ANALYTICAL CHEMISTRY
674 CONCLUSION
LITERATURE CITED
The oxalate ion may be titrated by permanganate solution over extremely wide ranges of sulfuric acid concentration. The final concentration of the latter acid may be as much as 4 Af without introducing an appreciable error in the estimation of the oxalate ion.
(1) Fowler, R. M., and Bright, H. -4., J . Research Nat. Bur. Standurds, 15, 493 (1935). (2) Kolthoff,’I. M., and Sandell, E. B., “Textbook of Quantitative Inorganit Analysis,” p. 594, S e w York, Macmillan Co., 1943. RECEIVED for review October 24, 1952. Accepted February 5 , 1953.
Photometric Determination of Antimony in lead Using the Rhodamine B Method C . L. LUKE, Bell Telephone Laboratories, Inc., Murray Hill,.’V. J .
u order to determine traces of antimony in lead by the rhoda‘-mine B method ( 2 ) most of the lead must first be removed. The sulfate separation is satisfactory since the loss of antimony by occlusion is small enough to be ignored. Because of the high specificity of the rhodamine B test, further separations are not usually required. Milligram quantities of lead and a t least 100 micrograms of such metals as selenium, tellurium, bismuth, copper, zinc, iron, nickel, tin, and arsenic can be present. Low results for antimony are obtained unless it is reduced with sulfite just prior to the rhodamine B test. Apparently some catalytic oxidation occurs during solution of the antimony in sulfuric acid. hfter oxidation of the antimony with ceric sulfate it is essential that the rhodamine B be added as quickly as possible, since the antimony appears to be slowly converted into a nonreactive state. I n the present method the excess of oxidant is destroyed by adding an excess of rhodamine B. It has been reported ( 1 ) that gold and thallium give essentially the same color test as antimony; and that, when more than 100 micrograms of antimony are involved, a second benzene extraction is necessary to remove all the colored complex.
Table I.
Determination of -4ntimony in Various Samples of Lead Sample, Gram I 1
Samples Test Lead
1
1
1 I
+
+
+
14 14 16
1
NBS melting point lead
1 I 1
0 00005 o no005
1 Acid lead (0.1 Cu-0.02 Bi)
1
1 1
Lead (0.05 .4s-0.01 Ag)
0.:
0.3 Lead (0.07 As-0.05 Sn)
0.5 0.5
0 ?la 0.5b 0.5
Cerro de Paeco lead
Lead (0.15 As-0.1 Sn-0.1 Bi)
a
round,
4 8
1
PROCEDURE
Preparation of Calibration Curve. Tranbfer 0, 4,8, 12, and 16 ml. of standard antimony solution (1 microgram of antimony per ml.) to 125-ml. conical flasks. To prepare the standard antimony solution, dissolve pure antimony metal in hot sulfuric acid, aliquot, and dilute to volume with sulfuric acid (1 9). Add to each flask 5 grams of potassium bisulfate, enough sulfuric acid to make a total of 5 ml., and some silicon carbide crystals to aid in boiling. Dilute to 40 ml., add 15 ml. of hydrochloric acid, and then add 5 ml. of 6% sulfurous acid, Boil down to 40 ml., cool to room temperature, transfer to a 150-ml. Squihb tvpe separatory funnel, and dilute to 60 ml. Working quickly, add 1 ml. of ceric sulfate solution [0.5 gram of tetrasulfatoceric acid, H4Ce(S0J4, dissolved in 100 ml. of sulfuric acid (3 97)], mix, add 3 ml. of rhodamine B solution (0.2% aqueous solution), and mix. -4dd 15.0 ml. of benzene from a buret, shake vigorously for 1 minute, allow the layers to separate and then drain off and discard the aqueous layer. Shake once or twice, swirl, and allow to stand for 1 or 2 minutes until most of the suspended xater droplets have collected in the bottom of the funnel. Drain off and discard the accumulated aqueous layer. Drain the benzene layer through a fairly compact plug of fine-spun, chemically resistant glass wool to a clean dry 2-cm. absorption cell, and measure the transmittancy of the solution a t 565 mp using benzene as the reference solution. Prepare a calibration curve. Analysis of Sample. Dissolve 0.25 to 1.00 gram of the sample in a 125-mI. conical flask by heating with 5 grams of potassium bisulfate plus 6 ml. of sulfuric acid. Carry a reagent blank through the entire analysis. When solution is complete boil off all but 5 ml. of the sulfuric acid, cool, add 25 ml. of distilled water, swirl, add 5 ml. of hydrochloric acid, and heat just to boiling to dissolve any black resldue. Cool to room temperature, filter off the lead 99). Igsulfate, and wash once or twice with sulfuric acid (1 nore traces of peptized lead sulfate that may come through the paper. Add silicon carbide, 10 ml. of hydrochloric acid, and 5 ml. of 6% sulfurous acid, and dilute to 60 ml. Heat to boiling. Ignore the appearance of any colloidal selenium or tellurium. Boil the solution down to 40 ml., and proceed as directed for preparation of the calibration curve.
Antimony Found, 70 Added, y none 0 none 0
0
0 10 10
FI
12 13 17 0 0 9
10
10 0 0 in
n onni
0 5
0 5
n
0019
n
n n
0019 0019
0 0
0 0 0
0 3
n 4
*n
n 0 n
n 0001
0 0001
0 0016
0,2.5 0 2.5 0.25a 0 25b 0.25
0 0030 0 0030 o no29 0 on32
0.20 0.20 0.30a 0.20b 0.20
0.0055 0 0053
0 0052 0.0050
0 0
0 0 0 5 0 0 0
n 2
y
0 0 3 R
0 4
n n n 0 1
100 Micrograms of selenium added to the sample just before solution in
acid. b 100 Micrograms of tellurium added t o t h e sample just before solution in acid.
RESULTS
-4variety of lead samples, some of which contained added impurities, mere analyzed for antimony by the method. The results obtained are recorded in Table I in the column entitled Antimony Found, %. In order to test the accuracy of the method, the analyses were repeated after adding measured amounts of antimony, in the form of aliquot portions of a standard antimony sulfate solution (10 micrograms of antimony per ml.), to the metal samples before the solution in sulfuric acid. The results are recorded in Table I. The column entitled Antimony Found, y represents the weight of antimony found in the sample-antimony mivtures minus that in the metal sample. ACKNOWLEDGMEYT
The author rishes to thank Clarence Zischkau of the American Smelting and Refining Co., Barber, N. J., for calling attention to the necessity of adding the rhodamine B immediately after the ovidation with ceric sulfate. LITERATURE CITED
(1) Alford, W. C., private communication. (2) Maren, T.H., A N A L . CHEM.,19,487 (1947). RECEIVED for review October 17, 1952. Accepted December 24 1952.
