Identification—
A:
The UV absorption spectrum of the solution of Tablets employed for measurement of absorbance in the Assay exhibits a maximum at 325 ± 2 nm, and the ratio A255 / A325 does not exceed 0.09.
B:
Triturate a quantity of finely powdered Tablets, equivalent to about 600 mg of mercaptopurine, with three 25-mL portions of hot alcohol. Filter the hot alcohol extracts, and evaporate the filtrate on a steam bath to dryness. Add to the residue 5 mL of sodium hydroxide solution (1 in 33), agitate well, and filter: the clear filtrate so obtained responds to
Identification test
B under
Mercaptopurine.
Dissolution 
711
—
TEST 1—
Medium:
0.1 N hydrochloric acid; 900 mL.
Apparatus 2:
50 rpm.
Time:
60 minutes.
Determine the amount of mercaptopurine (C5H4N4S) dissolved by employing the following method.
Mobile phase—
Prepare a filtered and degassed solution of 0.1% acetic acid in water. Make adjustments if necessary (see
System Suitability under
Chromatography 621).
Chromatographic system (see Chromatography 621)—
The liquid chromatograph is equipped with a 230-nm detector and a 3.9-mm × 15-cm column that contains packing L1. The flow rate is about 2.5 mL per minute. Chromatograph replicate injections of the Standard solution prepared as described below for
Procedure, and record the peak responses as directed for
Procedure: the retention time for mercaptopurine is not less than 4 minutes, and the relative standard deviation is not more than 2.0%.
Procedure—
Inject a volume (about 10 µL) of a filtered portion of the solution under test into the chromatograph, record the chromatogram, and measure the response for the major peak. Calculate the quantity of C
5H
4N
4S dissolved in comparison with a Standard solution having a known concentration of
USP Mercaptopurine RS in the same
Medium and similarly chromatographed.
Tolerances—
Not less than 80% (Q) of the labeled amount of C5H4N4S is dissolved in 60 minutes.
TEST 2—
If the product complies with this test, the labeling indicates that it meets USP
Dissolution Test 2.
Medium, Apparatus, Chromatographic system, and Procedure—
Proceed as directed for Test 1.
Time:
120 minutes.
Tolerances—
Not less than 80% (Q) of the labeled amount of C5H4N4S is dissolved in 120 minutes.
Assay—
Weigh and finely powder not fewer than 20 Tablets. Accurately weigh a portion of the powder, equivalent to about 50 mg of mercaptopurine, and transfer to a 100-mL volumetric flask. Add 20 mL of water and 1.5 mL of 1 N sodium hydroxide, and swirl for not more than 5 minutes. Dilute with water to volume, mix, and filter, discarding the first 20 mL of the filtrate. Dilute an accurately measured portion of the filtrate quantitatively and stepwise with 0.1 N hydrochloric acid to give a final concentration of about 5 µg per mL. Dissolve an accurately weighed quantity of
USP Mercaptopurine RS in a mixture of 10 mL of water and 1 mL of 1 N sodium hydroxide contained in a 100-mL volumetric flask, dilute with water to volume, and mix. Dilute an aliquot of this solution quantitatively and stepwise with 0.1 N hydrochloric acid to obtain a Standard solution having a known concentration of about 5 µg per mL. Concomitantly determine the absorbances of both solutions in 1-cm cells at the wavelength of maximum absorbance at about 325 nm, with a suitable spectrophotometer, using 0.1 N hydrochloric acid as the blank. Calculate the quantity, in mg, of mercaptopurine (C
5H
4N
4S·H
2O) in the portion of Tablets taken by the formula:
(170.19/152.18)10C(AU / AS),
in which 170.19 and 152.18 are the molecular weights of mercaptopurine monohydrate and anhydrous mercaptopurine, respectively;
C is the concentration, in µg per mL, of
USP Mercaptopurine RS in the Standard solution; and
AU and
AS are the absorbances of the solution from Tablets and the Standard solution, respectively.
