury(II), and backtitrating with arsenic(II1) using the biamperometric method. Vitamin B l z A can be titrated directly with a solution of oxygen, using the d.m.e. as an indicator electrode, to give a dimeric product involving one molecule of oxygen (@). Silicotungstic acid has been used as a titrant for xanthine bases in 1.5N hydrochloric acid, at -0.80 volt with the d.m.e. (128). The same reagent has been used for methylene blue or methyl violet (89). Aldehydes and ketones can be titrated in 50% alcoholic sulfuric acid solution with 2,4-dinitrophenylhydrazine, using the d.m.e. as the indicator electrode (13.2, 133). The determination of sulfanilamide derivatives by use of a bi-amperometric indication of the ehd point of a diazo titration has been described by Enoki and Morisaka (27). Styrene has been titrated in glacial acetic acid, in the presence of 0.lM lithium chloride with tert-butyl hypochlorite (121). A bi-amperometric detection of the first excess of chlorine was used. I n the absence of chloride, the reagent itself gave no amperometric response. Tanaka and Tamamushi (116) showed that dodecylpyridinium chloride, when titrated with sodium dodecyl sulfate using the d.m.e. as the indicator electrode at -1.325 volts, shows a sharp amperometric end point. This titration appears t o be of interest in the determination of detergents, especially if a titrant containing easily reduced substituent groups to permit the use of a smaller applied potential could he used. Coetaee and KolthofT (1‘7) carried out acid-base titrations of tribenzylamine and urea with perchloric acid, using acetonitrile as the solvent. Either the aiiodic depolarization wave of the d.m.e. due to the formation of a stable mercury complex of the amine or the cathodic wave of the solvated proton could be used in the case of tribenzylamine. Urea does not give an anodic depolarization wave, but it can be titrated by measuring the solvated hydrogen ion wave in the presence of the wave due t o the protonated urea. 184 R
ANALYTICAL CHEMISTRY
LITERATURE CITED
(1) Amos, W. R., Sympson, R. F., ANAL. CHEM.31,133 (1959). (2) Analytical Research Group, Dept.
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Hua Hstieh Shih Chieh 13,451 (1958). (3) Aref’eva, T. V., Pats, R. G., Analiz Rud Tsvetnykh Metal. i Produktov ikh Pererabotki, Sbornik Nauch. Trudov 1958, No. 14, 74. (4) Bapat, M. G., Sharrna, B., 2. anal. Chem. !57, 258 (1957). (5) Bardm, M. B., Lyalikov, L. S., Zhur. Anal. Khim. 12, 390 (1957). (6) Barendrecht, E., Nature 183, 1181 (1959). (7) Basinski. A.. Kuik. M.. Roczniki Chem. 31,669 (1957j. ‘ ’ (8) Berrae, G., Rev. fac. ing. qutm. 26, 65 (1957). (9) Booman, G. L., Holbrook, W. B., ANAL.CHIEM. 31,lO (1959). (10) Boesai, I., Magyar Kem. Folyoirat 61,305 (1955). (11) ‘Zbid.,’62,386 (1956). (12) Burton, H., Biochim. et Biophys. Acta 29, 193 (1958). (13) Busev, A. I., Ivanyutin, M. I., Zhur. Anal. Khim. 13, 647 (1958). 