Loss of Gold during Sample Dissolution Herbert A. Moore and Robert A. Wessman Trapelol West, Diaision of LFE Corporation, Richmond,Calif. 94804 QUANTITATIVE ANALYSIS necessarily requires the absence of unpredictable material loss in all stages of an analysis procedure. In the analysis of samples approaching limits of detection, even predictable losses are undesirable. A number of mechanisms for loss are possible if the material of interest is bound in a matrix which must be decomposed prior to analysis. This paper presents the results from a n investigation of the loss of gold during dissolution of IPC paper with fuming H N 0 3and HCIO?. Gorsuch (1) has covered most of the literature relating to the recovery of group I B elements following destruction of organic matter. There is very little information available on the loss of gold during wet ashing of organic material. Smith ( 2 ) tested volatilization of 55 elements in a procedure wherein 20-100 mg of the element in HClO, was heated to 200-220 “C while hydrochloric acid was slowly added. In the case of gold, only 1 was found in the distillate. Hillebrand et d . (3) found that gold volatilizes somewhat from solutions of aqua regia when rapidly evaporated to dryness, or from aqua regia solutions treated with H 2 S 0 4and evaporated to copious fumes. Gijbels and Hoste ( 4 ) found that very little l98Au distilled from H2SO4-HC1O4-Ch at 200 “C following peroxide fusion, heating in H2S04-H202,or heating in H2S04-NaBr03. No reference was found on loss of gold during dissolution of cellulose material (IPC paper) with fuming H N 0 3 and HCI04. The results reported in this work show that significant amounts of gold are volatilized under the conditions of this dissolution. A report received subsequent to the preparation of this paper describes experiments which verify the volatilization of gold during dissolution of IPC paper with a mixture of HCI04, HN03,andHC1(5).
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EXPERIMENTAL Reagents and Materials. Gold-195 tracer was prepared by diluting 0.1 mCi 155Au produced by (d, 2n) reaction of Ig5Pt obtained, as carrier free (180 Ci/gram Au) auric chloride dissolved in 10M HCI, from the United Kingdom Atomic Energy Authority. Di(2-butoxyethyl) phthalate (“Kronisol”) was Matheson, Coleman and Bell practical grade. Test samples consisted of either 26-gram sheets of IPC 1478 impregnated with “Kronisol” (30 by weight) or other cellulose material represented by shredded sheets of No. 50 Whatman filter paper. All reagents were reagent grade. Instruments. Spectra were obtained with a Harshaw Model 6SSH5/2H-X 1.25-in. X 1.5-in. NaI(T1) detector and T M C Model 404C 400-channel pulse height analyzer. Gross counts were taken on a Tracerlab Model P20D gross gamma probe and Compu/Matic I1 scaler. ~
(1) T. T. Gorsuch, “The Destruction of Organic Matter,” Pergamon Press, New York, N.Y., 1970, pp 60-67. (2) G F. Smith, “Mixed Perchloric. Sulphuric and Phosphoric Acids and Their Applications in Analysis,” 2nd ed., The G. Frederick Smith Chemical Co., Columbus, Ohio, 1942, p 61. (3) W. Hillebrand, G. Lundell. H. Bright, and J. Hoffman, “Apdied Inorganic Analysis,” John Wiley and Sons, New York, N.Y.. 195% p 343. . (4)R. Giibels and J. Hoste. Alia/. Chirn. Acta. 36. 230 (1966). ( 5 ) H. T.”Hawkins, McClellan Central Labora’tory, “Volatilization of Gold During Carrier Free Dissolutions,” MCL-TM-71-74, 7 June 1971. 2398
Instrument Calibration. The spectrometers used in this work had been previously calibrated for 155Au using a standardized solution obtained from the United Kingdom Atomic Energy Authority using the sample preparation and analysis techniques described below. Dissolution Procedure. Aliquots of 195Au activity were added to samples of IPC paper or Whatman filter paper in 600-ml Teflon (Du Pont) beakers. Eash sample was dissolved in 200 ml of 90% fuming nitric acid with moderate warming. After the paper was in solution, the beakers were placed on a hot plate under maximum heat until the volume was reduced to approximately 50 ml. At this point the samples were cooled and 100 ml of fuming nitric acid and 30 ml of 70 % perchloric acid were added to each. Cuurion! Contact of perchloric acid with oxidizable or combustible materials may result in fire or explosion. Safety rules and additional references are listed in “Official Methods of Analysis” (6). Heating was resumed until the onset of a self-sustained “perchloric reaction” with the remaining organic material. After the perchloric reaction, the samples were treated with 20 ml HNO., and 20 ml HF and the mixture was reduced to perchloric fumes. Following dissolution of the sample in this fashion, the remaining solution (usually
