Mobile phase— Prepare a filtered and degassed mixture containing 6volumes of acetonitrile and 4volumes of 0.01Mdibasic potassium phosphate,and adjust by the addition of dilute phosphoric acid (1in 10)to a pHof 7.8±0.1.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution of benzophenone in methanol containing about 0.5mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Azaperone RSin methanol,and dilute quantitatively with methanol to obtain a solution having a known concentration of about 0.5mg per mL.Combine 2.5mLof this solution with 2.5mLof Internal standard solution,dilute quantitatively with methanol to 10.0mL,and mix.

Assay preparation— Dilute an accurately measured volume of Injection quantitatively with methanol to obtain a solution containing about 0.5mg of azaperone per mL.Combine 2.5mLof this solution with 2.5mLof Internal standard solution,dilute quantitatively with methanol to 10.0mL,and mix.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with 243-nm detector and a 4.6-mm ×25-cm column that contains packing L1.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 azaperone and internal standard peaks is not less than 2.7;and the relative standard deviation for replicate injections is not more than 2.0%.

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.Calculate the quantity,in mg,of azaperone (C19H22FN3O)in each mLof the Injection taken by the formula: in which Cis the concentration,in mg per mL,of USP Azaperone RSin the Standard preparation;Lis the labeled quantity,in mg,of azaperone in each mLof the Injection;Dis the concentration,in mg per mL,of azaperone in the Assay preparation,based on the volume of Injection taken and the extent of dilution;and RUand RSare the ratios of the azaperone peak to the benzophenone peak obtained from the Assay preparationand the Standard preparation,respectively.