Identification—
Tablets meet the requirement of the
Thin-layer Chromatographic Identification Test 
201
, the test solution being the filtrate obtained by shaking a quantity of powdered Tablets, equivalent to about 200 mg of azathioprine, with 10 mL of 6 N ammonium hydroxide, the Standard solution being a solution of
USP Azathioprine RS in 6 N ammonium hydroxide containing 20 mg per mL, and 5-µL portions of each solution being spotted on a thin-layer chromatographic plate coated with a 0.25-mm layer of microcrystalline cellulose, and butyl alcohol, previously saturated with 6 N ammonium hydroxide, being used for developing.
Dissolution 711—
Medium:
water; 900 mL.
Apparatus 2:
50 rpm.
Time:
30 minutes.
Procedure—
Determine the amount of C
9H
7N
7O
2S dissolved from UV absorbances at the wavelength of maximum absorbance at about 280 nm of filtered portions of the solution under test, suitably diluted with
Medium, if necessary, in comparison with a Standard solution having a known concentration of
USP Azathioprine RS in the same medium.
Tolerances—
Not less than 75% (Q) of the labeled amount of C9H7N7O2S is dissolved in 30 minutes.
Assay—
Mobile phase—
Dissolve 1.1 g of sodium 1-heptanesulfonate in 700 mL of water, add 300 mL of methanol, and mix. Adjust the solution with 1 N hydrochloric acid to a pH of 3.5. Filter the solution through a 0.8-µm solvent-resistant membrane, and degas, making adjustments if necessary (see
System Suitability under
Chromatography 621).
Standard preparation—
Transfer about 25 mg of
USP Azathioprine RS, accurately weighed, to a 50-mL volumetric flask. Add about 15 mL of methanol and 0.5 mL of ammonium hydroxide to the flask, swirl, and sonicate for 2 minutes. Dilute with methanol to volume, and mix. Transfer 10.0 mL of this solution to a 50-mL volumetric flask, dilute with water to volume, and mix.
Assay preparation—
Weigh and finely powder not fewer than 20 Tablets. Accurately weigh a portion of the powder, equivalent to about 50 mg of azathioprine, and transfer to a 100-mL volumetric flask. Add 25 mL of methanol and 1.0 mL of ammonium hydroxide to the flask, swirl, and sonicate for 2 minutes. Dilute with methanol to volume, and mix. Allow the excipients to settle, transfer 10.0 mL of the supernatant to a 50-mL volumetric flask, dilute with water to volume, and mix.
Chromatographic system
(see
Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the column efficiency is not less than 800 theoretical plates, the tailing factor for the azathioprine peak is not more than 1.5, and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure—
Separately inject equal volumes (about 10 µL) of the
Standard preparation and the
Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of azathioprine (C
9H
7N
7O
2S) in the portion of Tablets taken by the formula:
500(C)(rU / rS),
in which
C is the concentration, in mg per mL, of
USP Azathioprine RS in the
Standard preparation, and
rU and
rS are the peak responses for azathioprine obtained from the
Assay preparation and the
Standard preparation, respectively.
