A: Infrared Absorption 197K.

B: Standard solution—Use the Standard solution containing 0.2 mg of USP Procainamide Hydrochloride RS per mL, prepared as directed under Ordinary impurities.

Test solution— Dilute the Test solution, prepared as directed under Ordinary impurities, with methanol to obtain a solution containing about 0.2 mg of procainamide hydrochloride per mL.

Adsorbent, Eluant, and Visualization— Prepare as directed in Ordinary impurities.

Procedure— Proceed as directed for Procedure under Ordinary impurities 466: the RF value of the principal spot obtained from the Test solution corresponds to that obtained from the Standard solution.

Test solution: methanol.

Standard solution: methanol.

Adsorbent: chromatographic silica gel.

Eluant: a mixture of chloroform, methanol, and ammonium hydroxide (70:30:0.7).

Visualization: 1, followed by spraying with a 1 in 2000 solution of fluorescamine in acetone and viewing with UV light at 366 nm.

Mobile phase and Resolution solution— Proceed as directed in the Assay.

Standard solution— Quantitatively dissolve an accurately weighed quantity of USP Aminobenzoic Acid RS in Mobile phase to obtain a solution having a known concentration of about 0.25 µg per mL.

Test solution— Transfer 25.0 mL of the stock solution used to prepare the Assay preparation to a 50-mL volumetric flask, dilute with Mobile phase to volume, and mix. This solution contains about 0.25 mg of procainamide hydrochloride per mL.

Chromatographic system— Proceed as directed for Chromatographic system in the Assay. In addition, the tailing factor for the p-aminobenzoic acid peak in the chromatogram obtained from the Resolution solution is not more than 2.0; and the relative standard deviation for replicate injections of the Standard solution is not more than 3.0%.

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 the p-aminobenzoic acid peaks. Calculate the percentage of p-aminobenzoic acid in the portion of Procainamide Hydrochloride taken by the formula: in which C is the concentration, in µg per mL, of USP Aminobenzoic Acid RS in the Standard solution; W is the weight, in mg, of Procainamide Hydrochloride taken to prepare the stock solution for the Assay preparation; and rU and rS are the p-aminobenzoic acid peak responses obtained from the Test solution and the Standard solution, respectively. The limit is 0.1%.

Mobile phase— Prepare a suitable mixture of water, methanol, and triethylamine (140:60:1); adjust with phosphoric acid to a pH of 7.5 ± 0.1; filter; and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Quantitatively dissolve an accurately weighed quantity of USP Procainamide Hydrochloride RS in Mobile phase to obtain a solution having a known concentration of about 0.5 mg per mL. Quantitatively dilute an accurately measured volume of this stock solution with Mobile phase to obtain a Standard preparation having a known concentration of about 0.05 mg per mL.

Resolution solution— Dissolve a quantity of p-aminobenzoic acid in Mobile phase to obtain a solution containing about 0.1 mg per mL. Pipet 10 mL of this solution and 10 mL of the stock solution used to prepare the Standard preparation to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Assay preparation— Transfer about 50 mg of Procainamide Hydrochloride, accurately weighed, to a 100-mL volumetric flask; dissolve in and dilute with Mobile phase to volume and mix. Transfer 10.0 mL of this stock solution to a second 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 280-nm detector and a 3.9-mm × 30-cm column that contains 10-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between the p-aminobenzoic acid and procainamide peaks is not less than 5.0. The relative retention times are about 0.5 for p-aminobenzoic acid and 1.0 for procainamide hydrochloride. 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 C13H21N3O·HCl in the portion of Procainamide Hydrochloride taken by the formula: in which C is the concentration, in mg per mL, of USP Procainamide Hydrochloride RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.