of Cr(V1) from CrB would likely vary with the stoichiometry of the sample used and therefore should be determined independently. Further, since the effect of experimental conditions such as current density, supporting electrolyte composition, and stirring rate on this empirical current efficiency is not known, this calibration procedure should be performed under conditions similar t o those t o be used in the subsequent titration. In addition t o the material studied in this report, chromium borides with the stoichiometries Cr2B, CrsBa,
Cr3B4, and CrB, have been reported ( I I ) . Evaluation of these materials as coulometric generants for Cr(V1) would be of interest. RECEIVED for review September 23, 1968. Accepted November 5,1968. B. Aronsson, T. Lundstriim, and s. Rundqvist, ,,Borides, Silicides, and Phosphides,” Methuen and Co., Ltd., London, 1965, p 12.
Determination of Silicon in Siloxane Polymers and Silicone-ContainingSamples Employing Alkali Fusion Decomposition Methods James H. Wetters and Robert C. Smith Dow Corning Corporation, Midland. Mich. 48640
THEUTILITY of direct sodium hydroxide fusions to decompose polymeric, solid siloxanes was recently described by Greive and Sporek ( I ) . Our laboratory has employed their techniques and new fusion decomposition procedures with both fluid and solid siloxane samples. Use of potassium hydroxide in place of sodium hydroxide in direct fusions was found t o give better recovery of silicon from siloxane polymers. The usefulness of the fusion methods was greatly extended by employing an alcoholic alkali pretreatment step in which siloxane bonds were converted to silanolates. This procedure reduced the loss of volatile siloxane materials and rearrangement products. Subsequent fusion of the sample after alcohol evaporation rernoved the alkyl or aryl groups from silicon, producing silicates suitable for spectrophotometric analysis using the reduced heteropoly blue complex method. EXPERIMENTAL Apparatus and Reagents. The Technicon AutoAnalyzer system for analysis of soluble silica in water ( 2 ) was modified as shown in Figure 1. All manual spectrophotometric analyses were performed using the Cary Model 14 spectrophotometer and 1- or 5-cm cells. Most decompositions were made in 75-ml nickel crucibles with covers (Fisher Scientific Co., 8-020). Saturated sodium butylate was prepared by dissolving 4.5 grams of sodium metal in 100 ml of reagent butyl alcohol using a Teflon-lined, stainless steel be-tker. After cooling, the solution was filtered through a 60-mesh stainless steel screen and stored in a polyethylene bottle. Direct Alkali Fusion Decomposition Procedure. Generally about 5 grams of sodium hydroxide or potassium hydroxide was placed in a nickel crucible, depending upon the nature and size of the sample. About 3 mg t o 20 grams of sample was then added. With siloxane polymers, 20 mg was optimilm for spectrophotometric analysis. The lid was placed on the crucible and heat applied gently at first using a Meker type burner to melt the alkali. The alkali was held in the molten state for two t o three minutes using a hot flame (1) W. H. Greive and K. F. Sporek, Winter Meeting, ACS, Phoenix,
Ariz., January 17-21, 1966, paper No. 43. (2) Technicon AutoAnalyzer Methodology, Silica, 111 F (water analyses), Technicon Corporation.
