A: Dilute 0.1 mL of the filtrate with 1 mL of water, and add 1 drop of gold chloride TS: a violet-blue color is produced at once.

B: To the remainder of the filtrate add 5 mL of trinitrophenol TS: a yellow precipitate is formed. Wash the precipitate with cold water, and dry at 105 for 2 hours: the picrate melts between 208 and 215. [Caution—Picrates may explode.]

Medium: 0.01 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 60 minutes.

1-Pentanesulfonate sodium solution— Add about 961 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).

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph replicate injections of the Standard solution and record the peak responses as directed for Procedure: the relative standard deviation is not more than 3.0%.

Procedure— Separately inject into the chromatograph equal volumes (about 20 µL) of the solution under test and a Standard solution having a known concentration of USP Primaquine Phosphate RS in the same Medium, and record the chromatograms. Measure the responses for the major peaks, and calculate the amount of C15H21N3O·2H3PO4 dissolved.

Tolerances— Not less than 80% (Q) of the labeled amount of C15H21N3O·2H3PO4 is dissolved in 60 minutes.

Procedure for content uniformity— Transfer 1 Tablet, previously crushed or finely powdered, to a 100-mL volumetric flask, add about 60 mL of Mobile phase, mix, and sonicate for about 3 minutes. Allow to cool, dilute with Mobile phase to volume, and mix. Pipet 8.0 mL of this solution into a 10-mL volumetric flask, dilute with Mobile phase to volume, and mix. Pass a portion of the solution through a 0.2-µm polyvinylidene fluoride (PVDF) membrane filter, discard the first 5 mL, and use the filtrate.

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 a suitable quantity of 8-amino-6-methoxyquinoline in the Standard preparation to obtain a solution containing about 0.002 mg per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 10 mg of primaquine phosphate, to a 50-mL volumetric flask, add about 30 mL of Mobile phase, mix, and sonicate for about 3 minutes. Allow to cool, dilute with Mobile phase to volume, and mix. Pass a portion of the solution through a 0.2-µm PVDF filter, discard the first 5.0 mL, and use the filtrate.

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 other 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 percentage of the labeled amount of primaquine phosphate (C15H21N3O·2H3PO4) in the portion of Tablets 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 labeled claim per Tablet; rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively; and 100 is the percentage factor.