Mobile phase— Add 10mLof glacial acetic acid to 750mLof methanol in a 1000-mLvolumetric 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 phaseto obtain a solution having known concentrations of about 0.2mg per mL,0.05mg per mL,and 0.05mg per mL,respectively.

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

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

Chromatographic system (see Chromatography á621ñ)— 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 1mLper minute.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.35for 2,5-dimethylphenol,1.0for gemfibrozil,and 2.1for gemfibrozil related compound A;and the relative standard deviation for replicate injections is not more than 3.0%.

Procedure— Separately inject equal volumes (about 100µL)of the Standard solutionand the Test solutioninto 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 Ain the portion of Gemfibrozil taken by the formula: in which Cis the concentration,in mg per mL,of USP Gemfibrozil Related Compound A RSin the Standard solution;Wis the weight,in mg,of Gemfibrozil taken to prepare the Test solution;and rUand rSare the peak areas for gemfibrozil related compound Aobtained from the Test solutionand the Standard solution,respectively:not more than 0.1%of gemfibrozil related compound Ais found.Calculate the percentage of any other impurity in the portion of Gemfibrozil taken by the formula: in which CGis the concentration,in mg per mL,of USP Gemfibrozil RSin the Standard solution;riis the peak area of each individual impurity obtained from the Test solution;rGis the gemfibrozil peak area obtained from the Standard solution;and Wis 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.

Solvent— Use dimethyl sulfoxide.

Mobile phase— Add 10mLof glacial acetic acid to 800mLof methanol in a 1000-mLvolumetric 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 1mg per mL.Transfer 5.0mLof this solution to a 25.0-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

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

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

Chromatographic system(see Chromatography á621ñ)— 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 0.8mLper 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 10µLof 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 10µL)of the Standard preparationand the Assay preparationinto 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 C15H22O3in the portion of Gemfibrozil taken by the formula: in which Cis the concentration,in mg per mL,of USP Gemfibrozil RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.