Identification—
To an accurately weighed quantity of it, equivalent to about 100 mg of decoquinate, add 40 mL of chloroform, and heat under a reflux condenser on a water bath for 20 minutes, cool, and filter. Use the filtrate as the test solution. Apply 10-µL portions of the test solution and of a Standard solution in chloroform containing 2.5 mg of
USP Decoquinate RS per mL to the starting line of a suitable thin-layer chromatographic plate (see
Chromatography 
621
) coated with a 0.25-mm layer of chromatographic silica gel mixture. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of chloroform and alcohol (70:30) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, and allow to dry in a current of air. Locate the spots under short-wavelength UV light: the
RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.
Assay—
Extract an accurately weighed quantity of Premix, equivalent to about 200 mg of decoquinate, with 50 mL of chloroform in a small continuous extraction apparatus for 8 reflux cycles. Transfer the extract to a 100-mL volumetric flask with the aid of chloroform, cool, dilute with chloroform to volume, and mix. Transfer 5.0 mL of this solution to a second 100-mL volumetric flask, dilute with dehydrated alcohol to volume, and mix. Transfer 5.0 mL of this solution to a third 100-mL volumetric flask, add 10 mL of 0.1 N hydrochloric acid, dilute with dehydrated alcohol to volume, and mix (
Assay preparation). Transfer 50 mg of
USP Decoquinate RS, accurately weighed, to a 100-mL volumetric flask, add 10 mL of hot chloroform, swirl to dissolve, and while still warm slowly add 70 mL of dehydrated alcohol. Allow to cool, dilute with dehydrated alcohol to volume, and mix. Immediately transfer 10.0 mL of this solution to a second 100-mL volumetric flask, dilute with dehydrated alcohol to volume, and mix. Transfer 10.0 mL of this solution to a third 100-mL volumetric flask, add 10 mL of 0.1 N hydrochloric acid, dilute with dehydrated alcohol to volume, and mix. This
Standard preparation contains about 0.005 mg of
USP Decoquinate RS per mL. Concomitantly determine the absorbances of the
Standard preparation and the
Assay preparation at the wavelength of maximum absorbance at about 265 nm, with a spectrophotometer, using a mixture of dehydrated alcohol, 0.1 N hydrochloric acid, and chloroform (90:10:0.25) as the blank. Calculate the percentage of C
24H
35NO
5 in the portion of Premix taken by the formula:
4000(C / W)(AU / AS),
in which
C is the concentration, in mg per mL, of
USP Decoquinate RS in the
Standard preparation; W is the quantity, in g, of Premix taken to prepare the
Assay preparation; and
AU and
AS are the absorbances of the
Assay preparation and the
Standard preparation, respectively.
