Application. These organic acids in magnesium acetate medium (pH 4.5 or 6.8) can be determined without the interference by excessive of MgZf ion (Table 11). This method, therefore, could be used to study the application of magnesium acetate as an eluant in the separations of organic acids including oxalic acid by a strongly basic anion-exchanger (Dowex 1-XS). The ferric salicylate complex was also studied for the determination of some organic acids following the same procedures mentioned previously in the case of ferric 5-nitrosalicylate.
Ferric salicylate has reddish violet color within the pH range of 2.5 to 3.0 and has an absorbance maximum at 530 mp. The results of tartronic and I-ascorbic acids by ferric salicylate complex were much less accurate but malic acid and tartaric acid can be determined with good accuracy, compared to those by ferric 5-nitrosalicylate complex.
RECEIVED for review January 15, 1968. Accepted July 11, 1968. Work supported by the Ministry of Education of Korea for which the authors express their gratitude.
Consecutive Determination of Alkali Metal Bromides and Thiocyanates in Mixtures James E. Burroughs and Alan I. Attia Bosg- Warner Cnrp., Roy C. Ingessoll Research Center, Des Plaines, 111. 60018 ONEof the most accurate volumetric methods for determining alkali metal thiocyanates in the presence of halogens is the one proposed by Schulek ( I ) . This technique, which is based on the use of bromine t o oxidize the thiocyanate t o bromine cyanide followed by iodometry, does not permit the direct determination of bromides and thiocyanates in a single sample. Kolthoff (2) reported that thiocyanates could be determined gravimetrically as cuprous thiocyanates, the details of which may be found in general analytical texts (3). A review of the literature failed to indicate any attempts to utilize this fact t o selectively separate thiocyanate from bromides in their mixtures. Thiocyanates and bromides have been successfully identified in their mixtures after destructive oxidation of the thiocyanates with peroxides ( 4 ) . The present studies resulted in the development of a rapid, accurate, and successive determination of bromide and thiocyanate in mixtures with a single standard solution of AgN03. A potentiometric end point permits the application of the method to highly colored solutions. EXPERIMENTAL
Apparatus. A sulfide specific ion electrode (Model 94-16, Orion Research) and a standard fiber junction calomel electrode in contact with a 1M N a N 0 3 salt bridge were used with a recording p H meter (Model EUW-301, Heath Co.) to determine end points. Alternately, a glass-Ag/AgCl electrode system could be utilized. Reagents. All reagents were of analytical grade quality or better, and used without additional treatment. To establish the accuracy of the method, standard stock solutions of KBr and NH4SCN were used. Procedure. A solid or liquid sample, containing no more than 100 mg of the alkali metal thiocyanate and 250 mg of the alkali metal bromide, was weighed by difference into a 150-nil beaker. The sample was dissolved in about 40 ml of deionized water and acidified with 1-2 drops of 6N “ 0 3 . After complete dissolution, about 20 ml of 0.1M (CH3(I) E. Schulek, Z. Anal. Ciiem., 62, 337 (1923). (2) I. M. Kolthoff and P. J. Elving, Eds., “Treatise on Analytical Chemistry, Analytical Chemistry of the Elements,” Part 11, Vol. 7 , Interscience, New York, N. Y . , 1961, p 90. (3) F. P. Treadwell and W. T. Hall, “AnaIytical Chemistry,” Vol. 11, 9th Ed., Wiley, New York, N. Y . , 1955, p 303. (4) I. M. Kolthoff and V. A. Stenger, “Volumetric Analysis,” Vol. 11, Interscience, New York, N. Y . , 1957.
