Standard Preparation
Place 100 mg of
USP Methylparaben RS and 10 mg of
USP Propylparaben RS, each accurately weighed, in a 200-mL volumetric flask, dilute with
Internal Standard Solution to volume, and mix. Place 10 mL of this solution in a 25-mL conical flask, and proceed as directed for
Test Preparation, beginning with Add 3 mL of pyridine.
Procedure
Separately inject equal volumes (2 µL) of the silanized solution from the
Standard Preparation and the
Test Preparation into the chromatograph, record the chromatograms with the apparatus adjusted to the parameters set forth in the accompanying table, and measure the areas under the peaks for methylparaben, propylparaben, and benzophenone. Calculate the content, in µg per mL, of methylparaben (C
8H
8O
3) in the sample under test by the formula:
10(CM / V)(p1 / p3)(P3 / P1)
in which
CM is the concentration, in µg per mL, of methylparaben in the
Standard Preparation; V is the volume, in mL, of the specimen taken;
p1 and
p3 are the peak areas for methylparaben and benzophenone, respectively, obtained from the
Test Preparation; and
P1 and
P3 are the peak areas of methylparaben and benzophenone, respectively, obtained from the
Standard Preparation. Similarly, calculate the content, in µg per mL, of propylparaben (C
10H
12O
3) in the specimen under test by the formula:
10(CP / V)(p2 / p3)(P3 / P2)
in which
CP is the concentration, in µg per mL, of propylparaben in the
Standard Preparation; V is the volume, in mL, of the specimen taken;
p2 and
p3 are the peak areas for propylparaben and benzophenone, respectively, obtained from the
Test Preparation; and
P2 and
P3 are the peak areas of propylparaben and benzophenone, respectively, obtained from the
Standard Preparation.
Ethylparaben and butylparaben may be determined in a similar manner.