Standard preparation
Dissolve a suitable quantity of
USP Deslanoside RS in alcohol, and quantitatively dilute with alcohol to obtain a solution having a known concentration of about 200 µg per mL.
Procedure
Transfer 3.0 mL each of the
Standard preparation, the
Assay preparation, and alcohol to provide the blank, to separate 25-mL conical flasks. Evaporate each with gentle warming and with the aid of a current of air just to dryness, and cool in a vacuum desiccator for 30 minutes. Add 15.0 mL of acid-ferric chloride TS to each flask, mix by swirling, and allow the mixtures to stand protected from light, swirling frequently, at a temperature not exceeding 30
, for 15 minutes. Pass each through separate fine glass wool filters. Concomitantly determine the absorbances of the solutions in 1-cm cells at the wavelength of maximum absorbance at about 590 nm, with a suitable spectrophotometer, using the blank to set the instrument. Repeat the measurements at 2-minute intervals until maximum absorbance readings have been obtained. Calculate the quantity, in mg, of C
47H
74O
19 in the Deslanoside taken by the formula:
0.1C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Deslanoside RS in the
Standard preparation; and
AU and
AS are the maximum absorbances of the solutions from the
Assay preparation and the
Standard preparation, respectively.