(see' til al' ka hol).
» Cetyl Alcohol contains not less than 90.0 percent of cetyl alcohol (C16H34O), the remainder consisting chiefly of related alcohols.
Packaging and storage Preserve in well-closed containers.
USP Reference standards 11
Identification The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the System suitability solution, as obtained in the Assay.
Acid value 401: not more than 2.
Iodine value 401: not more than 5.
Hydroxyl value Place about 2 g, accurately weighed, in a dry, glass-stoppered, 250-mL flask, and add 2 mL of pyridine, followed by 10 mL of toluene. To the mixture add 10.0 mL of a solution of acetyl chloride, prepared by mixing 10 mL of acetyl chloride with 90 mL of toluene. Insert the stopper in the flask, and immerse in a water bath heated at 60 to 65 for 20 minutes. Add 25 mL of water, again insert the stopper in the flask, and shake vigorously for several minutes to decompose the excess acetyl chloride. Add 0.5 mL of phenolphthalein TS, and titrate to a permanent pink endpoint with 1 N sodium hydroxide VS, shaking the flask vigorously toward the end of the titration to maintain the contents in an emulsified condition. Perform a blank test with the same quantities of the same reagents and in the same manner. The difference between the number of mL of 1 N sodium hydroxide consumed in the test with the sample and that consumed in the blank test, multiplied by 56.1, and the result divided by the weight, in g, of the Cetyl Alcohol used, represents the hydroxyl value of the Cetyl Alcohol, which is between 218 and 238.
System suitability solution Dissolve accurately weighed quantities of USP Cetyl Alcohol RS and USP Stearyl Alcohol RS in dehydrated alcohol to obtain a solution having known concentrations of about 9 mg per mL and 1 mg per mL, respectively.
Assay preparation Dissolve 100 mg of Cetyl Alcohol in 10.0 mL of dehydrated alcohol, and mix.
Chromatographic system (see Chromatography 621) The gas chromatograph is equipped with a flame-ionization detector and a 3-mm × 2-m column packed with 10% liquid phase G2 on support S1A. The carrier gas is helium. The column temperature is maintained at about 205, the injection port temperature is maintained at about 275, and the detector temperature is maintained at about 250. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between cetyl alcohol and stearyl alcohol is not less than 4.0; and the relative standard deviation for replicate injections, calculated with the area ratio of cetyl alcohol to stearyl alcohol, is not more than 1.5%.
Procedure Inject about 2 µL of the Assay preparation into the chromatograph, record the chromatogram, and measure the areas for the major peaks. Calculate the percentage of C16H34O in the portion of Cetyl Alcohol taken by the formula:
100(rU / rs)in which rU is the peak area for cetyl alcohol obtained from the Assay preparation; and rs is the sum of the areas of all the peaks except the solvent peak.
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USP35NF30 Page 1752Pharmacopeial Forum: Volume No. 31(2) Page 494