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Standard preparation— Dissolve an accurately weighed quantity of USP Homosalate RSin chloroform,and dilute quantitatively,and stepwise if necessary,with chloroform to obtain a solution having a known concentration of about 5.0mg per mL.

Assay preparation— Dissolve about 50mg of Homosalate,accurately weighed,in 10mLof chloroform,and mix.

Chromatographic system (see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector and a 0.53-mm ×30-m column coated with a 1-µm film of G27.Hydrogen is used as the carrier gas at a flow rate of about 6mLper minute.The chromatograph is programmed as follows.Initially the temperature of the column is equilibrated at 70;upon injection the temperature is increased at a rate of 6per minute to 220,and is held at 220for 5minutes.The injection port temperature is maintained at 270,and the detector is maintained at 270.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.98for the cis-isomer and 1.0for the trans-isomer;the resolution,R,between the cis-isomer and the trans-isomer is not less than 1.0;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 chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C16H22O3in the portion of Homosalate taken by the formula: in which Cis the concentration,in mg per mL,of USP Homosalate RSin the Standard preparation;and rUand rSare the sums of the peak responses for the cis-and trans-isomers obtained from the Assay preparationand the Standard preparation,respectively.