V O L U M E 2 1 , N O . 1, J A N U A R Y 1 9 4 9 (37) Schmidt, R., 2.ges. Schiess.- u . Sprengstoffw. Nitrocellulose, 38, 148 (1943). (38) Seaman, W., Norton, A. R., Woods, J. T., and Bank, H. N., J . Am. Chem. SOC.,67, 1571 (1945). (39) Shiraeff, D. A., Am. Dyestuf Reptr., 36, No. 12, Proc. Am. Assoc. Textile Chem. Colorists, 313 (1947). (40) Simmons, M. C., ANAL.CHEM.,19, 385 (1947). (41) Soeai, J. A., Analesfarm. u bioqulm. (Buenos Aires), 14, 41 (1943). (42) Stagg, H. E., Analyst, 71, 557 (1946). (43) Tunnicliff, D. D., Peters, E. D., Lykken, L., and Tuemmler, F. D., Ibid., 18, 710 (1946). (44) Vandoni, R., M e m . serz'ices chim. itat, 30, 18 (1943).
163 (45) Ibid., 30, 272 (1943). (46) Williams, K. T., and Johnson, C. M., IND.ENG.CHEM.,ANAL. ED., 16, 23 (1944). (47) Willits, C. O., ANAL.CHEU.,21, 132 (1949). (48) Wise, L. E., and McCammon, D.C., J . Assoc. Oficial Agr. Chem., 28, 167 (1945). (49) Wise, L. E., and Ratliff, E. K., ANAL.CHEM.,19, 694 (1947). (50) Zavarov, G. V., Khimicheskaya Prom., 1945, No. 2, 21. (51) Zimmermann, W., Mikrochemie ver. Mikrochim. Acta, 31, 140 (1943). RECEIVED November 23, 1948.
INORGANIC VOLUMETRIC ANALYSIS CLEMENT J. RODDEN National Bureau of Standards, Washington, D . C .
V"""'
I I E T R I C methods 89 applied t o inorganic analysis have seen, in the past several years, the usual modifications a n d reviews of existing methods, as well as some that are new and novel. Several innovations and improvements of existing apparatus have been made. Publications describing the results of European workers have been received irregularly. As a result, references are incomplete; hoyever, the work of Russian workers since the end of World War I1 has been discussed in French (212).
TITRATION
Reviews and examinations include a tsxt'book on titration methods (96); the precise measurements of volume (201); procedures and techniques for colorimetric titrations with photoelectric instruments (216 ) ; apparatus and techniques for amperometric titrations (191); potentiometric titration methods with special attention to microchemical applications (145, 192) and to arsenic and iron (62); new and existing methods for tungsten (26,146),thorium (139),and vanadium (148); potassium as cobaltinitrite, chiefly in plant ash (208); cobalt in steel by ferricyanide (8); the effect of iron in the reduction of molybdate in determining phosphorus (129) ; the Karl Fischer procedure for water (37, 177); and the iodomctric determination of thionalide as applied to bismuth, mercury, and copper (101). A discussion of the strength of acids in various organic solvents is of interest (224). A graphic procedure has been advocated as a means of determining the results of volumetric analysis (207). Apparatus and accessories (142) for automatic titrations, whereby it is only necessary to prepare and load feed units, have been described (118) and are on the market (157). The automatic recording of titrations as applied to potentiometric, amperometric, and absorptiometric titration has been made with recording potentiometers (73). Further work on the use of high frequency oscillators ( 8 7 ) ,which at one time promised to revolutionize volumetric analysis, has not been found. A simple apparatus, requiring only a battery, a microammeter, a variable resistance, and silver and copper wires for electrodes has been used with good results for the rapid analysis of chloride (49). Apparatus for polarization dead-stop end points has been described (58) n-hich is essentiallj- that of earlier n-orkers ( 6 5 ) . -4 cell suitable for conductivity determination of chloride in sea water is useful as a time-saver ( 4 ) . Titrations have been made using photoelectric colorimeters (160) which are a further application of previous work (149, 217). Among the several types of burets that have been suggested, are a n electrical solenoidoperated buret which avoids stopcocks but may be prone to leak ( 1 4 5 ) ; a rather complicated microburet, controlled by addition of
