Sodium chloride solution— Dissolve 250g of sodium chloride in water to make 1000mL.

Internal standard solution— Dissolve suitable quantities of anethole in hexanes to obtain a solution having a concentration of about 2mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Menthol RSin Internal standard solutionto obtain a solution having a known concentration of about 0.20Lmg per mL,Lbeing the labeled quantity,in mg,of menthol in each Lozenge.

Assay preparation— Transfer 20Lozenges to a 1-liter screw-capped conical flask.[NOTE—Use caps with inert white rubber liners.]Add 200mLof water,260mLof Sodium chloride solution,and 100.0mLof Internal standard solution,and shake by mechanical means for 30minutes.Allow the phases to separate,and transfer a portion of the hexanes phase to a suitable container.

Chromatographic system (see Chromatography á621ñ)—The gas chromatograph is equipped with a flame-ionization detector,a split injection system with a split ratio of about 10:1,and a 0.53-mm ×30-m fused silica column coated with a 1-µm layer of Gl6stationary phase.The column is maintained isothermally at about 125,and the injection port and the detector block are maintained at about 250.The carrier gas is helium at a flow rate of about 10mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.5for menthol and 1.0for anethole,the resolution,R,between the menthol and the anethole peaks is not less than 15,the tailing factor for the menthol and anethole peaks is not more than 2.0,and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 1µL)of the Standard preparationand the Assay preparationinto the gas chromatograph,and measure the responses for the menthol and anethole peaks.Calculate the quantity,in mg,of C10H20Oin each Lozenge taken by the formula: in which Cis the concentration,in mg per mL,of USP Menthol RSin the Standard preparation,and RUand RSare the ratios of the menthol peak to the anethole peak obtained from the Assay preparationand the Standard preparation,respectively.