Identification—
The UV absorption spectrum of the
Acidic assay preparation employed for measurement of absorbance in the
Assay exhibits maxima and minima at the same wavelengths as that of a similar solution of
USP Thioguanine RS, concomitantly measured.
Dissolution 
711
—
Medium:
water; 900 mL.
Apparatus 2:
50 rpm.
Time:
45 minutes.
Standard preparation—
Dissolve an accurately weighed quantity of
USP Thioguanine RS in 1 N sodium hydroxide to obtain a solution having a known concentration of about 4.5 µg per mL.
Procedure—
Determine the amount of C5H5N5S dissolved from UV absorbances at the wavelength of maximum absorbance at about 348 nm of filtered portions of the solution under test, suitably diluted with 0.1 N hydrochloric acid, in comparison with the Standard preparation.
Tolerances—
Not less than 75% (Q) of the labeled amount of C5H5N5S is dissolved in 45 minutes.
Assay—
Standard preparations—
Dissolve an accurately weighed quantity of
USP Thioguanine RS in sodium hydroxide solution (1 in 250), and dilute quantitatively and stepwise with the sodium hydroxide solution to obtain a
Standard preparation having a known concentration of 80 µg per mL. Transfer 5.0 mL of this solution to a 100-mL volumetric flask, add dilute hydrochloric acid (1 in 10) to volume, and mix, to obtain the
Acidic standard preparation. Transfer another 5.0-mL portion of the solution to a second 100-mL volumetric flask, add 10.0 mL of 1 N sodium hydroxide, dilute with water to volume, and mix, to obtain the
Basic standard preparation.
Assay preparations—
Weigh and finely powder not less than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 40 mg of thioguanine, to a 500-mL volumetric flask, add 50 mL of 1 N sodium hydroxide, and allow to stand for 10 minutes, with frequent swirling. Dilute with water to volume, mix, and filter a portion of the solution through a pledget of glass wool. Transfer 5.0 mL of the filtrate to a 100-mL volumetric flask, add dilute hydrochloric acid (1 in 10) to volume, and mix, to obtain the Acidic assay preparation. Transfer another 5.0-mL portion of the filtrate to a second 100-mL volumetric flask, add 10.0 mL of 1 N sodium hydroxide, dilute with water to volume, and mix, to obtain the Basic assay preparation.
Procedure—
Concomitantly determine the absorbances of the
Acidic assay preparation and the
Acidic standard preparation in 1-cm cells at the wavelength of maximum absorbance at about 348 nm, with a suitable spectrophotometer, using the
Basic assay preparation and the
Basic standard preparation, respectively, as the blanks. Calculate the quantity, in mg, of C
5H
5N
5S in the portion of Tablets taken by the formula:
10C(AU / AS),
in which
C is the concentration, in µg per mL, of
USP Thioguanine RS in the
Acidic standard preparation, and
AU and
AS are the absorbances of the
Acidic assay preparation and the
Acidic standard preparation, respectively.
