Mobile phase— Dissolve 3.4g of monobasic potassium phosphate in about 850mLof water,adjust with phosphoric acid to a pHof 3.0±0.05,dilute with water to 1000mL,mix,and pass through a suitable filter having a 0.5-µm or finer porosity.Prepare a mixture of methanol and this solution (650:350),and degas.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Internal standard solution— Prepare a solution in Mobile phasecontaining about 0.25mg of hexanophenone per mL.

Standard preparation— Transfer about 40mg of USP Hexylresorcinol RS,accurately weighed,to a 100-mLvolumetric flask,dissolve in Mobile phase,dilute with Mobile phaseto volume,and mix.Transfer 10.0mLof this solution and 10.0mLof Internal standard solutionto a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.This solution contains about 0.08mg of USP Hexylresorcinol RSper mL.

Assay preparation— Weigh and pulverize not fewer than 20Lozenges.Transfer an accurately weighed portion of the powder,equivalent to about 4mg of hexylresorcinol,to a 50-mLvolumetric flask,add 10.0mLof Internal standard solutionand 20mLof Mobile phase,and shake until dissolved.Dilute with Mobile phaseto volume,and mix.Filter a portion of this solution through a suitable filter of 0.5µm or finer porosity,and use the filtrate as the Assay preparation.

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with a 280-nm detector and a 4.6-mm ×15-cm column that contains packing L7and is maintained at 37±2.The flow rate is about 1.5mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed under Procedure:the relative retention times are about 0.6for hexylresorcinol and 1.0for hexanophenone,the tailing factor is not less than 0.9and not more than 1.4,the column efficiency is not less than 1500theoretical plates,and the relative standard deviation for replicate injections is not more than 2.0%.Inject the Assay preparation,and record the peak responses as directed under Procedure:the resolution,R,between the hexylresorcinol peak and the nearest adjacent peak is not less than 1.2.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C12H18O2in the portion of Lozenges taken by the formula: in which Cis the concentration,in mg per mL,of USP Hexylresorcinol RSin the Standard preparation,and RUand RSare the ratios of the responses of the hexylresorcinol peak and the hexanophenone peak obtained from the Assay preparationand the Standard preparation,respectively.