A: Infrared Absorption 197K.

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

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

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

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

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

Mobile phase— Use variable mixtures of Solution A and Solution B as directed for Chromatographic system. Make adjustments if necessary (see System Suitability under Chromatography 621).

Resolution solution— Prepare a solution of indole and USP Dolasetron Mesylate RS in Diluent having known concentrations of about 0.004 mg per mL and 0.03 mg per mL, respectively.

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

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

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

Chromatographic system (see Chromatography 621)— 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 1.5 mL per 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 105 for about 16 hours. Retest the column.] Chromatograph Standard solution 1, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 5.0%.

Procedure— Separately inject equal volumes (about 100 µL) of Standard solution 1, Standard solution 2, and the Test solution into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the percentage of dolasetron mesylate related compound A in the portion of Dolasetron Mesylate taken by the formula: in which 181.2 and 217.8 are the molecular weights of dolasetron mesylate related compound A base and dolasetron mesylate related compound A hydrochloride, respectively; CRC is the concentration, in mg per mL, of USP Dolasetron Mesylate Related Compound A RS in Standard solution 2; W is the weight, in mg, of Dolasetron Mesylate taken to prepare the Test solution; and rU and rS are the peak areas for dolasetron mesylate related compound A obtained from the Test solution and Standard solution 2, respectively: not more than 0.1% of dolasetron mesylate related compound A is 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 C is the concentration, in mg per mL, of USP Dolasetron Mesylate RS in Standard solution 1; W is as defined above; ri is the peak area for each impurity obtained from the Test solution; and rS is 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 1 M ammonium formate (450:440:110), adding 0.19 mL of triethylamine to the acetonitrile portion. Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Chromatographic system (see Chromatography 621)— 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 1 mL per 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 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantity, in mg, of C19H20N2O3·CH4O3S·H2O in the portion of Dolasetron Mesylate taken by the formula: in which C is the concentration, in mg per mL, of USP Dolasetron Mesylate RS in the Standard preparation; and rU and rS are the peak areas obtained from the Assay preparation and the Standard preparation, respectively.