A: Infrared Absorption 197F.

B: Ultraviolet Absorption 197U—

Test solution— Use the Assay preparation.

Chromatographic system— Proceed as directed in the Assay. To evaluate the system suitability requirements, use the Standard preparation, as prepared in the Assay.

Procedure— Inject a volume (about 1 µL) of the Test solution into the chromatograph, record the chromatogram, and measure all of the peak responses. Calculate the percentage of each impurity in the portion of Octisalate taken by the formula: in which ri is the peak response for each impurity, and rs is the sum of the responses of all the peaks: not more than 0.5% of any individual impurity is found; and not more than 2.0% of total impurities is found.

Standard preparation— Dissolve an accurately weighed quantity of USP Octisalate RS in tert-butyl methyl ether, and dilute quantitatively, and stepwise if necessary, with tert-butyl methyl ether to obtain a solution having a known concentration of about 20.0 mg per mL.

Assay preparation— Transfer about 2 g of Octisalate, accurately weighed, to a 100-mL volumetric flask, dilute with tert-butyl methyl ether to volume, and mix.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 0.32-mm × 25-m column coated with a 0.1-µm film of phase G1. The carrier gas is helium, flowing at a rate of about 6 mL per minute. The chromatograph is programmed as follows. Initially the temperature of the column is equilibrated at 60, then the temperature is increased at a rate of 8 per minute to 240, and is maintained at 240 for 10 minutes. The injection port temperature is maintained at 240, and the detector temperature is maintained at 260. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between octisalate and any other peak 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 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 C15H22O3 in the portion of Octisalate taken by the formula: in which C is the concentration, in mg per mL, of USP Octisalate RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.