Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 30minutes.

Procedure— Determine the amount of C22H31NO3·HCl dissolved using the method set forth in the Assay,making any necessary modifications to the concentration of the Standard preparationto correspond to that of the solution under test.

Tolerances— Not less than 80%(Q)of the labeled amount of C22H31NO3·HCl is dissolved in 30minutes.

Solvent A— Add about 0.9mLof triethylamine to a filtered and deaerated mixture of water and methanol (3200:800).Adjust with phosphoric acid to a pHof 3.5±0.05.

Mobile phase— Prepare a degassed and filtered mixture of Solvent Aand acetonitrile (80:20).

Standard preparation— Prepare a solution of USP Oxybutynin Chloride RSin Mobile phasehaving an accurately known concentration of about 0.05mg per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 50mg of oxybutynin chloride,to a 1000-mLvolumetric flask,add about 400mLof Mobile phase,sonicate for about 10minutes,shake by mechanical means for about 45minutes,dilute with Mobile phaseto volume,and mix.

Chromatographic system— The liquid chromatograph is equipped with a 203-nm detector,and a 4-mm ×30-cm column that contains packing L10.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the chromatogram as directed for Procedure:the tailing factor is not more than 2.0,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 C22H31NO3·HCl in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP Oxybutynin Chloride RSin the Standard preparation,and rUand rSare the oxybutynin peak responses obtained from the Assay preparationand the Standard preparation,respectively.