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V O L U M E 2 5 , NO. 2, F E B R U A R Y 1 9 5 3 potassium iodide to which no thallium was added. This activity is subtracted from the observed counting rates of the other samples to give the net counting rates due to the added thallium shown in column 4. The average specific activity from the data in column 4 is 668 3~ 24 counts per minute per microgram of thallium in the sample. The data show that the counting rate is proportional to the amount of thallium added within esperimental error. The thallium content of an unknown sample is obtained by use of either a standard curve or the specific activit?. value given abow.
served was less than that espected for 0.1 p.p.m. of thallium in the zinc. illuminum absorption measurements were made on all samples as a check on the purity of the observed radioactivity. The range of the beta radiation was found to be 280 mg. per sq. em. (corresponding to 0.75 m.e.v.), in agreement with the known energy of T1204. In addition, the counting rates of all samples n’ere found to be constant over a period of 2 weeks, showing the absence of short-lived contaminants. DISCUSSION
Table I.
Counting Rates of Standard Thallium Samples Observed
TI Added, Sample
Y
1 2 3 4
0 1.23 12.3 123
Activity T1 Due t o Activity .4dded T’ Counts per .AxinUte 218 997 8,668 84.418
...
778 8,450 B4,200
The counting rate of sample 1 corresponds to 0.33 microgram or 0.33 p.p.m. of thallium in the pure potassium iodide. At this low concentration spectrophotometric measurements on single crystals of the pure potassium iodide are not sufficiently sensitive to determine the thallium content, as only a trace of the characteristic absorption bands of thallium ( 2 ) was observed. A sample of Merck reagent grade potassium iodide was also analyzed for thallium impurity. In this case, holvever, an activity barely detectable above the background of the counter was observed, corresponding to an upper limit of about 0.01 p.p.m. -4s a test of the application of the method to materials other than potassium iodide, a 1-gram sample of pure zinc (reagent, Baker and Adamson) Tas analyzed for thallium impurity. [It is reported (3) that zinc often contains traces of thallium.] ,4slight activity (approyimately equal to the background of the counter) was observed. The energy of the beta radiation as determined by absorption, however, was about 2 ni.e.v., which is not characteristic of T 1 2 0 4 , and the activity ob-
The data of Table I shoTT that with an exposure to a flux of 2 x 1012 neutrons per sq. em. per second for 3 days in the Argonne reactor, 1microgram of thallium gives rise to about 670 counts per minute of T1204. Since the background of the counter is about 20 counts per minute, the indicated sensitivity of the radioactivation method under these conditions is about 0.1 microgram of thallium. The sensitivity can be increased further by lengthening the time of irradiation. From the data obtained in this work it is estimated that the method is accurate to about 5% down to a t least the l-microgram level. I n order to check the accuracy of the method, two similar sets of samples (one standard and two unknowns) were given separate neutron irradiations and analyzed for thallium. The data obtained on the unknowns agreed to within 5%. LITERATURE CITED (1) Boyd, G. E., A N . ~ LCHEM., . 21, 336 (1949). (2) Hilsch, R., P h y s . Z . , 38, 1031 (1937). (3) Hopkins, B. S.,“Chapters in the Chemistry of the Less Familiar
Elements,” Champaign, Ill., Stipes Publishing Co., 1939. (4) Lundell, G. E. F., and Hoffman, J. I., “Outlines of Methods of Chemical Analysis,” New York, John Wiley 8- Sons, 1938. ( 5 ) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., New York, Interscience Publishers, 1950. (6) Seaborg, G. T., and Perlman, I., Rers. Modern Phys., 20, S o . 4, 585 11948). (7) Yuster, P. H., and Delbecq. C. J., J . Chem. Phys. (to be published). RECEIVED for review July 10, 1952.
Accepted October 13, 1952.
Separation of Antimony by Solvent Extraction CHARLES E. WHITE AND HARRY J. ROSE‘ University of Maryland, College Park, M d .
l H E difficulty of separating antimony from tin and arsenic for the quantitative determination of antimony is well known. The extraction of the antimony-rhodamine B complex with benzene ( 1 ) is a long established procedure and recently West and Hamilton (3)have shown that the antimony iodide complex can be extracted with benzene. I n order to find a more suitwble method for the separation of antimony from other similar elements, a study was initiated in which various complexing agents were used in conjunction with extracting solvents. REAGENTS
Intimony Solution. iintimony trichloride solution in 8 ,V hydrochloric acid about 1 gram per liter standardized with iodine. Dilute to 10 mg. per liter in 8 N hydrochloric acid. Rhodamine B, 0.2% aqueous solution. Ceric sulfate, 0.1 N ceric sulfate in 2 N sulfuric acid. Hydroxylamine hvdrochloride, 0.1 % aqueous solution. Benzene, oxalic acid, citric acid, 85% phosphoric acid; reagent grade. Ethyl acetate, reagent grade, redistilled. 1
Present address, C.S. Geologiral S u r i e y , Washington 26, D. C.
