Mobile phase , Resolution solution, Standard preparation, and Chromatographic system—Proceed as directed in the Assay under Clindamycin Phosphate Gel.

Assay preparation— Transfer an accurately weighed quantity of Cream, equivalent to about 20 mg of clindamycin (C18H33ClN2O5S), to a 125-mL conical flask, add 100.0 mL of Mobile phase and about 10 glass beads (about 10 mm in diameter). Insert the stopper in the flask securely, and shake by mechanical means at 50 for about 1 hour. Cool in an ice bath for about 20 minutes, and centrifuge. Filter a few mL of the cloudy lower layer through a filter of 2 µm or finer porosity, and use the filtrate as the Assay preparation.

Procedure— Proceed as directed for Procedure in the Assay under Clindamycin Phosphate Gel. Calculate the quantity, in mg, of clindamycin (C18H33ClN2O5S) in the portion of Cream taken by the formula: in which the terms are as defined therein.