ACKNOWLEDGMENT
(5) W. B. Barnett and J. D. Kerber, At. Abs. News/., 13, 56 (1974).
LITERATURE CITED
(6) ASTM E387-69T, "Manual on Recommended Practices in Spectrophotometry", 3rd edition, American Society for Testing and Materials, Philadelphia, Pa., 1969. (7) V. A. Fassel, J. 0. Rasmuson,and T. G. Cowley, Spectrochim. Acfa,Part E, 23,579 (1968). (8) NBS Monograph 145, Part II, "Tables of Spectral-Line Intensities". U.S. Government Printing Office, Washington,D.C., 1975. (9) "Flame Emission and Atomic Absorption Spectrometry", Vol. 3, J. A. Dean and T. C. Rains, Ed., Marcel Dekker, New York, N,Y.. 1975.
( 1 ) H. L. Kahn and D. C. Manning, Am. Lab., 4 (8),51 (1972). (2) T. C. Rains, M. S. Epstein, and 0. Menis, Anal. Chern., 46, 207 (1974). (3) M. S. Epstein, T. C. Rains, and 0. Menis, Paper I f , 15th Eastern Analytical Symposium and 12th National Meeting of the Society for Applied Spectroscopy,New York, N.Y., 1973. (4) J. 0. Ingle. Jr., Anal. Chem., 46, 2161 (1974).
RECEIVEDfor review October 23, 1975. Accepted November 19, 1975. In no instance does the identification of commercial products imply recommendation or endorsement by the National Bureau of Standards.
T h e authors are indebted t o K. D. Mielenz of the National Bureau of Standards and A. T. Zander of t h e University of Maryland for their advice in the preparation of this manuscript.
Determination of Platinum and Palladium in Oxidation Catalysts for Automotive Exhaust by Atomic Absorption Spectrometry Noel M. Potter Analytical Chemistry Department, Research Laboratories, General Motors Corporation, Warren, Mich. 48090
A chemical method of analysis, capable of measuring platinum and palladium in automotive catalyst material with an accuracy of f2%, is described. After dissolution of a representative sample of the material and separation of the noble metals from the substrate material, platinum and palladium are measured by atomic absorption. Radioactive tracers were used to verify completeness of the chemical separation. Synthetic solutions were analyzed to investigate potential sources of interferences in the atomic absorption spectrophotometric measurement. Finally, a precision study using ground catalyst material was performed; for both platinum and palladium, a relative standard deviation of approximately 1 % was found.
With the advent of the catalytic converter t o control a u tomotive hydrocarbon and carbon monoxide emissions, analytical methods are required to measure the platinum and palladium content of the catalyst materials. Because of t h e low levels of platinum (-0.05%) and palladium (-0.02%), sensitive techniques are required, while economic considerations necessitate methods capable of higher accuracy than is usually required for chemical analyses. Many studies have been undertaken t o develop methods for the determination of platinum and palladium, b u t most investigations have been concerned with either geological materials containing trace amounts of these elements, or synthetic solutions used to evaluate the feasibility of utilizing special reagents or techniques. Instrumental techniques such as x-ray fluorescence ( I ) , x-ray diffraction ( 2 ) , and emission spectrography ( I , 3) have been applied for the determination of platinum and palladium in a variety of materials including alumina-base reforming catalysts. However, for highly accurate work utilizing instrumental techniques, a comprehensive array of specially prepared standards, which would consider differences in t h e catalyst substrate material and all potential interferences, would be required. Experience gained in wet chemical analysis of reforming catalysts has shown t h a t complete recoveries of the noble metals are obtained when both the metal and support material are dissolved ( 4 ) .Fire assay procedures ( 4 ) have been
used t o separate noble metals from various matrix materials, b u t the equipment required for these procedures is not available in most laboratories. Because of the low levels of platinum and palladium, classical gravimetric procedures ( 5 ) could not be easily applied to this problem. A variety of attractive spectrophotometric procedures (6-9) appear in t h e literature, b u t most require t h a t the platinum and palladium be separated from each other as well as the sample solution. In a t least one case (IO),platinum and palladium have been determined in the same solution; however, t h e conditions for color development appear too stringent for the case of dissolved catalyst material. Various atomic absorption techniques applied t o the determination of platinum and palladium appear in the literature (I, I I ) . Each element can be measured in the presence of the other, and conditions for accurate measurement can be easily controlled, once platinum and palladium are separated from the matrix material. For these reasons, it was decided t o combine a chemical Separation with atomic absorption. Complete sample dissolution, followed by a chemical separation and atomic absorption measurement, resulted in a method for the accurate determination of platinum and palladium in automotive catalyst materials.
EXPERIMENTAL Apparatus and Operating Parameters. Membrane filters, Metricel Alpha-8, 0.2-w pore size, 47 mm in diameter, regenerated cellulose (Gelman Instrument Co.) were used to collect the precipitated platinum and palladium. Measurements were made using a Perkin-Elmer Model 403 atomic absorption spectrophotometer. Light sources were a Westinghouse Model WL 23474A platinum hollow cathode lamp operated at 1 2 mA and a Westinghouse Model WL 22969 palladium hollow cathode lamp operated at 14 mA. The platinum resonance line at 266.0 nm and palladium resonance line at 247.6 nm were used. The slit widths were set so that the spectral band pass was approximately 0.2 nm for platinum and 0.7 nm for palladium. A premix burner with a single 10-cm slot burner head was positioned 12 mm below the beam of the hollow cathode lamp. The air flow rate was adjusted to 25.2 l./min and the acetylene flow rate to 7.7 l./min. Solution aspiration rate was between 4 and 5 ml/min. Standards and Reagents. All chemicals used were ACS reagent grade. Stock solutions included: lanthanum (100 g/l.), containing 117 g of La203 and 240 ml of HC1 per liter; stannous chloride (250 g/l.), containing 250 g of SnC12.2H20 and 500 ml of HC1 per liter; ANALYTICAL CHEMISTRY, VOL. 48, NO. 3, MARCH 1976
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Table I. Evaluation of the Precipitation of Pt and Pd with SnC1, (Te) Using Radioactive Tracers Element
Pd
Added, mg Found in filtrate and wash, mg Found o n filtering apparatus, mg
3.00
