A: It meets the requirements under Identification—Organic Nitrogenous Bases 181.

B: It meets the requirements of the test for Citrate 191.

Test solution: methanol.

Standard solution: methanol.

Eluant: a mixture of methanol and ammonium hydroxide (100:1.5).

Visualization: 16.

Phosphate buffer, Mobile phase, and Chromatographic system— Proceed as directed in the Assay.

Standard solution— Prepare a solution of USP Diethylcarbamazine Citrate RS in Phosphate buffer having a known concentration of about 0.003 mg per mL.

Test solution— Transfer about 300 mg of Diethylcarbamazine Citrate, accurately weighed, to a 100-mL volumetric flask, add 100 mL of Phosphate buffer, and mix. Filter or centrifuge, and use the clear filtrate or supernatant.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for all the peaks. Calculate the percentage of each impurity in the portion of Diethylcarbamazine Citrate taken by the formula: in which C is the concentration, in mg per mL, of USP Diethylcarbamazine Citrate RS in the Standard solution; W is the weight, in mg, of Diethylcarbamazine Citrate taken to prepare the Test solution; ri is the peak response for each impurity obtained from the Test solution; and rS is the peak response for diethylcarbamazine citrate obtained from the Standard solution. Not more than 0.1% of any individual impurity is found.

Phosphate buffer— Dissolve 31.24 g of monobasic potassium phosphate in 1000 mL of water.

Mobile phase— Dissolve 10 g of monobasic potassium phosphate in 1000 mL of water. Prepare a filtered and degassed mixture of 900 mL of this solution and 100 mL of methanol.

Standard preparation— Transfer about 5 mg of USP Diethylcarbamazine Citrate RS, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Phosphate buffer to volume, and mix.

Assay preparation— Transfer about 5 mg of Diethylcarbamazine Citrate, accurately weighed, to a 50-mL volumetric flask, dissolve in and dilute with Phosphate buffer to volume, and mix.

Chromatographic system— The liquid chromatograph is equipped with a 220-nm detector and a 3.9-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 0.8 mL per minute. Chromatograph the Standard preparation, 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 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C10H21N3O·C6H8O7 in the portion of Diethylcarbamazine Citrate taken by the formula: in which C is the concentration, in mg per mL, of USP Diethylcarbamazine Citrate RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.