114) Butmko. G. A.. Bekleshova. G. E.. ‘ Zavodskaya’Lab. 16, 650 (1950).’ (15) Cali, L. J., Loveland, J. W., Partikian, D. G., ANAL.CHEM.30,74 (1958). (16) Chlebovsky, T., Hutnick6 listy 3, 252 (1958). (17) Coetzee, J. F., Kolthoff, I. M., J . A m . Chem. SOC.79,6110 (1957). (181 .~ Cotlove. E.. Trantham. H. V.. Bowman, R. L.,’J. Lab. and Clin. Med: 51, 461 (1958). (19) Cilta, F., KuEera, Z., Chem. listy 52, 595 (1958). (20) Cz&nyi, L. J., SOlpOSi, F., Acta Chim. Acad. Sci. Huna. 17. 69 (1958). (21) Davis, D. G., ANAL.C & ~ . ’ 3 1 ,1460 (1959). (22) Delahay, P., Charlot, G., Laitinen, H. A., “A Nomenclature and Classification of Electroanalytical Methods,”
tentative report presented to Commission on Electrochemical Data at Munich IUPAC Conference, 1959. (23) Deshmukh, G. S., Bapat M G., Balkrishnan, E., Eshwar, M. b., Natur-
wissenschuften 45, 129 (1958). (24) Dumontier-Goureau, N., Tremillon, B., Bull. S O C . chim. France 1959, 132. (25) Enoki, T., Morisaka, K., Yakugaku Zasshi 77,841 (1957). (26) Zbid., p. 1240. (27) Zbid., 78, 432 (1958). (28) Enoki, T., Morisaka, K., Harada, T., Kakutani, N., I b X , 79, 679 (1959). (29) Flaschka, H., Barakat, M. F., 2. anal. Chem. 156, 169, 321 (1957). (30) Gallal, Z. A., Nauch. Doklady Vysshei Shkoly, Khim. i Khzm. Tekhnol. 1958, KO.3, 498. (31) Gallai, 2. A., Tiptsova, V. G., Peshkova, V. M., J . Anal. Chem. U.S.S.R. 12, 487 (1957). (32) Gallal, Z. A., Tiptsova, V. G., Peshkova, V. M., Vestnik Moskov Univ., Ser. Mat., Mekh., Astron., Fiz., Khim. 13, No. 1, 209 (1958). (33) Grubitsch, H., Nilsen, B. R., Z. anal. Chem. 163, 353 (1958). (34) Hagiwara, Z., Bunseki Kagaku 6 , 103 (1957). (35) Harris, W. E., ANAL. CHEM. 30, 1000 (1958). (36) Herder, J. J. den, Pinxteren, J. A. C. van, Pharm. Weekblad 93, 1013 (1958). (37) Heyrovsk?, A,, Chem. listy 52, 40 (1958). (38) Hibbs, L. E., Wilkins, D. H., Anal. Chim. Acta 20,344 (1959). (39) Ishibashi, M., Fujinaga, T., Saito, C., Nippon Kagaku Zasshi 79, 12 (1958).
(40)-Ibid.,p. 14. (41) Jiintti, O., Suomen Kemistilehti 28.4, 65 (1955). (42) Jaselskis, B., Diehl, H., J. Am. Chem. SOC.80,2147 (1958). (43) Jedrzelewski, W., Chem. Anal. 2, 453 (1957).
(1957). (49) Khadeev, V. A., Nikurashina, A. G., Uzbek. Khim. Zhur., Akad. Nauk Uzbek. S.S.R. 1958, KO.2, 11. (50) Khadeev, V. A., Okolova, Y. I., Trudy Sredneaziat. Goswlarst. Univ. im. V . Z. Lenina, Khim. 84, No. 10, 23 (1958). (51) Khadeev, V. A., Zhdanov, A. K., Uzbek. Khim. Zhur., Akad. Nauk Uzbek. S.S.R. 1958, No. 3, 57. (52) Khadeev, V. A., Zhdanov, A. K., Zauodskaya Lab. 23, 1290 (1957). (53) Khlopin, N. Y . , Gein, L. B., J. Anal. Chem. U.S.S.R. 12,584 (1957). (54) Kies, H. L., Anal. Chim. Acta 1 1 , 382 (19541.
’
. 62, 30 (1958). (58) Kobayashi, M., Nippon Zasshi 78.611 (19.57).
