Identification—
Transfer the contents of 1 tube of Ophthalmic Ointment to a 100-mL beaker, add about 25 mL of alcohol, and stir by mechanical means for about 15 minutes. Filter, and use the clear solution as the
Test preparation. Prepare Standard solutions in alcohol containing 0.7 mg per mL of
USP Prednisolone Acetate RS and 14 mg per mL of
USP Sulfacetamide Sodium RS. Apply separately 10 µL of the
Test preparation and 10 µL of each Standard solution to a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Position the plate in a chromatographic chamber, and develop the chromatograms in a solvent system consisting of a mixture of chloroform, heptane, alcohol, and water (50:50:50:2) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and allow the solvent to evaporate. Examine the plate under UV light: the
Test preparation exhibits two spots whose
RF values and intensities correspond to the respective spots from the Standard solutions.
Assay for sulfacetamide sodium—
Mobile phase—
Prepare a filtered and degassed mixture of water, methanol, and glacial acetic acid (890:100:10). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Transfer about 50 mg of
USP Sulfacetamide Sodium RS, accurately weighed, to a 40-mL centrifuge tube. Add 10.0 mL of dilute methanol (1 in 5), insert the stopper in the tube, and mix, using a vortex mixer for about 3 minutes to dissolve the standard. Add 7.5 mL of heptane, insert the stopper in the tube, and mix, using a vortex mixer for another 3 minutes. Centrifuge to effect separation of the phases. Withdraw and discard the upper, heptane layer. Transfer 3.0 mL of the bottom layer to a 500-mL volumetric flask, add dilute methanol (1 in 5) to volume, and mix.
Assay preparation—
Transfer an accurately weighed quantity of Ophthalmic Ointment, equivalent to about 100 mg of sulfacetamide sodium, to a 40-mL centrifuge tube. Add 15.0 mL of heptane, insert the stopper in the tube, and mix, using a vortex mixer for about 3 minutes to dissolve the Ointment. Add 20.0 mL of dilute methanol (1 in 5), insert the stopper in the tube, and mix, using a vortex mixer for 3 minutes. Centrifuge to effect separation of the phases. Withdraw and discard the upper, heptane layer. Transfer 3.0 mL of the bottom layer into a 500-mL volumetric flask, add dilute methanol (1 in 5) to volume, and mix.
System suitability preparation—
Dissolve 3 mg of sulfanilamide in 100 mL of the Standard preparation, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 25-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard preparation and the
System suitability preparation, and record the peak responses as directed for
Procedure: the column efficiency determined for the analyte peak is not less than 1500 theoretical plates, the resolution,
R, between the sulfacetamide and sulfanilamide peaks is not less than 3, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 90 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C
8H
9N
2NaO
3S·H
2O in the portion of Ophthalmic Ointment taken by the formula:
3.33(254.24 / 236.23)C(rU / rS),
in which 254.24 and 236.23 are the molecular weights of sulfacetamide sodium monohydrate and anhydrous sulfacetamide sodium, respectively,
C is the concentration, in µg per mL, calculated on the anhydrous basis, of
USP Sulfacetamide Sodium RS in the
Standard preparation, and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
Assay for prednisolone acetate—
Mobile phase—
Prepare a filtered and degassed mixture of water and acetonitrile (60:40). Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Internal standard solution—
Transfer about 70 mg of norethindrone to a 100-mL volumetric flask, add dilute methanol (9 in 10) to volume, and mix.
Standard preparation—
Transfer about 20 mg of
USP Prednisolone Acetate RS, accurately weighed, to a 25-mL volumetric flask, add dilute methanol (9 in 10) to volume, and mix. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, add 5.0 mL of
Internal standard solution, add dilute methanol (9 in 10) to volume, and mix.
Assay preparation—
Transfer an accurately weighed quantity of Ophthalmic Ointment, equivalent to about 4 mg of prednisolone acetate, to a 50-mL centrifuge tube. Add 10.0 mL of heptane, and mix, using a vortex mixer for about 2 minutes to dissolve the Ointment. Add 5.0 mL of Internal standard solution and 20.0 mL of dilute methanol (9 in 10), and mix, using a vortex mixer for 2 minutes. Centrifuge to effect separation of the phases. Withdraw and discard the upper, heptane layer. Transfer the lower layer to a 100-mL volumetric flask. Add dilute methanol (9 in 10) to volume, and mix to obtain the Assay preparation.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency determined from the analyte peak is not less than 3000, the tailing factor for the analyte peak is not more than 2.5, the resolution,
R, between the analyte and internal standard peaks is not less than 4.5, and the relative standard deviation for replicate injections is not more than 1.5%.
Procedure—
Separately inject equal volumes (about 40 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 1.0 for prednisolone acetate and 1.5 for norethindrone. Calculate the quantity, in mg, of C
23H
30O
6 in the portion of the Ophthalmic Ointment taken by the formula:
100C(RU / RS),
in which
C is the concentration, in mg per mL, of
USP Prednisolone Acetate RS in the
Standard preparation taken; and
RU and
RS are the peak response ratios obtained from the
Assay preparation and the
Standard preparation, respectively.
