A: Triturate a quantity of powdered Tablets, equivalent to about 10 mg of thiamine hydrochloride, with 10 mL of 0.5 N sodium hydroxide, and filter. Using a 5-mL portion of the filtrate, proceed as directed in Identification test B under Thiamine Hydrochloride Injection, beginning with “then add 0.5 mL of potassium ferricyanide TS”: the specified reaction is observed.

B: Triturate a quantity of powdered Tablets, equivalent to about 10 mg of thiamine hydrochloride, with 10 mL of water, and filter: treated separately, 2-mL portions of the filtrate yield a red-brown precipitate with iodine TS and a white precipitate with mercuric chloride TS, and respond to the tests for Chloride 191.

C: To the remainder of the filtrate prepared for the preceding test add 1 mL of lead acetate TS and 1 mL of 2.5 N sodium hydroxide: a yellow color is produced. Heat the mixture for several minutes on a steam bath: the color changes to brown, and, on standing, a precipitate of lead sulfide separates.

Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C12H17ClN4OS·HCl dissolved, employing the procedure set forth in the Assay for niacin or niacinamide, pyridoxine hydrochloride, riboflavin, and thiamine under Water-Soluble Vitamins Tablets using filtered portions of the solution under test, suitably diluted with Dissolution Medium if necessary, in comparison with a Standard solution having a known concentration of USP Thiamine Hydrochloride RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C12H17ClN4OS·HCl is dissolved in 45 minutes.

(Official January 1, 2007)

Standard preparation— Prepare as directed for Standard Preparation under Thiamine Assay 531.

Assay preparation— Place not fewer than 20 Tablets in a flask of suitable size, half fill the flask with 0.2 N hydrochloric acid, and heat on a steam bath, with frequent agitation, until the tablets have dissolved or have disintegrated so that a uniform dispersion is obtained. Cool, transfer the contents of the flask to a volumetric flask, and dilute with 0.2 N hydrochloric acid to volume. If the mixture is not clear, either centrifuge it or filter it through paper known not to adsorb thiamine. Dilute a portion of the clear solution quantitatively and stepwise with 0.2 N hydrochloric acid to obtain a solution containing about 0.2 µg of thiamine hydrochloride per mL. Using this as the Assay Preparation, proceed as directed for Procedure under Thiamine Assay 531.