water to a mercury level (274); a syringe microburet (181); and a micropipet for titration of microgram samples (125). An 89sentially new technique for operation of a microburet appears useful (167). Electronically controlled apparatus for distillation of fluoride or hydrofluosilicic acid (218) is an important improvement. Several variations from the usual run of the mill methods are of interest. Among these are titrations in strongly colored solution by adding a solution of a complementary color ( 2 0 ) ; titration of dark colored solutions by extracting with ether prior to titration ( 9 9 ) ; extracting sulfuric acid from crude sulfonic acids with n-amyl alcohol, which is then extracted with water prior to titration (47); and titrating fuming sulfuric acid with water a t 10" C. (19). Aluminum has been determined in pigments by dissolving in ferric sulfate solution followed by permanganate titration (116). Free alkali in plating solutions is determined by adding excess barium chloride and alcohol and titrating to a phenolphthalein end point; after filtering, the precipitate is titrated with hydrochloric acid (184). hlagnesium can be titrated as oxalate after precipitation from 85y0 acetic acid with ethyl oxalate (76). Luminescent titrat,ion under ultraviolet radiation has been used to determine lead with sodium oxalate using fluorescein 89 an indicator (92). The use of photoelectric instruments instead of the eye for determination of end points (127), both colorimetric (127, 1 3 6 , 161, 217) and turbidimetric (43), has increased in Europe. Use has been made of anionic agents to titrate cationic agents and vice versa with appearance of turbidity a t the end point (102). The effect of various salts and acids on the iodometric estimation of persulfate and vanadate has been investigated. By adding cuprous iodide, oxalic acid, or ferrous sulfate, reactions are catalyzed to such an extent that iodometric determinations of persulfate and vanadate can be made ( 1 6 1 - 1 6 4 ) . Aniperometric titration of dilute chromate solutions (95) is another application of the interesting rotating platinum electrode. Determinations of arsenic by coulometric titration by electrically generated bromine using an amperometric end point have been made (144). Potentiometric methods have been advocated for beryllium by titrating with sodium fluoride (199); selenium and tellurium with chromous ion (125'); nitric acid in oleum (128); phosphate by an indirect method ( 6 3 ); and thorium with potassium iodate (190). .4n important study on conditions for potentiometric titration of titanium has been made using a mercury indicating electrode (119). When traces of certain elements are to be determined, the dithizone titration technique has been used for copper ( l 7 6 ) ,lead in copper, nickel, and cobalt ( 2 S 6 ) , nickel (227) and zinc (225) in cobalt. Another extraction method extracts iodine with chloro-
164
ANALYTICAL CHEMISTRY
form, adds water, and titrates with thiosulfate in the determination of ferric compounds (200). STANDARD SOLUTIONS AND REAGENTS
The question of standard solutions and reagents for analysis is always of considerable importance. Variations of standardiaation methods have been examined for iodine ( l o ) ,and for thiosulfate, thiocyanate. and permanganate solutions (211). Rlolybdenum (V) as a volumetric reagent shows considerable promise (203). Methods of storing and dispensing oxygen-sensitive solutions (lZ4,193, $05) and the use of chromous solutions have been critically examined (119, 123, 206). The direct titration of acidified arsenic solutions with dichromate has been stated to give high results (156). Five leading brands of reagent grade sodium carbonate were found to have purity satisfactory for a standard reference (31). The use of sulfamic acid as an acidimetric standard has increased. Ferrous ethylenediamine sulfate shows promise &s an oxidimetric standard (29). The following reagents are of interest: metallic silver as a fundamental standard in acidimetry (68); substitutes (143); mercurous perchlorate for iron (158); phosphate (98) and ammonium vanadate (207) for many elements; chloramine-T for tin (48); 8-hydroxyquinaldine in place of 8-hydroxyquinone (135); potassium chlorostannate for vanadium and molybdenum (88); ferrocyanide as a reducing agent (186); naphthyloxychlorophosphine for water ( 117) ; and iminodiacetic acid for hardness of water (179). The use of starch to prevent precipitation of thorium fluoride in the titration of fluoride has been advocated (194). The preparation of silver for use in the silver reductor has been described (187). INDICATORS
