Assay—
Dilute phosphoric acid solution—
Transfer 10 mL of phosphoric acid to a 100-mL volumetric flask containing 50 mL of water, and mix. Dilute with water to volume, and mix.
Tetraethylammonium chloride solution—
Transfer about 170 mg of tetraethylammonium chloride to a 1-liter volumetric flask, add 3.4 mL of Dilute phosphoric acid solution, and add water to dissolve the mixture. Dilute with water to volume, and mix.
Mobile phase—
Prepare a filtered and degassed mixture of acetonitrile and
Tetraethylammonium chloride solution (52:48). Make adjustments if necessary (see
System Suitability under
Chromatography 
621
).
Standard preparation—
Dissolve a suitable quantity of
USP Pralidoxime Chloride RS, accurately weighed, in water to obtain a
Standard solution having a known concentration of about 1.25 mg per mL. (Reserve a portion of the
Standard solution for the
System suitability preparation.) Pipet 2.0 mL of this solution into a 100-mL volumetric flask, dilute with
Mobile phase to volume, and mix.
Assay preparation—
Transfer about 62.5 mg of Pralidoxime Chloride, accurately weighed, to a 50-mL volumetric flask, dissolve in water, dilute with water to volume, mix, and filter. Pipet 2.0 mL of this solution into a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.
System suitability preparation—
Prepare a solution of pyridine-2-aldoxime in water having a concentration of 0.65 mg per mL. Transfer 2.0 mL of this solution to a 100-mL volumetric flask, add 2.0 mL of the Standard solution, dilute with Mobile phase to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 270-nm detector and a 3- to 5-mm × 25-cm column containing 5-µm packing L1. The flow rate is about 1.2 mL per minute. Chromatograph the
Standard preparation and the
System suitability preparation by injecting about 15 µL of these preparations, and record the peak responses as directed for
Procedure: the resolution,
R, between the pyridine-2-aldoxime and pralidoxime chloride peaks is not less than 4.0; the column efficiency determined from the analyte peak is not less than 4000 theoretical plates; the tailing factor for the analyte peak is not more than 2.5; and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 15 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.6 for pyridine-2-aldoxime and 1.0 for pralidoxime chloride. Calculate the quantity, in mg, of C
7H
9ClN
2O in the portion of Pralidoxime Chloride taken by the formula:
2.5C(rU / rS),
in which
C is the concentration, in µg per mL, of
USP Pralidoxime Chloride RS in the
Standard preparation; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
;)
for 3 hours: it loses not more than 2.0% of its weight.