Edition: BP 2025 (Ph. Eur. 11.6 update)
Action and use
Used, with Alpha Tocopheryl Acetate, in the treatment of nutritional muscular dystrophy.
DEFINITION
Potassium Selenate contains not less than 97.0% and not more than 100.5% of K2SeO4, calculated with reference to the dried substance.
CHARACTERISTICS
Colourless crystals or a white, crystalline powder. Freely soluble in water.
IDENTIFICATION
A. Yields the reactions characteristic of potassium salts, Appendix VI.
B. To a solution of 0.1 g in 3 mL of water add 1 mL of hydrochloric acid and 0.5 mL of hydrazine hydrate and boil. A red precipitate is produced.
C. Acidify 1 mL of a 1% w/v solution with 2M hydrochloric acid and add 0.15 mL of barium chloride solution. Wash the precipitate with water and boil with hydrochloric acid. Chlorine is evolved.
TESTS
Chloride
0.3 g complies with the limit test for chlorides, Appendix VII (170 ppm).
Selenite
Not more than 0.1%, calculated as SeO3, when determined by the following method. Dissolve 2.0 g in 50 mL of water, add 50 mL of 9M sulfuric acid, 12 g of disodium hydrogen orthophosphate and 10 mL of 0.02M potassium permanganate VS and allow to stand for 20 minutes with occasional agitation. Titrate the excess of potassium permanganate with 0.1M ammonium iron(II) sulfate VS. Each mL of 0.02M potassium permanganate VS is equivalent to 6.348 mg of SeO3.
Loss on drying
When dried to constant weight at 105°, loses not more than 0.1% of its weight. Use 1 g.
ASSAY
Dissolve 1 g in 60 mL of water, add 15 mL of hydrochloric acid and 5 mL of a 50% w/v solution of hydrazine hydrate, boil, heat on a water bath for 3 hours, and allow to stand overnight. Transfer the precipitated selenium to a weighed, sintered- glass crucible, wash with hot water until the washings are free from chloride ions, rinse with absolute ethanol and dry at 105° to constant weight. Correct for the amount of selenium present as selenite found in the test for selenite. Each mg of selenium is equivalent to 2.801 mg of K2SeO4.