Kagaku
Ibid.. 79.5102 (1957). (61) Kblthoff, I.’ M., ’Anastasi, A., Tan, B. H., Zbid., 80, 3235 (1958). (62) Zbid., 81, 2047 (1959). (63) Kolthoff, I. M., Sambucetti, C. J., Zbid.. 81. 1516 (1959): Anal. Chim. Acta’21, 233 (1959). (64) Kostromin, A. I., Uchenye Zapiski Kazan. Univ. 115, No. 3, 65 (1955). (65) Zbid., KO. 1, Obshcheuniv. Sbornik 179 (1956). (66) Laitinen, H. A,, ANAL.CHEM.30, 657 (1958). (67) Laitinen. H. A.. Bhatia. B. B.. Zbid.. ’ 30, 1995 (1958). ’ (68) Laitinen, H. A., Hall, L. C., Zbid., 29,1390,1893 (1957). (69) Levin, L., Swann, W. B., Talanta 1,276 (1958). 170) Levine. S.. Instr. and Automation ‘ 30,883 (1957j . (71) Liberti, A., Anal. Chim. Acta 17, 247 (1957). (72) Liberti, A., Ricerca sci. 27, Suppl. A , Polarographia 3, 21 (1957). (73) Liberti, A., Ciavatta, L., Met. ital. 2, 50 (1958). (74) Lichtenstein, H. J., J. prakt. Chem. 6 , 225 (1958). (75) McEwen, D. J., De Vries, T., ANAL. CHEM.31,1347 (1959). (76) Martin, -4. E., Reilley, C. N., Ibid., 31,992 (1959). (77) Michalski, E., Chem. Anal. (Warsaw) 3, 423 (1958). (78) Michalski, E., Czarnecki, K., Zbid., 4 , s (19591.. (79) Michalslu, E., Galus, Z., Zbid., 3, 431 (1958). (80) Michalski, E., Ruskul, W., Zbid., 2, 284 (1957). (81) Morachevskii, Y. V., Tserkovnitskaya, I. A., Zhur. Anal. Khim. 13, 337 (1958). I
,
(82) Murayama, M., U. S. Patent 2,834,654(Ma 13,1958): (83)Musha, Higashmo, T., Nippon Kagaku Zasshi 77, 128 (1956). (84) Musina, T. K., Songma, D. A., Uchenye Zapiski Alma-Atinsk. Gosudarst. Pedagog. Inst. 6 , 125 (1955). (85) Nijland, M. M., Eggels, P. J. H., Chem. Weekblad 54,289(1958). ( 8 6 ) Nikolit, K., Archiv farm. 5, 217 (1955). (87) Novik, R. M., Lyalikov, Y. S., Zhur. Anal. Khim. 13.691 (1958). (88) Oehme, F., Chem. Tech. (Berlin) 9, 340 (1957). (89) Ogawa, T., Denki Kagaku 25, 613 (1957). (90)Peshkova, V. M., GallaI, Z. A.. . Alekseeva, ‘N. N., ’ Khim. ’ Redkikh Elementm, Akad. Nauk S.S.S.R., Inst. Obshchei i Neorg. Khim. 1957, No. 3, 119. (91) Petrikova, M. N.,Alimarin, I. P., Zhur. Anal. Khim. 12,462 (1957). (92)Pinxteren, J. A. C. van, Phamz. Weekblad 93, 753 (1958). (93) Popel, A. A., Uchenye Zapiski Kazan. Gosudarst. Univ. im. V . I . Ul’yanuvaLenina, Khim. 115,No. 3,69 (1955). (94)Zbid., cf. Chem. Abstracts 53, 17568 (1957). (95) Po’tter, E. C., White, J. F., J. Appl. Chem. 1957,309,317. (96) Powers. R. M.. Dav. R. A.. Jr.. ’ Underwood, A. L’, A ~ A L CHEM. . 30; 254 (1958). (97)Przybylowicz, E. P., Rogers, L. B., Zbid., 30,65 (1958). (98) . Pshenitsvn. N. K.. Ezerskava. N. A,. Zhur. Anal.“Khim. 14,81 (19g9): (99) Purdy, W. C., Burns, E. A., Rogers, L. B., ANAL.CHEM.27,1988(1955).
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“Trace Analvsis.” SvmDosium Trace Anal. N. Y. kcah. MLd.; 1955, p. 317, 1957. (103)Riolo, C. B., Soldi, T., Ann. chim. (Rome) 49.382 (1959). (104) Sant, B. R., Sfukherji, A. K., Current Sci. (India) 28, 16 (1959). (105) Saraswat, H. C., J. Sci. Znd. Research (India) 17B,45 (1958). (106) Sluyterman, L. A. E., Biochem. et Biophys. Acta 25, 402 (1957). (107) Solntsev, N. I., Chudina, R. I., Analiz Rwl Tsvelnukh Metal. i Produkt a , ikh Pererabotk, Sbmnik Nauch. Trudov 1958,No. 14,103. (108) Solvmosi. F.. Acta Chim. Acad. ‘ Sei. Hcng. 16, 267 (1958). (109) Songina, 0. A., “Amperometric (Polarometric) Titration in the Analysis of Mineral Raw Material” Moscow, Gosudarst. Nauch.-Tekh. izdatel. Lit PO Geol. i Okhrane Nedr., 1957. (llO).Southworth, B. C., Hodecker, J. H., Fleischer, K. D., ANAL.CHEM.30, 1152 (1958). (111) Stock, J. T., Microchem. J . 2, 229 I
