Indirect Spectrophotometric Determination of PaIladium(II) with 2,1,3Benzoselenadiazole Thomas G . Bunting’ and Clifton E. Meloan Department of Chemistry, Kansas State University, Manhattan, Kan.
A WIDE VARIETY of reagents for the determination of palladium have been described ( I ) . Although used in an indirect method, the reagent described below is more selective than most reagents, while the procedure is certainly the least complicated described to date. In the present work, 2,1,3-benzoselenadiazole(hereafter, piaselenol), first described by Hinsberg (2), was found to be applicable to determination of traces of palladium. The reaction of palladium with piaselenol was described by Ziegler and Glemser (3). Palladous chloride and piaselenol react to give a yellow precipitate insoluble in all common solvents. Elemental analysis and mole ratio studies (4) showed that the ratio of palladous chloride to piaselenol in the precipitate is 1 mole to 2 moles, respectively. Absorbance measurements of the excess reagent were made at the wavelength of maximum absorbance, 330 mp. The molar absorptivity of the reagent in 50-50 (volume) ethanolwater solution was 1.9 x lo4.
Table I. Precision and Accuracy Palladium(II), ppm Added” Found* 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 1.000
0,099 0.202 0.295 0.398 0.510 0.612 0.721 0.798 0.895 0.992
Recovery, 99.0 101.o 98.3 99.5 102.0 102.0 103.0 99.8 99.4 99.2 100.4
b
0.498 ppm Pd(I1) in sample. Averages of triplicates.
EXPERIMENTAL
Apparatus. Spectral studies were performed with a Beckman Model DB spectrophotometer and 1.OO-cm matched quartz cells. Preparation of Reagent. The procedure of Hinsberg (2) was employed to prepare piaselenol from o-phenylene diamine dihydrochloride (J. T. Baker T653) and selenous acid (Fisher A-286). Reagent Solution. Piaselenol(2.4830 grams was) dissolved in 250 ml of absolute EtOH and diluted with absolute EtOH as required. The solution is stable indefinitely. Standard Solutions. All chemicals used were reagent grade. The standard palladium solution was prepared by dissolving palladous chloride in 1N HC1. The palladium solution was standardized by precipitation with dimethylglyoxime (5). Procedure. A 5-ml aliquot of the sample was added to a 20-ml centrifuge tube; 5 ml of standard piaselenol was added with thorough mixing. The resulting mixture was centrifuged for 5 minutes, after which the supernatant liquid was decanted into a 1-00-cm quartz spectrophotometer cell and the absorbance was measured at 330 mp. RESULTS
Effect of Time. The yellow precipitate of palladous chloride forms immediately. The system is stable indefinitely. Present address, Esso Research and Engineering Co., Linden, N.J. (1) F. E. Beamish, Talartra, 12, 743 (1965). (2) 0. Hinsberg, Chem. Ber., 22,2895 (1889). (3) M. Ziegler and 0. Glemser, 2.Anal. Chem., 146, 29 (1955). (4) J. H. Yoe, and A. L. Jones, IND.ENG.CHEM., ANAL.ED., 16, 111 (1944). (5) S. A. Reed and C . V. Banks, Proc. Iowa Acad. Sci., 55, 267 (1948).
Precision and Accuracy. Results of accuracy studies are summarized in Table I. A sample containing about 5 % Pd on CaC03 (American Platinum Works) was dissolved in aqua regia and diluted with 1N HC1 to give a Pd(I1) concentration of about 1 ppm. Analysis of 12 aliquots of this sample using the above procedure gave a value of 4.99 ==I 0.14% for the palladium content. This is a relative standard deviation of 2.8 %. Beer’s Law and Sensitivity. A straight line was obtained over the range 0.1-5.0 ppm of palladium. Using Sandell’s definition of sensitivity (6) the method has a sensitivity of 0.003 ,.g/cm2. However, the excess of piaselenol required to suppress the solubility of the palladium precipitate limits the practical sensitivity to about 10 ppb. Effect of Diverse Ions. One milligram of a foreign ion was added to a sample containing 1 ppm of palladium(I1). With the procedure outlined above, no interference was noted for the following ions: Ag+, A13+, Au31, Ba2+, Ca2+, Coz+, Crest Cu2+, Fe3+,Mood2-,Niz+, PbZS,PtCIZ-, Rh3+, Ru3+, Si032-, Sr2+,Te4+,Th4+,Tl3+, V03-, Y3*,Zr4+,Br-, C1-, Cz042-,I-, NO3-, and Sod2-. CdZ+ slowly forms a precipitate with piaselenol so that interference from Cd2+ is time dependent. Ce4+, Hg2+, and Ti4+ all determine as palladium, Ce4+ and Ti4+ give a white precipitate while Hg2+gives a yellow precipitate. CN- and SCN- both prevent the precipitation of the palladous chloride-piaselenol compound. RECEIVED for review November 3,1967.
Accepted November
20,1967. (6) E. B. Sandell, “Colorimetric Determination of Traces of Metals,” 3rd Ed., Interscience, New York, 1959, p 80.
VOL 40, NO. 2, FEBRUARY 1968
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