Mobile phase— Prepare a filtered and degassed mixture of 530 mL of water and 470 mL of methanol containing about 6.35 g of dl-10-camphorsulfonic acid sodium salt and 0.8 g of ammonium nitrate. Adjust with glacial acetic acid, if necessary, to a pH of between 5.0 and 5.5. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve an accurately weighed quantity of USP Guanadrel Sulfate RS in Mobile phase to obtain a solution having a known concentration of about 10 mg per mL.

Assay preparation— Transfer about 100 mg of Guanadrel Sulfate, accurately weighed, to a container, add 10.0 mL of Mobile phase, and mix.

Resolution solution— Dissolve suitable quantities of USP Guanadrel Sulfate RS and ethylparaben in Mobile phase to obtain a solution having known concentrations of about 10 mg and 12 mg, respectively, in each mL.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a refractive index detector and a 4- to 4.6-mm × 25- to 30-cm stainless steel column containing packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the resolution, R, between guanadrel and ethylparaben is not less than 1.6, and the relative retention times are about 0.8 for guanadrel and 1.0 for ethylparaben. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 2.5%.

Procedure— Separately inject equal volumes (about 25 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 (C10H19N3O2)2·H2SO4 in the portion of Guanadrel Sulfate taken by the formula: in which C is the concentration, in mg per mL, of USP Guanadrel Sulfate RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.