A: Infrared Absorption 197K.

B: Ultraviolet Absorption 197U—

Standard solution— Use the Standard preparation prepared 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 1 µL) of the Standard solution and the Test solution into 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 ri is the peak response for each impurity obtained from the Test solution; and rS is 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.

(Official January 1, 2007)

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

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

Chromatographic system (see Chromatography 621)— 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 1.2 mL per minute. The chromatograph is programmed as follows. Initially the temperature of the column is equilibrated at 100, then 5 minutes after injection the temperature is increased at a rate of 10 per minute to 230, and maintained at 230 for 10 minutes. The temperature is then increased at a rate of 10 per minute to 300, and maintained at 300 until the end of the procedure. The injection port temperature is maintained at 295 and 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 0.2 for camphor and 1.0 for 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 1 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C18H22O in the portion of Methyl Benzylidene Camphor taken by the formula: in which C is the concentration, in mg per mL, of USP Methyl Benzylidene Camphor RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.