A: Place 1drop of Oral Solution on a thin-layer chromatographic plate coated with a 0.25-mm layer of chromatographic silica gel.Spray the plate with 3.5%phosphomolybdic acid solution (prepared by dissolving 3.5g of phosphomolybdic acid in 100mLof isopropyl alcohol),and immediately heat the plate over a hot plate:a dark blue spot appears on a yellow background.

B: The retention time of the major peak in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of the Standard preparation,as obtained in the Assay.

FOR ORAL SOLUTION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.

FOR ORAL SOLUTION PACKAGED IN MULTIPLE-UNIT CONTAINERS:

Mobile phase,Standard preparation,System suitability preparation,and Chromatographic system— Prepare as directed in the Assayunder Dihydrotachysterol.

Assay preparation [FOR ORAL SOLUTION IN AN OIL MEDIUM]—Transfer an accurately measured volume of Oral Solution,equivalent to about 500µg of dihydrotachysterol,by means of a “to contain”pipet to a 50-mLvolumetric flask.Rinse the pipet with Mobile phase,add the rinsing to the flask,dilute with Mobile phaseto volume,and mix.

Assay preparation[FOR ORAL SOLUTION IN AN AQUEOUS MEDIUM]— Transfer an accurately measured volume of Oral Solution,equivalent to about 600µg of dihydrotachysterol,to a separator containing about 30mLof water.Add about 1g of sodium chloride,mix,and extract with three 15-mLportions of chloroform,filtering each portion through absorbent cotton into a suitable glass-stoppered conical flask.Wash the cotton with about 5mLof chloroform,collecting the washing in the glass-stoppered conical flask.Evaporate the chloroform extracts,and wash with the aid of a current of air to dryness.Dissolve the residue in 50.0mLof Mobile phase,and mix.

Procedure— Proceed as directed for Procedurein the Assayunder Dihydrotachysterol.Calculate the quantity,in µg,of dihydrotachysterol (C28H46O)in the volume of Oral Solution taken by the formula: in which Cis the concentration,in µg per mL,of USP Dihydrotachysterol RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.