Solution: 10µg per mL,filtered.

Medium: 0.1Nhydrochloric acid.

Mobile phase— To 4.5g of sodium 1-hexanesulfonate add 1500mLof water,400mLof methanol,and 100mLof acetonitrile,mix,and allow to cool to room temperature.Adjust with phosphoric acid to a pHof 5.1,and pass through a filter having a 0.5-µm or finer porosity.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Quantitatively dissolve an accurately weighed quantity of USP Amprolium RSin water to obtain a solution having a known concentration of about 0.5mg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 960mg of amprolium,to a 100-mLvolumetric flask,dilute with water to volume,and mix.Transfer 5.0mLof this stock solution to a second 100-mLvolumetric flask,dilute with water to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 268-nm detector and a 3.9-mm ×30-cm column that contains packing L11.The column is maintained at a constant temperature of about 45.The flow rate is about 1mLper 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 2.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak areas for amprolium.Calculate the quantity,in mg,of amprolium (C14H19ClN4·HCl)in each mLof the Oral Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Amprolium RSin the Standard preparation;Vis the volume,in mL,of Oral Solution taken to prepare the Assay preparation;and rUand rSare the amprolium peak areas obtained from the Assay preparationand the Standard preparation,respectively.