t o completely decompose the sample. After cooling the crucible to room temperature, the fusion mass was dissolved in 50 ml of water in a Teflon-lined, stainless steel beaker. Heat was gently applied t o speed the dissolution. The crucible was removed with tongs and rinsed with water. With biological samples, the solution was filtered while basic with No. 42 filter paper and a polyethylene funnel for removal of metal hydroxides. The fusionate was neutralized with hydrochloric acid to a pH near 1.5, then transferred to a 500or 1000-ml volumetric flask and diluted to volume. About 3 to 10 pg/ml of silicon in solution was.desired for analysis. Alcoholic Alkali Evaporation and Fusion Procedure. About 5 grams of alkali was added to the nickel crucible as above. With sodium hydroxide, 15 ml of isopropyl alcohol was added. When using potassium hydroxide, 1 to 10 ml of saturated sodium butylate solution was introduced. A sample of 3 mg to 20 grams was taken, and the mixture allowed t o set at room temperature for 30 minutes. The alcohol was slowly evaporated with the crucible on a hot plate a t low heat setting. Last traces of alcohol were removed with high heat setting. Fusion of the alkali, sample dissolution, and acidification were then carried out as described above. Analysis Procedures. Gravimetric and spectrophotometric methods were employed to evaluate recovery of silicon as reported in Table I. The 8-hydroxyquinoline (oxine) precipitation method was used essentially as described by McHard et al. (3). Sample aliquots were selected to give 0.05 to 0.3 gram of precipitate. Spectrophotometric analyses a t 815 mp of the reduced heteropoly blue complex were performed manually ( 4 ) and automatically ( 2 ) using a Technicon AutoAnalyzer assembly diagramed in Figure 1. Silicon concentrations of 0 to 15 pg/ml were rapidly analyzed using the latter system. RESULTS AND DISCUSSION
Typical silicon recovery data are given in Table I. Several linear and cyclic polydimethylsiloxanes and various other silicone materials were decomposed, and the resulting soluble (3) J. A. McHard, P. C. Servais, and H. A. Clark, ANAL.CHEM., 20, 325 (1948). (4) H. J. Horner, “Treatise on Analytical Chemistry,” Part 11, Vol. 12, Interscience, New York, N. Y., 1965, pp 287-8. VOL. 41, NO. 2, FEBRUARY 1969
379
TUBE SIZE,
IN. I.D.
r-i I
I
I PUMP
112 T COIL COLORIMETER
V DISCARD
Figure 1. Flow diagram of Technicon AutoAnalyzer assembly for 0 to 15 ppm silicon analysis silicate solutions analyzed by gravimetric or spectrophotometric methods. Generallv- immoved silicon recoverv was observed using potassium hydroxide rather than sodium hydroxide in direct fusions. Recoveries with low molecular weight linear and Cyclic PolYdimethYlsiloxanes were usually less than 50%, however. The use of an alcoholic alkali pretreatment step with either sodium or potassium hydroxide helped to minimize losses of volatile compounds and polymer rearrangement products. Siloxane bonds are converted to alkali metal silanolates in the gentle heating and alcohol evaporation step:
ssi--o--siE =SiOH
ROH
+ KOII
+ KOH
ROH
:=si
n
=Si-0-K
K + H o S ~(1)~
+ H20
After alcohol removal, fusion of the sample cleaved all organic groups from silicon-converting silanolate to water-soluble silicates. =Si-0-K
KOH fusion
+ hydrocarbons
K4Si04
Table I. Per Cent Recovery of Silicon
Sample Me3SiOSiMe3 Me3SiO(MezSiO)SiMe3 Me3SiO(Me2Si0)zSiMe3 Me3SiO(Me2Si0)&Me3 Me3SiO(Me2SiO)&Me3 Me3SiO(Me2SiOhSiMe3 Me3SiO(Me2SiO),SiMe3, lo00 cs. HO(MezSiO),OH gum (Me2SiO)3 (MezSi0)4 [(C&"la [(COH5 ) MeSiOl3 (MeViSiO), (ViSiO3/2)8 [(Ce")S103/~11z [(C6H6)Si03,218 (MeSiOyzh (CGHdSi(0Meh 710 Fluid 550 Fluid 705 Fluid 704 Fluid 702 Fluid (F8PrMeSiO)a Si metal Me3SiOH
380
ANALYTICAL CHEMISTRY
Direct alkali fusion KOH NaOH
Alcoholic-alkali evaporation and fusion BuOH IPA-NaOH NaOBu-KOH
... 1 ... 3 ...
...
26
85,'90
...
81 59
99,100 91 46
96 96 96 92
11 1 99 99 92 92 92 99 86 98 88 99 90 87 87 94 99
...
(2)
0 2
13
*..
6
*..
... *.. ... *.. 86
...
99 99
...
98 103 105
*.. 33
3 30 39 64 81
... ... 97
...
... ... 91 ... ...
31
45,77
...
88, 91
*..
96
100 99 98 97
... ... ...
...
... ... 99
...
99 98
91 92 92 99 98
101 98 103
*..
52
...
...
...
(3)
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
0
381
