A:Infrared Absorption á197Kñ.

B: Transfer about 5to 10mg of 5,5¢-methylenedisalicylic acid to a clean crucible,and heat in an oven at 150for 5minutes.Remove from the oven,and add about 10drops of solution prepared by dissolving 0.1g of Dolasetron Mesylate in 100mL.Return to the oven,and evaporate to dryness:a red or pink color (presence of methanesulfonic acid)develops in the white residue.

0.01M Dibasic ammonium phosphate solution— Dissolve 132.1g of dibasic ammonium phosphate in 1000mLof water.Dilute 10.0mLof this solution with about 990mLof water,adjust with 2.0Mphosphoric acid to a pHof 7.0,and mix.

Diluent— Prepare a mixture of water and acetonitrile (4:1).

Solution A— Prepare a filtered and degassed mixture of 0.01M Dibasic ammonium phosphate solutionand acetonitrile (1000:53).

Solution B— Prepare a filtered and degassed mixture of acetronitrile and 0.01M Dibasic ammonium phosphate solution(795:295).

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Resolution solution— Prepare a solution of indole and USP Dolasetron Mesylate RSin Diluenthaving known concentrations of about 0.004mg per mLand 0.03mg per mL,respectively.

Standard solution 1— Dissolve an accurately weighed quantity of USP Dolasetron Mesylate RSin Diluent,and dilute quantitatively,and stepwise if necessary,with Diluentto obtain a solution having a known concentration of about 0.03mg per mL.

Standard solution 2— Dissolve accurately weighed quantities of USP Dolasetron Mesylate RSand USP Dolasetron Mesylate Related Compound A RSin Diluent,and dilute quantitatively,and stepwise if necessary,with Diluentto obtain a solution having known concentrations of about 6mg per mLand 0.0072mg per mL,respectively.

Test solution— Transfer about 150mg of Dolasetron Mesylate,accurately weighed,to a 25-mLvolumetric flask,dissolve in and dilute with Diluentto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm ×25-cm column that contains packing L7.The flow rate is about 1.5mLper minute.The chromatograph is programmed as follows. Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the resolution,R,between the first eluting peak,indole,and the second eluting peak,dolasetron mesylate,is not less than 1.5.[NOTE—If the dolasetron mesylate peak is found to elute before the indole peak,condition the column as follows.Fill up the column with Solution A,plug the column,and place the column in a convection oven at 105for about 16hours.Retest the column.]Chromatograph Standard solution 1,and record the peak responses as directed forProcedure:the relative standard deviation for replicate injections is not more than 5.0%.

Procedure— Separately inject equal volumes (about 100µL)of Standard solution 1,Standard solution 2,and the Test solutioninto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the percentage of dolasetron mesylate related compound Ain the portion of Dolasetron Mesylate taken by the formula: in which 181.2and 217.8are the molecular weights of dolasetron mesylate related compound Abase and dolasetron mesylate related compound Ahydrochloride,respectively;CRCis the concentration,in mg per mL,of USP Dolasetron Mesylate Related Compound A RSin Standard solution 2;Wis the weight,in mg,of Dolasetron Mesylate taken to prepare the Test solution;and rUand rSare the peak areas for dolasetron mesylate related compound Aobtained from the Test solutionand Standard solution 2,respectively:not more than 0.1%of dolasetron mesylate related compound Ais found.Calculate the percentage of each impurity (other than dolasetron mesylate related compound A)in the portion of Dolasetron Mesylate taken by the formula: in which Cis the concentration,in mg per mL,of USP Dolasetron Mesylate RSin Standard solution 1;Wis as defined above;riis the peak area for each impurity obtained from the Test solution;and rSis the peak area for dolasetron mesylate obtained from Standard solution 1:not more than 0.1%of any individual impurity is found;and not more than 0.3%of total impurities is found.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,water,and 1Mammonium formate (450:440:110),adding 0.19mLof triethylamine to the acetonitrile portion.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve accurately weighed quantities of USP Dolasetron Mesylate RSand indole-3-carboxylic acid,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having known concentrations of about 0.04mg per mLand 0.004mg per mL,respectively.

Assay preparation— Transfer about 20mg of Dolasetron Mesylate,accurately weighed,to a 50-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.Transfer 5mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 285-nm detector and a 4.6-mm ×15-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the resolution,R,between indole-3-carboxylic acid and dolasetron mesylate is not less than 4;the tailing factor is not more than 1.8;and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the areas for the major peaks.Calculate the quantity,in mg,of C19H20N2O3·CH4O3S·H2Oin the portion of Dolasetron Mesylate taken by the formula: in which Cis the concentration,in mg per mL,of USP Dolasetron Mesylate RSin the Standard preparation;and rUand rSare the peak areas obtained from the Assay preparationand the Standard preparation,respectively.