Limit of acrylic acid—
pH 3.0 phosphate buffer—
Prepare 0.01 M monobasic potassium phosphate, and adjust with phosphoric acid to a pH of 3.0 ± 0.5.
Mobile phase—
Prepare a degassed solution consisting of pH 3.0 phosphate buffer and methanol (8:2).
Standard solution—
Dissolve an accurately weighed quantity of acrylic acid in water to obtain a solution containing 1.0 mg per mL. Dilute quantitatively, and stepwise if necessary, with a 2.5% alum solution to obtain a solution having a known concentration of about 30 µg per mL.
Test solution—
Transfer about 0.1 g of Polycarbophil into a vial. Add 20 mL of a 2.5% alum solution and mix. Heat at 50
for 20 minutes, then shake for 1 hour, centrifuge, and filter.
Chromatographic system
(see
Chromatography 
621
)—The liquid chromatograph is equipped with a 210-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 2.0 mL per minute. Chromatograph the
Standard solution, and record peak responses as directed for
Procedure: the relative standard deviation for replicate injections of the
Standard solution is not more than 5.0%, and the tailing factor is not more than 2.5.
Procedure—
Separately inject equal volumes (about 20 µL) of the
Standard solution and the
Test solution into the chromatograph, record the chromatograms, and measure the response for the acrylic acid peak. Calculate the percentage of acrylic acid in the portion of Polycarbophil taken by the formula:
(0.002C / W)(rU / rS),
in which
C is the concentration, in µg per mL, of acrylic acid,
W is the weight, in g, of Polycarbophil taken, and
rU and
rS are the acrylic acid peak responses obtained from the
Test solution and the
Standard solution, respectively: not more than 0.3% acrylic acid is found.
Limit of ethyl acetate—
Internal standard solution—
Dissolve an accurately weighed quantity of methyl ethyl ketone in methanol, and dilute quantitatively, and stepwise if necessary, to obtain a solution having a known concentration of about 0.075 mg per mL.
Standard solution—
Dissolve 0.225 mg, accurately weighed, of ethyl acetate into a 10-mL volumetric flask. Add 2.0 mL of the Internal standard solution, dilute with methanol to volume, and mix.
Test solution—
Transfer about 50 mg of Polycarbophil into a 10-mL volumetric flask. Add 2.0 mL of the Internal standard solution, dilute with methanol to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The gas chromatograph is equipped with a flame-ionization detector and a 10-ft. × 2-mm column that contains 1% liquid phase G25 on support S12. The column is maintained at about 160
, and the injection port and detector block are maintained at about 250
. The carrier gas is dry helium flowing at a rate of about 30 mL per minute. Chromatograph the
Standard solution, and record the chromatogram as directed for
Procedure: the relative retention times are about 1.3 for ethyl acetate, and 1.0 for methyl ethyl ketone, and the relative standard deviation for replicate injections of the ethyl acetate peak is not more than 2%.
Procedure—
Separately inject equal volumes (about 2 µL) of the
Test solution and the
Standard solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of ethyl acetate in the portion of Polycarbophil taken by the formula:
(0.001C / W)(RU / RS),
in which
C is the concentration of ethyl acetate, in µg per mL,
W is the weight of Polycarbophil, in g, and
RU and
RS are the ratios of the responses of the ethyl acetate peak to the methyl ethyl ketone peak obtained from the
Test solution and the
Standard solution, respectively: not more than 0.45% is found.