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COO)z.C u H20, followed by 0.25 gram of L-ascorbic acid, were added. The solution was mixed well, after which 10 drops of 0 . 2 z (w/v) of a phenol red solution were added. Concentrated “,OH was added dropwise until one drop imparted a distinct color change of the solution from yellow to red. About 3 ml of the “?OH were added in excess. After about five minutes of mixing on a magnetic stirring apparatus, dilute HN03(6N) was added dropwise until the solution was definitely orange (pH 7-8). One half of a n ashless filter tablet was added and mixed well with the solution. After allowing five minutes for the precipitation to be completed, the solution was filtered through a n S&S White Label filter paper, the filtrate being caught in a 250-ml beaker. The precipitate was washed three times with 10-ml portions of deionized water. The volume of the filtrate was adjusted to 125-150 ml with deionized water. To this solution was added in succession, with mixing, 5 ml concd H N O I and 10 ml of 2 0 x (w/v) Fe(N03)3.9 H 2 0 solution. After mixing for five minutes, the bromide content was determined by titration with a standard 0.1N A g N 0 3 solution, with the sulfide specific ion electrode to determine the end point. The filter paper containing the precipitated CuSCN, from above, was transferred to a 250-ml beaker and diluted with 125 ml of deionized water. About 5 ml concd H N 0 3 and 10 ml of 2 0 z (w/v) Fe(NOJ3.9H?O solution were added. After mixing for five minutes, the thiocyanate content was determined by the same procedure used for the bromide. DISCUSSIOh
This method takes advantage of the differences in the solubilities of CuBr and CuSCN in ammoniacal solutions. Cuprous bromide is soluble in excess NHiOH while cuprous thiocyanate is insoluble, affording a rapid and complete separation of the two anions. The analytical applications of ascorbic acid (which is not an acid at all, but a lactone) have been reviewed by Erdey and Svehla (5) and discussed by Belcher and Wilson ( 6 ) . In the present studies, ascorbic acid was employed for the generation in situ of cuprous ions from cupric acetate, resulting in the formation of a CuSCN precipitate which was more easily filtered. In order to circumvent the simultaneous precipitation ( 5 ) L. Erdey and G. Svehla, Chemist-Andyst, 52,24 (1963). (6) R. Belcher and C. L. Wilson, “New Methods of Analytical Chemistry,” Chapman and Hall Ltd., London, 1966, Chap 111.
of CuBr with CuSCN, studies were made that showed that CuBr is completely solubilized by the N H 10H-HNO:j treatment while CuSCN remains analytically insoluble. The final pH adjustment prior to the filtration was found to be a critical factor in achieving the separation. Standard mixtures, containing from 50-220 mg KBr and 100 mg NH4SCN, were analyzed by the proposed procedure. The results are shown in Table I (7, 8). The data clearly indicate that this method is equivalent in precision and accuracy to the classical Volhard method ( 9 ) as applied to pure bromide or thiocyanate solutions. Furthermore, only a single titrant is required, minimizing potential sources of error. The relative merits of the sulfide specific ion electrode as an indicator electrode for argentometric titrations have been investigated and reported (Orion Research Inc., Cambridge, (7) IUPAC Information Bulletin No. 26, August 1966. (8) W. J . Youden; “Statistical Methods for Chemists,” Wiley, New Yorh, N. Y . . 1951. (9) E. H. Swii‘t, G. M. Arcand, R. Lutwack, and D. J . Meier, ANAL.CHEV.: 22, 306. 1950.
Table I.
Recovery Data for Mixtures of KBr and KSCN Compot~nd KBr KSCN Number of analqses 7 7 Mean value 99.64 99.61 Median value 99.60 99.50 Range 0.70 1.50 Mean deviation 0.25 0.37 Per cent variation 0.25 0.37 Standard deviation 0.27 0.46
Mass). The salt bridge for the calomel reference electrode was used t o prevent chloride contamination and to prevent clogging the fiber junction with insoluble silver salts. The end point in the present procedure was occasioned by a potential change of about 50--60 mV per drop (0.03 mi) of 0.1N AgNO,{. RECEIVED for review May 29, 1968. Accepted August 2, 1968.
