Selenium Sulfide USP Grade

SeS2 143.09 -- [7488-56-4].
Selenium Sulfide contains not less than 52.0 percent and not more than 55.5 percent of selenium (Se).

Identification:
A: Filter 20 mL of the solution of Selenium Sulfide prepared as directed in the Assay, and to 10 mL of the filtrate add 5 mL of water and 5 g of urea. Heat to boiling, cool, and add 2 mL of potassium iodide solution (1 in 10): a yellowish orange to orange color is produced, and it darkens rapidly (presence of selenium).
B: Allow the solution obtained in Identification test A to stand for 10 minutes, filter, and to the filtrate add 10 mL of barium chloride: the solution becomes turbid (presence of sulfur).

Tests:
Residue on ignition: not more than 0.2%.
Soluble selenium compounds:
Test solution: Mix 10.0 g of Selenium Sulfide with 100.0 mL of water in a 250-mL flask, allow to stand for 1 hour, with frequent agitation, and filter. To 10.0 mL of the filtrate add 2 mL of 2.5 M formic acid, dilute with water to 50 mL, mix, and adjust, if necessary, to a pH of 2.5 ± 0.5. Add 2 mL of freshly prepared 3,3-diaminobenzidine hydrochloride solution (1 in 200), mix, allow to stand for 45 minutes, and adjust with 6 N ammonium hydroxide to a pH of 6.5 ± 0.5. Transfer to a separator, add 10.0 mL of toluene, shake vigorously for 1 minute, allow the layers to separate, and discard the aqueous phase.
Standard solution: Using 10.0 mL of a solution of selenious acid containing 0.5 :g of selenium per mL, prepare a solution as directed under Test solution, beginning with “add 2 mL of 2.5 M formic acid.”
Procedure: Concomitantly determine the absorbances of the toluene layers of the Test solution and the Standard solution in 1-cm cells at 420 nm, with a suitable spectrophotometer, using a blank consisting of the same quantities of the same reagents treated in the same manner as the Test solution: the absorbance of the Test solution is not greater than that of the Standard solution (5 ppm).
Assay: Place about 100 mg of Selenium Sulfide, accurately weighed, in a suitable container, add 25 mL of fuming nitric acid, and digest over gentle heat until no further solution occurs. Cool, transfer the solution to a 250-mL volumetric flask containing 100 mL of water, cool again, dilute with water to volume, and mix. Pipet 50 mL of the solution into a suitable flask, add 25 mL of water and 10 g of urea, and heat to boiling. Cool, add 3 mL of starch TS, then add 10 mL of potassium iodide solution (1 in 10), and immediately titrate with 0.05 N sodium thiosulfate VS. Perform a blank determination, and make any necessary correction. Each mL of 0.05 N sodium thiosulfate is equivalent to 987.0 microgm of Se.