Several new indicators have been suggested and the usual variations of the old ones have appeared. Solochrome Brilliant Blue has been used with thorium in the estimation of fluoride (138). A sodium salt of starch glycolic acid (151) and amylose (115) appear to be more useful than the usual starch solution in iodometric analysis. Suggested for argcntometric titrations have been p-dimethylaminobenaylidenerhodanine (76), resorcinolsuccinein ( l a $ , phenolphthalein ( I S l ) , and mercurous ion and diphenylcarbazone (70). Indicators of special interest are 2, 2’-bipyridine ferrous complex ion, which is less expensive than other reagents of this group (28), derivatives of diphenylaminesulfonic acid for titrating arsenite in alkaline solutions ( M 7 ) , phenylanthranilic acid in the method whereby Mo (VI) is reduced to h40 (V) (64); diphenylcarbazone for zinc and nickel (55, 57); and eriochromeschwarz in the “complexometric” titration of alkaline salts (15). Other workers have used cochineal with hypochlorite (17); 1-naphthol for iron ( 1 ) ; and cacotheline for calcium and iron (91). The acidimetric titration indicators suggested are modified methyl orange for direct titration of sodium carbonate (SO), disulfonates for alkalinity of water (198), and emodin for weak acids and bases (d10). Cellosolve has been advocated as a solvent for phenolphthalein, as it does not evaporate like ethyl alcohol (84). ANALYSIS OF ELEMEKTS
I n methods as applied to individual elements there are some innovations, FLS well as application of time-worn methods:
Aluminum. Determined in aluminum pigments by dissolving in ferric ion solution and titrating ferrous ion formed (149); fluoride titration with ferrous ion and thiocyanate as indicator (168) or in neutralized tartrate solution (189); a rather complicated procedure based on fluoride complex formation (79); oxine with bromometric estimation in titanium pigments ( 9 ); acidimetric titration of aluminate ion with hydrochloric acid using a potentiometric end point (fir),as well &s a basic titration using alkali and a rrlass electrode 1100). Antimony. Separation by volatilization followed by the usual bromate titration (86, 107).
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Arsenic. Coulometric titration (144); with cerate ion in perchloric acid (188); iodometrically on arsenic trioxide in arsenic (IO$), on the chloride after separation by volatilization (150), on arsenic ions after coprecipitation with magnesium ammonium phosphate (93), and after precipitation of elemental arsenic by hypophosphorous acid (66); hypobromite titration of arsenite in alkaline solution, with the new diphenylamine sulfonic acid indicators (217); and a simplified bromate method (85). I n the presence of catalysts such as rhenium, arsenate is reduced with stannous chloride in the presence of tartaric acid before iodometric titration (204). Barium. Amperometric titration of chromate in ethanol solution (94); phosphate titration (98); and ignition of carboxylic acid salts to carbonate followed by addition of hydrochloric acid (183). Beryllium. Potentiometric titration with sodium fluoride (199). Cadmium. Determined potentiometrically with alkali (JS), and by a rather involved silver sulfide method (106). Calcium. Modifications of existing oxalate-permanganate methods (72, 120). A method employing cacotheline as indicator appears to be satisfactory (91). Cerium. N-phenylanthranilic acid is recommended as indicator (40). Chromium. Electrometric titration involving the Pt/HaPOa/ Hg2HP04/Hg electrode