A: Infrared Absorption á197Kñ.

B: Ultraviolet Absorption á197Uñ—

Standard solution— Use the Standard preparationprepared as directed in the Assay.

Test solution— Use the Assay preparation.

Chromatographic system— Proceed as directed in the Assay.

Procedure— Separately inject equal volumes (about 1µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the percentage of each impurity in the portion of Methyl Benzylidene Camphor taken by the formula: in which riis the peak response for each impurity obtained from the Test solution;and rSis the peak response for methyl benzylidene camphor obtained from the Standard solution:not more than 0.02%of camphor is found;not more than 0.1%of any other individual impurity is found;and not more than 0.5%of total impurities is found.

Standard preparation— Dissolve accurately weighed quantities of camphor and USP Methyl Benzylidene Camphor RSin dichloromethane,and dilute quantitatively,and stepwise if necessary,with dichloromethane to obtain a solution having a known concentration of about 250µg per mLfor each compound.

Assay preparation— Transfer about 25mg of Methyl Benzylidene Camphor,accurately weighed,to a 100-mLvolumetric flask,and dissolve in and dilute with dichloromethane to volume.

Chromatographic system (see Chromatography á621ñ)— The gas chromatograph is equipped with a flame-ionization detector and a 0.32-mm ×30-m fused-silica capillary column coated with a 0.25-µm layer of phase G1.The carrier gas is helium,flowing at a rate of about 1.2mLper minute.The chromatograph is programmed as follows.Initially the temperature of the column is equilibrated at 100,then 5minutes after injection the temperature is increased at a rate of 10per minute to 230,and maintained at 230for 10minutes.The temperature is then increased at a rate of 10per minute to 300,and maintained at 300until the end of the procedure.The injection port temperature is maintained at 295and the detector temperature is maintained at 305.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.2for camphor and 1.0for methyl benzylidene camphor;the tailing factor is not more 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 C18H22Oin the portion of Methyl Benzylidene Camphor taken by the formula: in which Cis the concentration,in mg per mL,of USP Methyl Benzylidene Camphor RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.