Mobile phase, Potassium phosphate buffer, Sodium glycocholate solution, Reference solution, Standard solution, System suitability solution, and Chromatographic system— Proceed as directed in the test for Exchange capacity under Cholestyramine Resin.

Test solution— Transfer an accurately weighed portion of Cholestyramine for Oral Suspension, equivalent to about 100 mg of cholestyramine resin, to a 25-mL conical flask. Pipet 15.0 mL of Sodium glycocholate solution into the flask, and stir by mechanical means for 2 hours. Transfer the contents to a centrifuge tube, and centrifuge for 15 minutes. Transfer 5.0 mL of the supernatant to a 50-mL volumetric flask, and dilute with water to volume.

Procedure— Separately inject equal volumes (about 50 µL) of the Reference solution, the Standard solution, and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of cholestyramine resin per mg of Cholestyramine for Oral Suspension taken by the formula: in which M is the stated value, in mg, of sodium glycocholate absorbed per g of USP Cholestyramine Resin RS; rR, rU, and rS are the peak responses obtained from the Reference solution, the Test solution, and the Standard solution, respectively; WS is the weight, in mg, of USP Cholestyramine Resin RS taken to prepare the Standard solution; WU is the weight, in mg, of Cholestyramine for Oral Suspension taken to prepare the Test solution; and Q is the quantity of sodium glycocholate absorbed per g of dried cholestyramine resin, as obtained in the test for Exchange capacity under Cholestyramine Resin.