gives excellent results in steel (16). Perchloric acid oxidation for thorium-chromium mixtures (69); an apparatus for retaining chromyl chloride when using perchloric acid oxidation (178); and variations in time-honored methods (14,18, 52, 147, 170, 171, 202). Cobalt. Cyanide and ferricyanide methods are examined critically (8,87). Ferricyanide titration in alloys (44, 80). Columbium. In complex salts by alkalimetric titration (95); reduction in Jones reductor followed by permanganate titration (67). Copper. Extractive titration with dithiaone ( 176); determination of cuprous ion by titrating with permanganate, dichromate, or ceric sulfate (83); a new method whereby cuprous thiocyanate is precipitated after reduction with sulfur dioxide, dissolved in ferric alum, and the ferrous ion formed is titrated (24). Fluorine. Titration with alumium chloride using Eriochromcyanine R as an indicator (175); modifications of existing methods using alizarin sulfonate (90, 231) or Solochrome Brilliant Blue (138). Starch has been used to prevent the formation of thorium tetrafluoride in the titration with thorium nitrate (194). Germanium. Hypophosphite is used to reduce GeCL to GeC12 followed by iodometric titration (86). Gold. Reduction with standard ferrous ion followed by permanganate (209) ; instead of weighing after formaldehyde reduction, dissolving in standard iodide and back-titrating with thiosulfate (113). Halides and Halates. Determination of hydrochloric acid in presence of chlorine by boiling to remove chlorine and titrating hydrochloric acid with alkali (12) ; chloride by amperometric method (81), conductometric ( 4 ) , and potentiometric (49) titration with indicator by extracting color into ether (76),modification of Berg’s method ($13); interesting method by reaction of soluble chlorides with solid mercurous iodate and, after filtering, by iodometric titration of precipitate with thiosulfate ( 7 ); chloride after adding thiocyanate and ferric nitrate, titrating with mercuric nitrate (154); chlorates by titrating with methyl orange solution (41), iodometric (ddO), ferrous sulfate reduction (2191,or Volhard method after bomb reduction (194); reaction of hypochlorite with hydrazine sulfate, which is then back-titrated with hypochlorite solution (36); chlorate and hypochlorite with sodium benzene sulfinate (6); hypochlorite and hypobromite based on selective reduction of hypobromite with alkaline phenol (60); iodide by automatic titration (118) and by thiosulfate a t controlled pH (6). Iron. Ferrous ion determined in presence of thiocyanate by complexing thiocyanate with mercuric nitrate before titration with dichromate or permanganate ($3). 2, 2’-Bipyridine ferrous complex indicator with cerate titration gives excellent results (28). Cacotheline as indicator gives acceptable results by using stannous chloride to titrate ferrous ion (91); ferric ion in ferrous lactate and tartrate by liberating iodine in bicarbonate with potassium iodide, extracting with chloroform, and then adding water and titrating with thiosulfate ($00). Mercurous perchlorate has been suggested as a volumetric reagent but results are not stoichiometric (168). Application of the cerate titration to micro amounts has given results as good as colorimetric in t h e 100- to 500-microgram range (188). Automatic titrations have been made using cerate (118) and chromous ion (119). Applications of existing methods (67, 171 207) ~
V O L U M E 21, NO. 1, J A N U A R Y 1 9 4 9 Lead. Luminescent titration with sodium oxalate and fluorescein (92); potentiometric titration with alkali fluoride by precipitating chlorofluoride, end point given by drop in ferric-ferrous .oxidation reduction potential (61); dithizone extraction titration (226); as iodate (38,7 1 ) ; and as molybdate (159). Magnesium. Good results are obtained by using the slow decomposition of ethyl oxalate in 85y0acetic acid, the oxalate being precipitated in a form suitable for filtration and titration with permanganate (76); variations of existing methods by precipitating with standard