EXPERIRZ ENTA L
The following complesing agents were tried: tartaric acid, citric acid, oxalic acid, dibenzoyl methane, acetylacetone, catechol and resorcinol. Extracting solvents employed were: methyl acetate, ethyl acetate, butyl acetate, acetoacetic ester, acetylacetone, ethyl acrylate, chloroform, and carbon tetrachloride. Preliminary tests were conducted with combinations of the complexing agents and the various solvents. Both trivalent and pentavalent antimony salts were used and the residual antimony was estimated by sulfide precipitation or by rhodamine B. The results of a series of experiments showed that oxalic acid and citric acid were both good complexing agents for extraction purposes and that a mixture of these tlvo was better than either used separately. Pentavalent antimony seemed to extract slightly easier than the trivalent with these reagents. The increasing orders of extraction with the other complexing agents used were as follows: dibenzoyl methane, catechol, resorcinol, acetylacetone, tartaric acid, osalic acid, citric acid. Ethyl acetate proved to be the best of the extracting liquids for the citrate-oxalate complex. Methyl acetate was too soluble in water for use as an extracting agent. The increasing order
352
ANALYTICAL CHEMISTRY
of efficiency of the remaining solvents was: butyl acetate, acetoacetic ester, acetylacetone, ethyl acrylate, chloroform, carbon tetrachloride, ethyl acetate. Elements which were considered to be of some interest in connection with the analysis for antimony and those which interfere in the rhodamine B determination R-ere tested for extraction from the osalate-citrate mixture by ethyl acetate. I n each case similar conditions to those described for antimonj- were employed. In order to determine if a metallic ion was extracted, the ethyl acetate estract was evaporated to dryness and the residue dissolved in hydrochloric acid. In all cases the ions were a t their higher states of oxidation, since, in t,he procedure developed, ceric sulfate was used to oxidize the antimony before extraction. Hydrogen sulfide was used to test for the ions with the exception of those of iron and tungsten. Iron was detected with potassium thiocyanate and the zinc reduction test was used for tungsten. Iron, tin, copper, cadmium, lead, germanium, and tellurium werc not extracted. drsenic, bismuth, and molybdenum n-ere estracted in trace amounts. Silver and mercury were extracted in moderate quantities and gold was almost completely extracted. Because mercury and gold interfere with the rhodamine B procedure, these elements if present must be removed by other methods. In order to find the effect of acidity on the extraction, a series of experiments was conducted where the hydrochloric acid concentration of the antimony solution was varied from 0.5 S to 6 S. These results are indicated in Table I. In these experiments 25 mi. of the acid solution contained 50 micrograms of antimony, 10 mg. of oxalic acid, and 10 mg. of citric acid. This mixture was shaken in a separatory funnel with 25 ml. of ethyl acetate and the residual antimony was determined in the aqueous layer by the rhodamine B method. The rhodamine B solution was compared to a standard in a Pulfrich photometer using the 565-mp filter. The results indicated that t,he hydrochloric acid concentration should be in the vicinity of 1 to 2 S to give the best initial extract,ion. The distribution ratio of the extracted antimony(T') to the residual was calculated to be 5.03. The corresponding ratio for the antimony(II1) was found to be 4.33; therefore in all subsequent determinations the antimony was oxidized to :I valence of 5 beforc extracting with ethyl acetate. The distrihution ratio was confirmed by estracting IO-, 20-, 30-, 40-, 50-, and 60nil. portions of the aqueous solution with equal volumes of ethyl acetate. It is obvious that three extractions with ethyl acetate will reduce the pentavalent ant,imony in the aqueous layer to less than 0.5% of the original. PROCEDURE FOR ANALYSIS OF ALLOYS
Three Xational Bureau of Standard samples were analyzed in order t o test the accuracy of the method, using only the extraction method for the separation of antimony from other elements. The compositions of the analyzed samples were as follows: No. 124, Cu 83.77, Zn 5.46, P b 4.78, Sn 4.69, Ki 0.45, Fe 0.38: Sb 0.23, Si 0.075, S 0.071, P 0.037, AI 0.016%; S o . 62B, Cu 57.39, Zn 37.97, Mn 1.29, A1 0.97, Sn 0.96, Fe 0.82, P b 0.28, .Xi 0.27, Si 0.048, Sb 0.005, As 0.004, Ag 0.005%; S o . 108, zinc spelter containing P b 0.47, Cd 0.92, Fe 0.31, Cu 0.0004, Sn 0.0008, As 0.0001, Sb 0.0003, Ge 0.0001, Ga 0.0003, hIn 0.002, Ag
