Chromatographic system
(see
Chromatography 621)The liquid chromatograph is equipped with a 281-nm detector and a 4.6-mm × 25-cm column that contains 5-µm packing L11 and is maintained at a constant temperature of about 30
. Adjust the flow rate to obtain a retention time of about 20 minutes for the main capsaicin peak. Chromatograph the
Standard capsaicin solution, and record the peak responses as directed for
Procedure: the relative standard deviation for replicate injections is not more than 2%.
Procedure
Separately inject equal volumes (about 20 µL) of the
Standard capsaicin solution, the
Standard dihydrocapsaicin solution, and the
Test solution into the chromatograph, record the chromatogram for a period of time that is twice that of the retention time of capsaicin, and measure the areas of the responses for all of the peaks. Calculate the percentage of capsaicin (C
18H
27NO
3) in the portion of Capsaicin taken by the formula:
25,000(C / W)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Capsaicin RS in the
Standard capsaicin solution;
W is the weight, in mg, of Capsaicin taken to prepare the
Test solution; and
rU and
rS are the capsaicin peak responses obtained from the
Test solution and the
Standard capsaicin solution, respectively. Not less than 55% is found. Calculate the percentage of dihydrocapsaicin (C
18H
29NO
3) in the portion of Capsaicin taken by the formula:
25,000(C / W)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Dihydrocapsaicin RS in the
Standard dihydrocapsaicin solution;
W is the weight, in mg, of Capsaicin taken to prepare the
Test solution; and
rU and
rS are the dihydrocapsaicin peak responses obtained from the
Test solution and the
Standard dihydrocapsaicin solution, respectively. The sum of the percentage of capsaicin found and of the percentage of dihydrocapsaicin found is not less than 75%. Using the chromatograms obtained from the
Standard capsaicin solution and the
Test solution, calculate the percentage of other capsaicinoids in the portion of Capsaicin taken by the formula:
25,000(C / W)(rT / rS),
in which
C is the concentration, in mg per mL, of
USP Capsaicin RS in the
Standard capsaicin solution;
W is the weight, in mg, of Capsaicin taken to prepare the
Test solution;
rT is the sum of the peak responses of the capsaicinoids other than capsaicin and dihydrocapsaicin in the chromatogram obtained from the
Test solution; and
rS is the capsaicin peak response obtained from the
Standard capsaicin solution. Not more than 15% of other capsaicinoids is found.