Identification—
The retention time of the major peak in the chromatogram of the
Assay preparation corresponds to that of the major peak in the chromatogram of the
System suitability solution, as obtained in the
Assay.
Assay—
System suitability solution—
Dissolve accurately weighed quantities of
USP Octyldodecanol RS and
USP Stearyl Alcohol RS in alcohol to obtain a solution having known concentrations of about 9 mg per mL and 1 mg per mL, respectively.
Assay preparation—
Dissolve 90 mg of Octyldodecanol in 10.0 mL of alcohol, and mix.
Chromatographic system
(see
Chromatography 
621
)—The gas chromatograph is equipped with a flame-ionization detector and a 2-mm × 2-m column packed with 3% liquid phase G2 on support S1A. The carrier gas is nitrogen. The column temperature is programmed as follows. Initially it is equilibrated at about 80
, then increased at a rate of 6
per minute to 300
. The detector and the injection port temperatures are both maintained at about 280
. Chromatograph the
System suitability solution, and record the peak responses as directed for
Procedure: the resolution,
R, between octyldodecanol and stearyl alcohol is not less than 4.0; and the relative standard deviation for replicate injections 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 C
20H
42O in the portion of Octyldodecanol taken by the formula:
100(rU / rs),
in which
rU is the peak area for octyldodecanol obtained from the
Assay preparation; and
rs is the sum of the areas of all the peaks except the solvent peak.
