Mobile phase and Chromatographic system—Proceed as directed in the Assayunder Chloramphenicol.

Standard preparation— Transfer about 25mg of USP Chloramphenicol RS,accurately weighed,to a 100-mLvolumetric flask,dissolve in methanol,dilute with methanol to volume,and mix.Transfer 10.0mLof the resulting solution to a 25-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Filter a portion of this solution through a 0.5-µm or finer porosity filter,and use the clear filtrate as the Standard preparation.

Assay preparation— Transfer an accurately weighed quantity of Ophthalmic Ointment,equivalent to about 25mg of chloramphenicol,to a suitable conical flask,add 20mLof cyclohexane,mix,and sonicate for about 2minutes.Add 60mLof methanol,and mix.Filter this mixture,collecting the filtrate in a 100-mLvolumetric flask.Wash the filter with methanol,collecting the washings in the volumetric flask.Dilute with methanol to volume,and mix.Transfer 50.0mLof the resulting solution to a suitable round-bottom flask,and evaporate to dryness by rotating the flask under vacuum in a water bath at 35.Dissolve the residue in 50.0mLof methanol.Transfer 10.0mLof the resulting solution to a 25-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.Filter a portion of this solution through a 0.5-µm or finer porosity filter,and use the clear filtrate as the Assay preparation.

Procedure— Proceed as directed for Procedurein the Assayunder Chloramphenicol.Calculate the quantity,in mg,of C11H12Cl2N2O5in the portion of Ophthalmic Ointment taken by the formula: in which the terms are as defined therein.