A general improvement in recovery of silicon over that obtained using direct alkali fusion is noted in Table I. Improved retention of silicon from the cyclic polydimethylsiloxanes was particularly noteworthy. Because the major products from rearrangement of polydimethylsiloxanes are these cyclic species, it might be expected that results would markedly improve with all linear polymers. However, the silicon from linear polydimethylsiloxanes with molecular weights and boiling points below that of octamethylpentasiloxane (molecular weight 385, boiling point 230 "C) was not held sufficiently for quantitative use. Decomposition of phenyl-containing silicones generally gave recoveries of 90% or better with both the direct fusion
and alcoholic alkali modified methods. Significant improvements were obtained with the latter method as shown in Table I. A variety of inorganic and organic samples were analyzed for silicon using these decomposition methods and spectrophotometric analysis. Typical applications were the analysis of silicon in silicon metal, cement, solid silicones, silicone emulsions, solvents, organic oils, silicone treatments (paper, fabric, leather), and biological samples (fluids, tissues). RECEIVED for review October 28, 1968. Accepted November 7, 1968. Presented at the 16th Detroit Anachem Conference, September 26,1968.
Quantitative Electrodeposition of Actinides from Dimethylsulfoxide Thomas H. Handley and J. H. Cooper Analytical Chemistry Dicision, Oak Ridge National Laboratory, P. 0. Box X , Oak Ridge, Tenn. 37831
A SIMPLE, quantitative, and fast technique for preparing sources for analytical alpha spectrometry by electrodeposition from dimethylsulfoxide was developed. In the presence of fluoride ion, sexivalent americium was preferentially electrodeposited with respect to the trivalent curium ion. A decontamination factor of several hundred was obtained. Thin uniform sources are required for precise, accurate, and quantitative alpha spectrometry. For application to routine analytical use any method of source preparation must also be simple, fast, reproducible, and inexpensive. The method generally wed-that of direct evaporation-is simple, fast and quantitative, but often fails because of loss of energy resolution caused by solids pile up, and variation of geometric factors. Other methods of source preparation-such as hot not filament sublimation ( I ) and electrospraying (2)-are readily adaptable to a service laboratory. Some experimenters have successfully electrodeposited sources from aqueous solutions low in acid, but this method has not lent itself to routine use in our laboratories. Others have used organics such as alcohol (3), but deposition time is long and there is a potential fire hazard. The dipolar aprotic solvent dimethylsulfoxide, DMSO, solvates many inorganic salts and is miscible with water and many organics. DMSO is potentially useful as a deposition solvent for both aqueous and organic solutions of actinides. DMSO is relatively nonconducting; however, with traces of water and acids currents are obtained that permit quantitative deposition of tracer actinides in a reasonably short time. EXPERIMENTAL
Plating Cell. Any number of plating cell designs would be quite adequate. Simplicity and ease of cleaning anddisassembly are the key words in any cell design. Any regulated power supply capable of delivering up to 400 V and 100 mA will be suitable. Reagents. A technical bulletin by the Crown Zellerbach Corp., Camas, Wash., describes dimethylsulfoxide, DMSO, (1) N. Jackson, J . Sci. Instrum., 37, 169 (1960). (2) P. S. Robinson, Nucl. Instrum. Methods, 40, 136 (1966). (3) Stephan M. Kim, John E. Noakes, L. K. Akers, and W. W. Miller, ORINS Report 48, Dec. 15, 1965.
as a water-white, colorless, water-miscible hydroscopic liquid, boiling point 189 "C; conductivity at 20 "C is 3 X (ohm-' cm-l). DMSO is relatively inexpensive and readily available from several chemical supply houses. It is reported that DMSO migrates rapidly through the skin and may carry dissolved materials ( 4 ) . Therefore, a series of tests was conducted to determine the rate of migration of tracer americium-241 and/or curium-244 through rubber gloves used in our laboratory. During a 20-hour exposure of a glove, negligible migration was found. However, contact with the skin by DMSO solutions should be avoided, and in the event contact is made, immediate washing with water is recommended. Procedure. An aliquot of the sample to be analyzed was added to a deposition cell that contained -4 ml of DMSO. The anode should be 3 to 4 mm above the cathode. A constant current of 15 mA/cm2 was applied for 10 minutes. No stirring was necessary when preparing sources up to 1 cm in diameter; convection currents created by the current heating of the DMSO were adequate for mixing. When preparing sources >1 cm in diameter, a rotating platinum disk anode was used. Tests showed 5 minutes to be adequate for quantitative deposition; however, a deposition time of 10 minutes was routinely used. At the end of deposition the DMSO was removed by aspiration and the cell was disassembled. The source plate was washed with a spray of chloroform and then acetone to remove excess DMSO. Although deposition was quantitative, the chimney and platinum anode were usually cleaned between successive depositions. During deposition the DMSO became warm and conductivity increased; if the current was allowed to go too high the DMSO boiled; however, deposition was still quantitative. RESULTS AND DISCUSSION
Deposition Time and Current Density. A study of americium-241 deposition as a function of time at 15 mA/ cm2 clearly showed that a 5-minute deposition time is adequate; however, in practice most deposition times were 10 minutes. Studies also showed that a current density of 15 mA/cm2 is necessary for quantitative deposition. A test of reproducibility showed that successive plates prepared from the same stock solution agreed within *l%. A (4) Alan Buckley, J. Chem. Educ., 42, 674 (1965). VOL. 41, NO. 2, FEBRUARY 1969
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Figure 1. Selective electrodeposition of Ams+ Sample CFD-16 Source distance, 4.0 cm Source size, 10.2 cm Detector, 2.3 cm2
negligible amount of activity was found in the DMSO and on cell components after deposition. Ignition of Sources. Most analysts ignite sources t o remove volatile deposits, with corresponding improvement in resolution and adherence to the backing plate. For sources prepared by deposition from DMSO, ignition did not improve resolution. Furthermore, the radioactive tracer adhered strongly to the plate without ignition. Rubbing briskly with a tissue removed, on the average, only 1 or 2%. DMSO as a Diluent. Dilutions of 152-4E~, I44Ce, *41Am, or *44Cm in DMSO stored in a volumetric flask were found to be stable for two months, at which time the test was discontinued. These dilutions were very low in mineral acid,
