A:Infrared Absorption á197Mñ.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,both relative to the internal standard,as obtained in the Assay.

Mobile phase— Prepare a filtered and degassed mixture of 0.01Msodium 1-pentanesulfonate,methanol,and glacial acetic acid (80:20:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Transfer about 50mg of hydrochlorothiazide to a 25-mLvolumetric flask,add methanol to volume,and mix.

Standard preparation— Dissolve an accurately weighed quantity of USP Diazoxide RSin methanol,and dilute quantitatively,and stepwise if necessary,with methanol to obtain a solution having a known concentration of about 1mg per mL.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,add 2.0mLof Internal standard solution,dilute with a mixture of water and methanol (4:1)to volume,and mix to obtain a solution having a known concentration of about 50µg of USP Diazoxide RSper mL.

Assay preparation— Transfer about 50mg of Diazoxide,accurately weighed,to a 50-mLvolumetric flask,add methanol to volume,and mix.Transfer 5.0mLof this solution to a 100-mLvolumetric flask,add 2.0mLof Internal standard solution,dilute with a mixture of water and methanol (4:1)to volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm ×30-cm column that contains packing L11.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the resolution,R,between the analyte and internal standard peaks is not less than 5;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.The relative retention times are about 0.4for hydrochlorothiazide and 1.0for diazoxide.Calculate the quantity,in mg,of C8H7ClN2O2Sin the portion of Diazoxide taken by the formula: in which Cis the concentration,in µg per mL,of USP Diazoxide RSin the Standard preparation;and RUand RSare the peak response ratios obtained from the Assay preparationand the Standard preparation,respectively.