Standard solution— Dissolve an accurately weighed quantity of USP Clorazepate Dipotassium RSin 0.01Msodium hydroxide,and dilute quantitatively,and stepwise if necessary,with 0.01Msodium hydroxide to obtain a solution having a known concentration of about 7.6µg per mL.

Test solution— Transfer 1Tablet to a suitable container,add 200mLof 0.01Msodium hydroxide,and homogenize for not less than 3minutes.Centrifuge a portion of this solution for 15minutes,and filter the supernatant,discarding the first 20mL.Dilute an accurately measured portion of the filtrate with 0.01Msodium hydroxide to obtain a solution having a known concentration of about 7.6µg per mL.

Procedure— Concomitantly determine the absorbances of the Standard solutionand the Test solutionin 1-cm cells at the wavelength of maximum absorbance at about 231nm,with a suitable spectrophotometer,using 0.01Msodium hydroxide as the blank.

Phosphate buffer solution— Dissolve about 13.8g of monobasic sodium phosphate in 500mLof water,adjust with 1Nsodium hydroxide to a pHof 8.0,and mix.

Mobile phase— Prepare a filtered and degassed mixture of water,acetonitrile,and Phosphate buffer solution(5:4:1).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Dissolve an accurately weighed quantity of USP7-Chloro-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one RSin acetonitrile,and dilute quantitatively,and stepwise if necessary,with acetonitrile to obtain a solution having a known concentration of about 66µg per mL.Transfer 4.0mLof this solution to a 25-mLvolumetric flask,add 5.0mLof 0.7Mpotassium carbonate and 3.0mLof acetonitrile,dilute with water to volume,mix,and filter.

Test solution— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 15mg of clorazepate dipotassium,to a suitable container.Add 5mLof acetonitrile,5mLof 0.7Mpotassium carbonate,and 15mLof water,stir for 10minutes,and filter.[NOTE—Prepare fresh before each injection,and use within 3minutes.]

Chromatographic system— The liquid chromatograph is equipped with a 232-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 1.5mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms for not less than twice the retention time of 7-chloro-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one,and measure the peak responses.Calculate the quantity,in mg,of each impurity in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP7-Chloro-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one RSin the Standard solution;riis the peak response of each impurity obtained from the Test solution;and rSis the peak response for 7-chloro-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one obtained from the Standard solution:not more than 2.0%of 7-chloro-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one is found.

Mobile phase— Prepare a filtered and degassed mixture of water,acetonitrile,and a 1Msolution of tetrabutylammonium hydroxide in methanol (110:90:1),adjust with phosphoric acid to a pHof 7.7,and mix.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Dissolve an accurately weighed quantity of USP2-Amino-5-chlorobenzophenone RSin acetonitrile,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 0.25mg per mL.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with a mixture of 0.1mMsodium hydroxide and acetonitrile (7:3)to volume,and mix.Transfer 15mLof this solution to a 50-mLvolumetric flask,dilute with a mixture of 0.1mMsodium hydroxide and acetonitrile (7:3)to volume,and mix.

Test solution— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 15mg of clorazepate dipotassium,to a suitable container,add 10mLof a mixture of 0.1mMsodium hydroxide and acetonitrile (7:3),mix,shake by mechanical means for 10minutes,and filter.

Chromatographic system— The liquid chromatograph is equipped with a 238-nm detector and a 3.9-mm ×30-cm column that contains packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard solution,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the quantity,in mg,of each impurity in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of USP2-Amino-5-chlorobenzophenone RSin the Standard solution;riis the peak response of each impurity obtained from the Test solution;and rSis the response of the 2-amino-5-chlorobenzophenone peak obtained from the Standard solution:the sum of all impurities,other than 7-chloro-1,3-dihydro-5-phenyl-2H-1,4-benzodiazepin-2-one,found in Method Iand Method IIis not more than 0.5%.

1333C(rU/rS),