Methyl orange solution—
Transfer 15.5 g of boric acid and 2.0 g of methyl orange to a glass-stoppered, 1000-mL flask. Add 500 mL of water, insert the stopper, and shake by mechanical means for not less than 3 hours. Filter through retentive filter paper, and wash the filtrate with two 100-mL portions of chloroform, discarding the chloroform washings. Store the
Methyl orange solution over 50 mL of chloroform in a glass-stoppered bottle.
Procedure—
Prepare a
Test preparation by passing a 60-mL portion of the dissolution solution through a suitable filter, discarding the first 5 mL of the filtrate, and diluting the subsequent filtrate quantitatively, if necessary, to obtain a concentration of about 1 µg of thiothixene per mL. Prepare a
Standard preparation of
USP Thiothixene RS in
Dissolution Medium having a known concentration of about 1 µg per mL. Transfer 40.0 mL each of the
Test preparation, the
Standard preparation, and
Dissolution Medium to provide the blank, to individual separators, each containing 8.0 mL of
Buffer solution, 10.0 mL of
Methyl orange solution, and 50.0 mL of chloroform. Shake for 3 minutes, allow the layers to separate, transfer 40.0 mL of the chloroform layer, clarified by centrifugation, to a 60-mL separator containing 8.0 mL of dilute hydrochloric acid (1 in 120), shake for 1 minute, and allow the layers to separate. Concomitantly determine the absorbances of the aqueous layers in 1-cm cells, at the wavelength of maximum absorbance at about 508 nm, with a suitable spectrophotometer, using the blank to set the instrument. Calculate the quantity, in µg per mL, of C
23H
29N
3O
2S
2 in the
Test preparation taken by the formula:
C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Thiothixene RS in the
Standard preparation, and
AU and
AS are the absorbances of the solutions from the
Test preparation and the
Standard preparation, respectively, and, from the known extent of dilution, determine the amount of it in the dissolution solution.
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of ethyl acetate, methanol, and diethylamine (65:35:5) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and locate the spots on the plate by viewing under short- and long-wavelength UV light. Spray the plate lightly with acidified iodoplatinate spray reagent (prepared by mixing 1 volume of hydrochloric acid with 50 volumes of potassium iodoplatinate TS): the RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution and the mixed test-Standard solution.