alkali, filtering, and titrating excess alkali (222), adding alkali to pink color of trinitrobenzene and backtitrating with hydrochloric acid to phenolphthalein end point (45); in aluminum alloys (50). Manganese. I n a new method with few interferences, a neutral manganous pyrophosphate solution is titrated potentiometrically with permanganate to give a pyrophosphate complex (121'r . For solutions brightly colored with nickel, permanganate is titrated with ferrous ion using diphenylamine as indicator (112). Titration with phosphate for rough lvork (97). Mercury. Modification of methods whereby mercurous ion is determined iodometrically and total mercury by cerate oxidation followed by thiocyanate titration (215); mercuric oxide by reaction with potassium thiocyanate instead of potassiam iodide to form potassium hydroxide, which is titrated ($6); stannous .chloride reduction (13); precipitation by iodate and iodometric determination on precipitate after filtration (39, 69). Molybdenum. I n a reduction of Mo (VI) to Mo (V) with mercury instead of hlo (111)with zinc amalgam, solutions are not oxidized by air and vanadium does not interfere (64). Jn mixtures with vanadium by sulfur dioxide reduction for vanadium follon-ed by zinc reduction for molybdenum and vanadium (34); acidimetric and barium salt titration (78); replacement of stannous chloride by KZSnCl4for reduction recommended (88); precipitation with 8-hydroffyquinoline follolved by usual bromometric titration (8, 140). Nickel. Extraction methods usins dithizone titration for small amounts (227); extraction into amyl alcohol with diphenylcarbazone followed by cyanide titration (55); oxine precipitation followed by iodometric (141); cyanide titration in steel (18, 170). Nitrogen. Study of various procedures for nitrogen in r e fractory metal carbides (165); determination of nitrites by adding excess of hypochlorite and back-titrating with potassium iodide (52); nitric acid in oleum by electrometric titration (128). Nitrates are reduced by ferrous sulfate and silver nitrate in the Kjeldahl method (46); nitrates by treating with standard ferrous sulfate followed by back-titrating with dichromate (108, 111). Phosphate. Argentometric potentiometric titration a t pH 9 or determination by adding standard silver nitrate a t pH 7.5 and back-titrating with potassium bromide (22, 63) ; alkali titration (110). Phosphomolybdate precipitate is dissolved in standard alkali and back-titrated with sulfuric acid (82); complicated bismuth precipitation finished by iodometric titration (74); alum or ferric chloride titration (153). Platinum. Reduction of Pt (IV) to P t (11)by titrating with standard ferrous ion under carbon dioxide, then titrating excess with ammonium vanadate, using phenylanthranlic acid as indicator. Can be used to determine alkalies (197). Potassium. Determined in sodium-potassium alloys by react,ing with absolute alcohol under neohexane followed by titration with standard acid (214); cobaltinitrite with permanganate (104); a review of cobaltinitrite methods with recommendations of ceric sulfate as titrant (208); periodate precipitation followed by arsenite titration (172). Rhodium. Oxidation to Rh (V) with sodium bismuthate and after filtering to remove bismuthate titrating with ferrous ion, using phenylanthranilic acid as indicator. Platinum does not interfere but iridium does (196). Selenium. Potentiometric titration with chromous ion in 9A'hydrochloric acid a t 60" to 70" C. (123),precipitation of silver selenate a t pH 7 with standard silver nitrate and after filtering, back-titrating with potassium chloride (169); precipitation of selenium followed by iodometric titration (54, 156). Silicon. Precipitation as yellow hexamethylenetetramine silicomolybdate. Precipitate is hydrolyzed in slightly acid solution to give formaldehyde and ammonia, which is treated with standard bisulfite and then back-titrated with iodine (6.9). Sodium. Variations of acidimetric method (166, 184); alkali determined in permanganate by reduction with acid solution of peroxide (126). Sulfur. Soluble sulfides can be titrated with ferricyanide a t pH 9.2 with ferrous dimethylgloxime complex as indicator ( 4 2 ) . Sulfur is distilled as hydrogen sulfide into excess calcium oxychloride and back-titrated iodometrically (152). Adaptation of knonm methods (2, 89, 109, 223); precipitation of sulfate as lead sulfate and, after filtering, titration of excess lead with ammonium molyb-
