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

B: Shake a quantity of finely powdered Tablets, equivalent to about 100 mg of pyridostigmine bromide, with 20 mL of water for 5 minutes, and filter the mixture: the filtrate responds to the tests for Bromide 191.

Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 60 minutes.

Procedure— Determine the amount of C9H13BrN2O2 dissolved from UV absorbances at the wavelength of maximum absorbance at about 270 nm of filtered portions of the solution under test, suitably diluted with water, in comparison with a Standard solution having a known concentration of USP Pyridostigmine Bromide RS in the same medium.

Tolerances— Not less than 80% (Q) of the labeled amount of C9H13BrN2O2 is dissolved in 60 minutes.

Buffer solution— Mix 11.2 g of phosphoric acid with 500 mL of water, and adjust with a 50% solution of sodium hydroxide in water to a pH of 7.0. Dilute with water to 1000 mL.

Mobile phase— Dissolve 1 g of sodium 1-heptanesulfonate in 500 mL of water in a 1000-mL volumetric flask, and add 5.0 mL of triethylamine and 100 mL of acetonitrile. Dilute with water to volume, and mix. Adjust with phosphoric acid to a pH of 3.0. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Pyridostigmine Bromide RS in Buffer solution, and dilute quantitatively, and stepwise if necessary, to obtain a solution having a known concentration of 0.25 mg per mL.

Assay preparation— Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of pyridostigmine bromide, to a 200-mL volumetric flask, add 100 mL of Buffer solution, and shake for 30 minutes. Dilute with Buffer solution to volume, mix, and centrifuge. Use a portion of the supernatant as the Assay preparation.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 270-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 2 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 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 C9H13BrN2O2 in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Pyridostigmine Bromide RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.