Assay for oxytetracycline—
Transfer an accurately measured volume of Ophthalmic Suspension to a separator, add 50 mL of ether, and shake. Add 25 mL of 0.1 N hydrochloric acid, shake, and allow to separate. Collect the acid layer, and repeat the extraction with three additional 25-mL portions of 0.1 N hydrochloric acid. Combine the acid extracts in a 200-mL volumetric flask, dilute with 0.1 N hydrochloric acid to volume, and mix. Proceed as directed for oxytetracycline under
Antibiotics—Microbial Assays 
81
, using an accurately measured volume of this solution diluted quantitatively and stepwise with water to obtain a
Test Dilution having a concentration assumed to be equal to the median dose level of the Standard.
Assay for hydrocortisone acetate—
Mobile phase—
Prepare a degassed and filtered mixture of water and methanol (50:50).
Standard preparation—
Dissolve an accurately weighed quantity of
USP Hydrocortisone Acetate RS in a mixture of
Mobile phase and alcohol (80:20) to obtain a solution having a known concentration of about 0.06 mg per mL.
Assay preparation—
Transfer an accurately measured volume of Ophthalmic Suspension, equivalent to about 30 mg of hydrocortisone acetate, to a separator containing 25 mL of pH 9.0 alkaline borate buffer (see under
Buffer Solutions in the section
Reagents, Indicators, and Solutions). Extract with four 25-mL portions of chloroform, filtering each chloroform extract through a thin layer of chloroform-washed anhydrous sodium sulfate into a 250-mL volumetric flask. Rinse the sodium sulfate with chloroform, collecting the filtrate in the volumetric flask, dilute with chloroform to volume, and mix. Transfer 25.0 mL of the resulting solution to a 50-mL conical flask, and evaporate slowly with the aid of mild heat until about 5 mL remains. Add about 15 mL of alcohol, and evaporate slowly until about 5 mL remains. Transfer this solution to a 50-mL volumetric flask, dilute with a mixture of
Mobile phase and alcohol (80:20) to volume, and mix.
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 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 235 theoretical plates, the tailing factor for the analyte peak is not more than 1.7, and the relative standard deviation of replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 25 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
23H
32O
6 in each mL of the Ophthalmic Suspension taken by the formula:
500(C / V)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Hydrocortisone Acetate RS in the
Standard preparation; V is the volume, in mL, of Ophthalmic Suspension taken; and
rU and
rS are the peak responses obtained from the
Assay preparation and the
Standard preparation, respectively.
