Standard solution— Quantitatively dissolve accurately weighed quantities of 3,5-dimethylphenol and USP Chloroxylenol Related Compound A RS in chloroform to obtain a solution containing about 0.08 mg of each per mL.

Test solution— Quantitatively dissolve an accurately weighed quantity of Chloroxylenol in chloroform to obtain a solution containing about 40.0 mg per mL.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 4-mm × 1.8-m column packed with 3% phase G16 on support S1A. The carrier gas is dry nitrogen, flowing at a rate of about 30 mL per minute. The column temperature is maintained at 180, and the injection port and detector block temperatures are maintained at 200. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the resolution, R, between 3,5-dimethylphenol and chloroxylenol related compound A is not less than 4.5; and the relative standard deviation for replicate injections is not more than 10%.

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 areas for all the peaks. Calculate the percentages of 3,5-dimethylphenol (C8H10O) and chloroxylenol related compound A (C8H9ClO) in the portion of Chloroxylenol taken by the formula: in which rU and rS are the peak areas of the appropriate analyte obtained from the Test solution and the Standard solution, respectively: not more than 0.2% of 3,5-dimethylphenol or chloroxylenol related compound A is found. Calculate the percentage of each impurity in the portion of Chloroxylenol taken by the formula: in which ri is the area of each peak obtained from the Test solution, excluding that of the main chloroxylenol peak, the 3,5-dimethylphenol peak, and the chloroxylenol related compound A peak; and rs is the sum of the areas of all the peaks: not more than 0.5% of any individual impurity is found. Calculate the percentage of total impurities in the portion of Chloroxylenol taken by the formula: in which rT is the sum of the areas of all the peaks obtained from the Test solution, excluding that of the main chloroxylenol peak; and rs is the sum of the areas of all the peaks obtained from the Test solution: not more than 1.5% of total impurities is found.

(Official January 1, 2007)

Internal standard solution— Prepare a solution of p-chlorophenol in chloroform containing about 0.8 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Chloroxylenol RS in Internal standard solution to obtain a solution having a known concentration of about 1 mg per mL.

Assay preparation— Transfer about 100 mg of Chloroxylenol, accurately weighed, to a 100-mL volumetric flask, dissolve in Internal standard solution, dilute with Internal standard solution to volume, and mix.

Chromatographic system (see Chromatography 621)— The gas chromatograph is equipped with a flame-ionization detector and a 4-mm × 1.8-m column packed with 3% phase G16 on support S1A. The injection port, column, and detector block are maintained at 210. Dry nitrogen, flowing at a rate of about 30 mL per minute, is used as the carrier gas. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between the p-chlorophenol peak and the chloroxylenol peak is not less the 2.0; the tailing factor for the chloroxylenol peak is not more than 1.5; and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— [NOTE—Use peak areas where peak responses are indicated.] Separately inject equal volumes (about 2 µL) of the Standard preparation and the Assay preparation into the gas chromatograph, record the chromatograms, and measure the responses of the major peaks. Calculate the quantity, in mg, of chloroxylenol (C8H9ClO) in the portion of Chloroxylenol taken by the formula: in which C is the concentration, in mg per mL, of USP Chloroxylenol RS in the Standard preparation; and RU and RS are the ratios of the response of the chloroxylenol peak to that of the p-chlorophenol peak obtained from the Assay preparation and the Standard preparation, respectively.