Spectrophotometric Determination of Silver(1) in Nonaqueous Solutions by Oxidative Coupling of Aromatic Amines Robert I,. Rebertus and Vaughn Levin Central Research Laboratories, Minnesofa Mining and Munufacfuring Co., St. Puul, Minn. 55101
SPECTROPHOTOMETRIC methods for determining silver(1) ion are usually based upon complexation reactions with ligands such as dithizone ( I ) , p-dimethylaminobenzalrhodanine( I ) , toluene-3,4-dithiol (2), 2-amino-6-methylthio-4-pyrimidine-carboxylic acid (3), or 4,4’-bis(diniethy1amino)thiobenzophenone ( 4 ) . Generally, the reported procedures apply only to aqueous solutions of the silver. In the present study we have demonstrated that oxidation-reduction reactions, similar to the coupling reactions employed in some color photographic processes ( 5 ) , are useful for the determination of silver(1) in nonaqueous solvents. In particular, the four-electron oxidation of equimolar mixtures of 111- and p-phenylenediamine permits the rapid and convenient spectrophotometric determination of silver(1) in the concentration range, 1 to 10 pg/ml, in alcohols, acetone, toluene, or ethyl acetate. EXPERIMENT 4 L
Apparatus. Spectra and absorbance measurements were made with a Beckmm Grating Spectrophotometer, Model DB-G. Matched cells with a 1-cm optical path were used. Reagents and Chemicals. m-Phenylenediamine, p-phenylenediamine, N,N-dimethyl-p-phenylenediamine,and toluene-
(1) E. P. Przybylowicz and C. W. Zuehlke, in “Treatise on Analytical Chemistry,” Part 11, Vol. 4, I. M. Kolthoff and P. J. Elving, Eds., Interscience, New York, 1966, pp 61-3. (2) J. P. Dux and W. R. Feairheller, ANAL.CHEhi., 33, 445 (1961). (3) 0. K . Chung and C. E. Meloan, ibid., 39, 383 (1967). (4) K . L. Cheng, Mikrochitn. Acta, 1967, 820. ( 5 ) G. F. Duffin, “Photographic Emulsion Chemistry,” The Focal Press, London-New York, 1966, pp 190-4.
2,4-diamine, all practical grade, were obtained from Eastman Kodak Co. Procedure for Methanol and Other Solvents. To a 10-ml volumetric flask equipped with a small reflux condenser are added 5 ml of methanol containing silver(I), 1 nil of 0.1M sodium acetate in methanol, 1 ml of in-phenylenediamine solution (1 gram/liter in methanol), and 1 ml of p-phenylenediamine solution (1 gram/liter in methanol). The solution is boiled for 10 minutes, cooled, diluted to volume, and filtered through a Whatman No. 5 filter paper. The first portion of the filtrate is discarded, after which the optical cell is filled and the spectrum measured. Calibration data are obtained from diluted aliquots of 0.0015M solution of silver nitrate in methanol. I n this procedure, toluene-2,4diamine and N,N-dimethyl-p-phenylenediamine may be substituted for rn-phenylenediamine and p-phenylenediamine, respectively . The procedure for determining silver(1) in isopropanol or acetone is similar to that for methanol except that the periods of time for color development are different. The reaction time for isopropanol is 5 minutes at the boiling point, and that for acetone is 1 minute at 25 “C. Water solutions require a pH 7 buffer and a color development period of 5 minutes at 25 “C. In order to analyze solutions of silver(1) in ethyl acetate, it is necessary to introduce the reagents in methanol and to dilute the ethyl acetate to a final concentration of 50% (v/v) ethyl acetate-methanol. Color development is then complete within 10 minutes. Solutions of silver(1) in toluene are handled by introducing the reagents in isopropanol, diluting with isopropanol and wzter to a final composition of toluene (50 vol %)-isopropanol (49.5 vol %)-water (0.5 vol Z), and allowing 1 minute for color development. VOL. 40, NO. 13, NOVEMBER 1968
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