Mobile phase— Add 10 mL of glacial acetic acid to 750 mL of methanol in a 1000-mL volumetric flask, dilute with water to volume, mix, and pass through a membrane filter.

System suitability solution— Dissolve accurately weighed quantities of USP Gemfibrozil RS, USP Gemfibrozil Related Compound A RS, and 2,5-dimethylphenol in Mobile phase to obtain a solution having known concentrations of about 0.2 mg per mL, 0.05 mg per mL, and 0.05 mg per mL, respectively.

Standard solution— Transfer 10 mg each of USP Gemfibrozil RS and USP Gemfibrozil Related Compound A RS, both accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with methanol to volume, and mix. Transfer 5.0 mL of this solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Test solution— Transfer about 100 mg of Gemfibrozil, accurately weighed, to a 10-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 276-nm detector and a 4.0-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.35 for 2,5-dimethylphenol, 1.0 for gemfibrozil, and 2.1 for gemfibrozil related compound A; and the relative standard deviation for replicate injections is not more than 3.0%.

Procedure— Separately inject equal volumes (about 100 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms for at least three times the retention time of gemfibrozil, and measure the areas for the major peaks. Calculate the percentage of gemfibrozil related compound A in the portion of Gemfibrozil taken by the formula: in which C is the concentration, in mg per mL, of USP Gemfibrozil Related Compound A RS in the Standard solution; W is the weight, in mg, of Gemfibrozil taken to prepare the Test solution; and rU and rS are the peak areas for gemfibrozil related compound A obtained from the Test solution and the Standard solution, respectively: not more than 0.1% of gemfibrozil related compound A is found. Calculate the percentage of any other impurity in the portion of Gemfibrozil taken by the formula: in which CG is the concentration, in mg per mL, of USP Gemfibrozil RS in the Standard solution; ri is the peak area of each individual impurity obtained from the Test solution; rG is the gemfibrozil peak area obtained from the Standard solution; and W is as defined above: not more than 0.1% of any other impurity is found; and not more than 0.5% of total impurities is found.

Mobile phase— Add 10 mL of glacial acetic acid to 800 mL of methanol in a 1000-mL volumetric flask, dilute with water to volume, mix, and pass through a membrane filter.

Standard preparation— Dissolve a suitable quantity of USP Gemfibrozil RS, accurately weighed, in methanol to obtain a solution having a known concentration of about 1 mg per mL. Transfer 5.0 mL of this solution to a 25.0-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Assay preparation— Transfer about 100 mg of Gemfibrozil, accurately weighed, to a 100-mL volumetric flask, dissolve in and dilute with methanol to volume, and mix. Transfer 5.0 mL of this solution to a 25.0-mL volumetric flask, dilute with Mobile phase to volume, and mix.

System suitability preparation— Prepare a solution in Mobile phase containing, in each mL, about 0.2 mg of gemfibrozil and about 0.05 mg of 2,5-xylenol.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 276-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 0.8 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.0%. Chromatograph about 10 µL of the System suitability preparation: the resolution, R, between gemfibrozil and 2,5-xylenol is not less than 8.0.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph by means of a suitable microsyringe or sampling valve, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C15H22O3 in the portion of Gemfibrozil taken by the formula: in which C is the concentration, in mg per mL, of USP Gemfibrozil RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.