Medium: water;900mL.

Apparatus 1: 100rpm.

Time: 45minutes.

Procedure— Determine the amount of C18H18ClN3Odissolved from UVabsorbances at 254nm using filtered portions of the solution under test,diluted with water,if necessary,in comparison with a Standard solution having a known concentration of USP Loxapine Succinate RSin the same medium.

Tolerances— Not less than 75%(Q)of the labeled amount of C18H18ClN3Ois dissolved in 45minutes.

Mobile phase— Dissolve 4g of tetramethylammonium chloride in 800mLof water,add 200mLof acetonitrile and 1mLof phosphoric acid,mix,filter,and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Loxapine Succinate RSin 0.01Nhydrochloric acid,and dilute quantitatively with Mobile phaseto obtain a solution having a known concentration of about 0.136mg (equivalent to 0.1mg of loxapine base)per mL.

Assay preparation— Weigh and mix the contents of not less than 20Capsules.Transfer an accurately weighed portion of the Capsules'contents,equivalent to 50mg of loxapine,to a 500-mLvolumetric flask,add 50mLof 0.1Nhydrochloric acid,shake,and sonicate for 5minutes.Dilute with Mobile phaseto volume,and filter,discarding the first 8mLof the filtrate.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×15-cm column that contains 5-µm packing L10.The flow rate is about 1.6mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the tailing factor for the analyte peak is not more than 2.0,the column efficiency determined from the analyte peak is not less than 1500theoretical plates,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)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 C18H18ClN3Oin the portion of Capsules taken by the formula: in which 327.82and 445.91are the molecular weights of loxapine base and loxapine succinate,respectively,Cis the concentration,in mg per mL,of USP Loxapine Succinate RSin the Standard preparation,and rUand rSare the peak areas of the analyte obtained from the Assay preparationand the Standard preparation,respectively.