A: Infrared Absorption 197K.

B: The residue obtained by ignition meets the requirements of the test for pyrophosphate as described under Phosphate 191.

C: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

1-Pentanesulfonate sodium solution— Add about 960 mg of sodium 1-pentanesulfonate and 1 mL of glacial acetic acid to 400 mL of water, and mix.

Mobile phase— Prepare a filtered and degassed mixture of methanol and 1-Pentanesulfonate sodium solution (60:40). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer an accurately weighed quantity of USP Primaquine Phosphate RS to a suitable volumetric flask, and dilute with Mobile phase to volume to obtain a solution having a known concentration of about 0.2 mg per mL.

System suitability solution— Dissolve suitable quantities of 8-amino-6-methoxyquinoline in the Standard preparation to obtain a solution containing about 0.002 mg per mL.

Assay preparation— Transfer an accurately weighed quantity of Primaquine Phosphate to a suitable volumetric flask, and dilute with Mobile phase to volume to obtain a solution having a known concentration of about 0.2 mg per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 264-nm detector and a 3.0-mm × 15-cm column that contains 3-µm packing L1. The column is maintained at 30. The flow rate is about 0.6 mL per minute. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between the primaquine and 8-amino-6-methoxyquinoline peaks is not less than 5.0; the resolution R, between primaquine and any adjacent peak is not less than 2.0; and the tailing factor for the primaquine peak is not more than 1.8. Chromatograph replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation is not more than 1.0%.

Procedure— Separately inject equal volumes (about 5 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 percentage, of C15H21N3O·2H3PO4 in the portion of Primaquine Phosphate taken by the formula: in which CS is the concentration, in mg per mL, of USP Primaquine Phosphate RS in the Standard preparation; CU is the concentration, in mg per mL, of Primaquine Phosphate in the Assay preparation, based on the weighed amount; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.