165 date (106). Persulfate can be titrated with iodine in presence of cuprous iodide as catalyst (162). Tellurium. Potentiometric titration with chromous ion (123). Thallium. Thallous ion can be titrated with potassium iodide, using bromophenol blue as indicator (152). Thorium. Iodate precipitation, followed by iodometric titration after filtering and dissolving, but not so accurate as gravimetric (130, 190); precipitation as molybdate which after filtering and dissolving is run through Jones reductor and b l o (111) titrated with cerate ion (11). Tin. Reduction with antimony (137)or nickel in a hot solution (185)followed by iodometric estimation. Titanium. Study of conditions for potentiometric titration of T i (IV) with chromous ion, using mercury indicator electrode (159). Tungsten. Investigation of variables in use of chromous solutions to reduce tungsten followed by back-titrating with dichromate (205). Solid barium thiosulfate monohydrate is used to precipitate tungsten in a neutral solution in ethyl alcohol, which is filtered, and thiosulfate in solution is titrated with iodine (173). Precipitation as 8-hydroxyquinoline followed by bromometric titration (8); review of existing methods ( 2 6 ) . Uranium. Uranyl ion is reduced electrolytically to U (IV) and titrated with cerate ion after oxidizing U (111) to Zi (IV) by air (195). Vanadium. Reduction study of V (V) to V (IV) in the silver reductor (162); 8-hydroxyquinoline precipitation followed by bromometric titration (8); ferrous ion titration of Cr (VI) and V (17) followed by oxidation of V (IV) to V (V) with permanganate and subsequent titration with ferrous ion (14, 5 2 ) ; variations in known methods for specific materials, steel ( l 7 1 ) , cemented carbides (206),and mixt,uics (34, 148). Water. Modification of Karl Fischer method in chloral (188), food (177). and lecithin (2f); liquid sulfur dioxide (6f);naval stores ( 7 7 ) . micromodification (114);review of methods ( 3 7 ) . Zinc. After complexing nickel with cyanide, amyl alcohol and carbon tetrachloride are added with diphenylcarbazone as indicator and carbon tetrachloride layer is titrated with ferrocyanide (55, 6 6 ) . Ferrocyanide modification (172, 180). Potentiometric titration with alkali suggested but may have difficulties in applying (33). Extractive titration with dithizone for small amounts (3, 625). ACKNOWLEDGMEYT
The author wishes to express his thanks to F. D. Haisten for assistance v-ith the bibliography. LITERATURE CITED (1) Airan, F. W., and Pandit, G. N., Current Sci. ( I n d i a ) , 15, 348 (1946). (2) .4limarin, I. P., and Sheskols'kaya, A. Ya., Zhur. Anal. Khim., 1, 166 (1946). (3) Analytical Methods Committee, Analyst, 73, 305 (1948). Anderson, L. J.,ANAL.CHEM.,20, 618 (1948). Arkel, C. G. van, and Sousbeck, J. J. M. van, Pharm. W r e k blad, 82, 520 (1947). Atkin, S., ANAL.CHEX.,19, 816 (1947). Avaliani, K.. Zavodskaya Lab., 12, 179 (1946). Bagshawe, B., and Hobson, J. D., Analyst, 73, 152 (1948). Baker, I., and ,Martin, G., IND. ENG.CHEM.,ANAL.ED.,17, 488 (1946). Banks, C. K., J. A m . Pharm. Assoc., Sci. Ed., 37, 6 (1948). Banks, C. V., and Diehl, H., ANAL.CHEM.,19,222 (1947). Barnham, H. N., and Thomson, T. R., Ibid., 20, 60 (1948). Bartlett, J. N.,and McNabb, W. M., Ibid., 19, 484 (1947). Berry, A. J., Analyst, 70, 371 (1945).
Biedermann, T. W., and Schwarsenbach, G., Chimia (Switz.), 2, 56 (1948).
Birckel, J., A n n . chim. anal., 26, 64 (1944). Bitskei. J., and Forhencs, M., Magyar Kdm. Lapja, 2, 117, 230 (1947).
Bogdanchenko, A. G., Zavodskaya Lab., 13, 748 (1947). Brand, J. C. D., J. Chem. Soc., 1946, 585. Brat, M., Chim. anal., 29, 85 (1947). Brost, I
