A: It responds to the Identification test under Physostigmine.

B: It responds to the tests for Salicylate 191.

0.05 M Ammonium acetate— Dissolve 3.85 g of ammonium acetate in 1 L of water, and adjust, if necessary, with glacial acetic acid or ammonium hydroxide to a pH of 6 ± 0.1.

Mobile phase— Prepare a filtered and degassed mixture of equal volumes of acetonitrile and 0.05 M Ammonium acetate. Make adjustments if necessary (see System Suitability under Chromatography 621).

Benzyl alcohol–benzaldehyde solution— Prepare a mixture of 100 µL of USP Benzyl Alcohol RS and 1 µL of benzaldehyde in 400 mL of acetonitrile.

Standard preparation— Dissolve an accurately weighed quantity of USP Physostigmine Salicylate RS in Benzyl alcohol–benzaldehyde solution, and dilute quantitatively, and stepwise if necessary, with Benzyl alcohol–benzaldehyde solution to obtain a solution having a known concentration of about 30 µg per mL.

Assay preparation— Transfer an accurately measured volume of Injection, equivalent to about 3 mg of physostigmine salicylate, to a 100-mL volumetric flask, dilute with acetonitrile to volume, and mix.

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. Separately chromatograph 10-µL portions of the Benzyl alcohol–benzaldehyde solution and the Standard preparation, and record the peak responses as directed for Procedure [note—If the components of the Benzyl alcohol–benzaldehyde solution co-elute, the Standard preparation will exhibit only two peaks instead of three]: in a suitable system, benzyl alcohol and benzaldehyde elute before physostigmine; the resolution, R, between the physostigmine peak and the adjacent peak (benzyl alcohol or benzaldehyde or the combination of these) is not less than 2.0; the column efficiency determined from the analyte peak is not less than 1200 theoretical plates; and the relative standard deviation for replicate injections is not more than 2.0%.

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 physostigmine salicylate (C15H21N3O2·C7H6O3) in each mL of the Injection taken by the formula: in which C is the concentration, in µg per mL, of USP Physostigmine Salicylate RS in the Standard preparation; V is the volume, in mL, of Injection taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.