A:Infrared Absorption á197Mñ—

B: The retention time of the clindamycin phosphate peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

Mobile phase— Dissolve 10.54g of monobasic potassium phosphate in 775mLof water,and adjust with phosphoric acid to a pHof 2.5.Add 225mLof acetonitrile,and mix.Pass through a filter having a 0.45-µm or finer porosity,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á625ñ).

pH2.5Buffer— Dissolve 10.54g of monobasic potassium phosphate in 1000mLof water,and adjust with phosphoric acid to a pHof 2.5.

Resolution solution— Prepare a solution in pH2.5Buffercontaining in each mLabout 0.24mg of USP Clindamycin Phosphate RSand about 6µg of USP Clindamycin Hydrochloride RS.

Standard preparation— Dissolve an accurately weighed quantity of USP Clindamycin Phosphate RSin pH2.5Bufferto obtain a solution having a known concentration of about 0.24mg per mL.

Assay preparation— Transfer one Vaginal Insert to a suitable 100-mLcontainer.Add 40mLof isooctane,and seal the container tightly with a teflon-lined septum and crimp cap.Shake vigorously for about 15minutes until all of the Vaginal Insert is dissolved.Add 40.0mLof pH2.5Buffer.Recap the container tightly,and shake vigorously for not less than 30minutes,taking care to avoid leakage.Allow the layers to separate,and remove a volume of the lower aqueous layer sufficient to perform the following steps.Pass the aqueous solution through a filter having a 5-µm or finer porosity,discarding the first 2mLof the filtrate.Collect the remaining filtrate,and dilute a portion quantitatively,and stepwise if necessary,with pH2.5Bufferto obtain a solution containing the equivalent of about 0.2mg of clindamycin (C18H33ClN2O5S)per mL,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm ×25-cm column that contains packing L7.The flow rate is about 1mLper minute.Chromatograph the Resolution solutionas directed for Procedure.The resolution,R,between clindamycin phosphate and clindamycin hydrochloride is not less than 2.0,when calculated by the formula: in whicht2is the retention time,in minutes,of clindamycin hydrochloride;t1is the retention time,in minutes,of clindamycin phosphate;whlis the width,in minutes,of the clindamyicn phosphate peak at half-height;and wh2is the width,in minutes,of the clindamyicn hydrochloride peak at half-height.Chromatograph the Standard preparationas directed for Procedure:the relative standard deviation for replicate injections is not more than 2.5%.

Procedure— Separately inject equal volumes (about 35µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the major peak responses.Calculate the quantity,in mg,of clindamycin (C18H33ClN2O5S)equivalent in the Vaginal Insert taken by the formula: in which Cis the concentration,in mg per mL,of USP Clindamycin Phosphate RSin the Standard preparation;Pis the potency,in µg,of clindamycin (C18H33ClN2O5S)per mg,of USP Clindamycin Phosphate RS;Lis the labeled quantity,in mg,of clindamycin (C18H33ClN2O5S)equivalent in the Vaginal Insert;Dis the concentration,in mg per mL,of clindamycin equivalent in the Assay preparation,based on the labeled quantity in the Vaginal Insert and the extent of dilution;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.Use as the Assayvalue the average of the determinations obtained for Content Uniformity in the test for Uniformity of dosage units.