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(116) Ten’kovtsev, V. V., Zhur. Akad. Khim. 12,504(1957). (117) Usatenko. Y. I.. TulvuDa. F. hf.. ‘ Zzvest. Vysshykh C‘cheh. Za;edeniZ, Khim: i Khim. Tekhnol. 1958,No.3, 56. (118) Usatenko, Y. I., Vitkina, Ll. .4., JVauch. Dokladv Vusshei Shkolv Khini. i Khim. Tekhnol: 1958. No. 3. 562 (119)Usatenko, Y. I.’, Vitkina, 31 1 Ukrain. Khim. Zhur. 23, 788 (195; (120)Usatenko, Y. I., Vitkina, AI. A., Zavodskaya Lab. 23, 427 (1957). (121) Van Hall, C. E.. Stone, K. G. ANAL.CHEM.30,1416 (1958).’ (122) Vladimirova, V. M., Zaoodskaya Lab. 23, 1286 (1957). (123) Voiloshnikova, A. P., KozlovskiI, M. T., Songina, 0. A., Ibid., 23, 273 (1957). (124) Wadill, H. G.,Gorin, G., ANAL. CHEM.30,1069 (1958). (125) Weiner, R., Key, E., Metalloberfluehe 11,377(1957). (126)Yamagishi, R., Konishi, Y., Asahi Garasu Kenkyu Hokoku 8, 47 (1958). (127) Yamamura, S. S., Re&, J. E., Booman, G. L., li. S. Atomc Energy Comm. IDO-14436(1958). (128) Yoshino, T., Yakugaku Zasshi 78, 1303 (1958). (129) Zhdanov, A. K., Khadeev, V. A., Kats, A. L., Uzbek. Khim. Zhur., Akad. Nauk Uzbek. S.S.R. 1958,No. 1,27. (130) Zhdanov, A. K., Khadeev, V. A., Khalilova, V. K., Zhur. Anal. Khim. 12,695 (1957). (131) Zittel, H. E., Miller, F. J., Thomason, P. F., ANAL. CHEM.31, 1351 (1959). (132) Zobov, E. V., Lyalikov, Y. S., Zzvest. Akad. Nauk Turkmen. S.S.R. 1958, No. 1, 93. (133) Zobov, E. V., Lyalikov, Y. S., Zhur. Anal. Khim. 11, 459.
Review of Fundamental DeveloDments in Analvsis
Potentiometric Titrations Charles N . Reilley University o f Norfh Carolina, Chapel Hill, N .
T
paper summarizes the chief trends in the development and application of potentiometric titrations since the prior review in this series HIS
(122).
The field of acid-base titrations in nonaqueous solvents has been reviewed by Riddick (I%!?), Kolthoff and Bruckenstein (83), and Van Poucke (155) (48 references). Kolling (86) has reviewed the nonaqueous methods proposed for volumetric analysis of inorganic compounds. Several aspects of potentiometric titrations in alloy analysis have been reviewed by MeLaren (96),especially for systems which do not lend themselves t o color change indicator methods. THEORETICAL DEVELOPMENTS
Membrane Electrodes.
Gregor
C.
and Schonhorn (59) have described the preparation and properties of a membrane electrode reversible to barium, calcium, and iron(III), which promises t o be of use analytically. To prepare such a n electrode, multilayers (50 monolayers thick) of the alkaline earth salts of stearic, hexadecyl- and octadecylsulfuric, and hexadecylorthophosphoric acids were deposited on the two “perfect fit” edges of a previously cracked glass slide. The edges could then be rejoined, with the multilayer film now bridging glass to glass (approximately 2500 A.), This “crack” constitutes the membrane electrode and allows alkaline earth cations to diffuse through the crack (multilayer membrane) in a direction normal t o the axis of orientation of the long-chain acids. When solutions containing different concentrations of barium, calcium, or
iron(II1) are placed on either side of the crack, and S.C.E. electrodes dipped into the solutions, the potential differences measured were found to agree closely with the one calculated for membranes ideally ion-selective for the cation species. The range of ideal performanee existed from p H 4 to 10 and ionic strengths from 3 X to 15. The choice of 50 layers was made because thicker films tended to be imperfect and thinner ones exhibited too high ohmic impedances. The resistance of a typical membrane (2 em. x 2500 A.) ranged from 20 to 60 megohms and thus high impedance instruments were employed as for glass electrode measurements. The individual electrodes fell into two simple classes: those which were ideally selective and those which did not work a t all. The defective elecVOL. 32, NO. 5, APRIL 1960
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