Cupric sulfate solution— Dissolve 250 mg of cupric sulfate and 4.5 g of ammonium acetate in sufficient 2 N acetic acid to obtain 100 mL of solution.

4-Amino-3-hydroxy-1-naphthalenesulfonic acid solution— Grind in a mortar 5 g of sodium sulfite, 94.3 g of sodium metabisulfite, and 700 mg of 4-amino-3-hydroxy-1-naphthalenesulfonic acid. Dissolve 1.5 g of this mixture in 10 mL of water, heating gently if necessary. Use this solution only when freshly prepared.

Standard solution— Dissolve 143.3 mg of dried monobasic potassium phosphate in water to make 1000 mL of solution. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, dilute with water to volume, and mix. This solution contains the equivalent of 5 µg of phosphate (PO4) in each mL.

Test solution— Add 30 mL of water to 500 mg of specimen, and heat to boiling. Allow to cool, and filter, collecting the filtrate in a 50-mL volumetric flask. Wash the filter with water, collecting the washings in the volumetric flask, dilute with water to volume, and mix.

Procedure— Treat 10 mL of Test solution and 10 mL of Standard solution as follows. To each add 5 mL of Cupric sulfate solution, 2 mL of ammonium molybdate solution (3 in 100), 1 mL of 4-Amino-3-hydroxy-1-naphthalenesulfonic acid solution, and 1 mL of perchloric acid solution (3 in 100), mix, and allow to stand for 15 minutes: the Test solution does not have a blue color that is darker than that of the Standard solution (0.05%).

Mobile phase and Chromatographic system— Prepare as directed in the Assay.

Standard preparation— Dissolve accurately weighed quantities of USP Praziquantel Related Compound A RS, USP Praziquantel Related Compound B RS, and USP Praziquantel Related Compound C RS in Mobile phase to obtain a single solution having known concentrations of about 0.04 mg of each per mL.

Test preparation— Transfer about 200 mg of Praziquantel, accurately weighed, to a 10-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Test preparation into the chromatograph, record the chromatograms, and measure the responses for the peaks. The relative retention times are about 0.8 for praziquantel related compound A, 1.0 for praziquantel, 1.8 for praziquantel related compound B, and 2.1 for praziquantel related compound C. Calculate, in turn, the percentages of 2-benzoyl-1,2,3,6,7,11b-hexahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (praziquantel related compound A), 2-(cyclohexylcarbonyl)-2,3,6,7-tetrahydro-4H-pyrazino[2,1-a]isoquinolin-4-one (praziquantel related compound B), and 2-(N-formylhexahydrohippuroyl)-1,2,3,4-tetrahydroisoquinolin-1-one (praziquantel related compound C) in the portion of Praziquantel taken by the formula: in which C is the concentration, in mg per mL, of the respective USP Reference Standard taken to prepare the Standard preparation; W is the weight, in mg, of Praziquantel taken to prepare the Test preparation; and rU and rS are the peak responses at corresponding retention times, obtained from the Test preparation and the Standard preparation, respectively. Not more than 0.2% of each is found.

(Official January 1, 2007)

Mobile phase— Prepare a suitable degassed mixture of acetonitrile and water (60:40). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Praziquantel RS in Mobile phase, and dilute quantitatively, and stepwise if necessary, with Mobile phase to obtain a solution having a known concentration of about 0.18 mg per mL.

Assay preparation— Transfer about 36 mg of Praziquantel, accurately weighed, to a 20-mL volumetric flask, dissolve in and dilute with Mobile phase to volume, and mix. Transfer 5.0 mL of the solution so obtained 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 210-nm detector and a 4-mm × 25-cm column that contains 10-µm packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10 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 C19H24N2O2 in the portion of Praziquantel taken by the formula: in which C is the concentration, in mg per mL, ofUSP Praziquantel RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.