A: Place a quantity of Oral Suspension, equivalent to about 100 mg of sulfamethoxazole, in a 50-mL centrifuge tube; add 5 mL of ammonium hydroxide; and shake gently. Add 25 mL of methanol, shake thoroughly for 3 minutes, centrifuge, decant the supernatant into a 50-mL volumetric flask, dilute with methanol to volume, and mix. Apply 50 µL of this solution and 50 µL of a solution prepared by dissolving 100 mg of USP Sulfamethoxazole RS in 5 mL of ammonium hydroxide and diluting with methanol to 50.0 mL to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of alcohol, n-heptane, chloroform, and glacial acetic acid (25:25:25:7) 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 allow the solvent to evaporate. Locate the spots on the plate by lightly spraying with a solution prepared by dissolving 0.10 g of p-dimethylaminobenzaldehyde in 1 mL of hydrochloric acid and diluting with alcohol to 100 mL: the RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

B: Transfer a quantity of Oral Suspension, equivalent to about 500 mg of sulfamethoxazole, to a 50-mL centrifuge tube; add about 25 mL of water; mix; and centrifuge. Decant and discard the supernatant, resuspend the residue in 25 mL of water, mix, and centrifuge again. Decant and discard the clear supernatant. Repeat the washing procedure an additional two times. Dissolve the residue in 10 mL of hydrochloric acid, and add 15 mL of sodium nitrite solution (1 in 100) and 5 mL of sodium hydroxide solution (1 in 10) containing 10 mg of 2-naphthol: a red-orange precipitate is produced.

FOR ORAL SUSPENSION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.

FOR ORAL SUSPENSION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.

(Official January 1, 2007)