A: Place an amount of powdered Tablets,equivalent to 15to 20mg of probucol,in the depression of a spot plate,and add two drops of sulfuric acid:an intense yellow color is produced immediately.The color corresponds to that obtained from a similar preparation of USP Probucol RS.

B: Transfer a quantity of finely ground Tablets,equivalent to about 1000mg of probucol,to a copper centrifuge tube.Add 5mLof methylene chloride,cap the tube,and mix for about 30seconds on a vortex mixer.Centrifuge at about 7000rpm for 10minutes.Decant the supernatant,and place about 1mLof this solution on each side of a potassium bromide plate,holding the plate at an angle so that a thin film is formed on the plate:the IRabsorption spectrum of the clear film so obtained exhibits maxima only at the same wavelengths as that of a similar preparation of USP Probucol RS.

Mobile phase,System suitability preparation,and Chromatographic system— Proceed as directed in the Assayunder Probucol.

Standard preparation— Dissolve an accurately weighed quantity of USP Probucol RSin Mobile phase,and dilute quantitatively and stepwise with Mobile phaseto obtain a solution having a known concentration of about 50µg per mL.

Assay preparation— Weigh and finely powder not less than 20Tablets.Transfer an accurately weighed quantity of the powder,equivalent to about 500mg of probucol,to a 100-mLvolumetric flask,add 80mLof Mobile phase,and stir the mixture vigorously for about 1hour.Dilute with Mobile phaseto volume,and mix.Transfer 1.0mLof this solution to a 100-mLvolumetric flask,dilute with Mobile phaseto volume,mix,and filter.

Procedure— Separately inject equal volumes (about 50µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C31H48O2S2in the portion of Tablets taken by the formula: in which Cis the concentration,in µg per mL,of USP Probucol RSin the Standard preparation,and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.