Identification—
Extract a quantity of finely powdered Tablets, equivalent to about 50 mg of allopurinol, by trituration with 10 mL of 0.1 N sodium hydroxide. Filter, acidify the filtrate with 1 N acetic acid, collect the precipitated allopurinol (allow 10 to 15 minutes for sufficient precipitation to occur), wash the precipitate with 3 mL of dehydrated alcohol, in portions, and finally wash with 4 mL of anhydrous ethyl ether. Allow to dry in air for 15 minutes, then dry at 105
for 3 hours: the residue so obtained meets the requirements for the
Identification test under
Allopurinol.
Dissolution 
711
—
Medium:
0.01 N hydrochloric acid; 900 mL.
Apparatus 2:
75 rpm.
Time:
45 minutes.
Standard stock solution—
Prepare a stock solution by transferring about 40 mg of
USP Allopurinol RS, accurately weighed, to a 200-mL volumetric flask. Add 10 mL of 0.1 N sodium hydroxide, sonicate for about 2 minutes, shake by mechanical means for about 10 minutes, dilute with
Dissolution Medium to volume, and mix.
Standard solution—
Dilute the Standard stock solution with Dissolution Medium to obtain a solution having a concentration similar to that expected in the solution under test.
Procedure—
Determine the amount of C5H4N4O dissolved by employing UV absorption at the wavelength of maximum absorbance at about 250 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, in comparison with the Standard solution.
Tolerances—
Not less than 75% (Q) of the labeled amount of C5H4N4O is dissolved in 45 minutes.
Assay—
[NOTE—Do not allow the
Mobile phase to remain in the column overnight. After performing the procedure, flush the system with water for not less than 20 minutes, and then flush with methanol for 20 minutes.
]
Mobile phase—
Prepare a filtered and degassed 0.05 M solution of monobasic ammonium phosphate.
Internal standard solution—
On the day of use, dissolve about 50 mg of hypoxanthine in 10 mL of 0.1 N sodium hydroxide, shake by mechanical means until dissolved (about 10 minutes), dilute with water to 50 mL, and mix.
Standard preparation—
On the day of use, transfer about 50 mg of
USP Allopurinol RS, accurately weighed, to a 50-mL volumetric flask, add 10 mL of 0.1 N sodium hydroxide, shake by mechanical means for 10 minutes, dilute with water to volume, and mix. Transfer 4.0 mL of this solution and 2.0 mL of
Internal standard solution to a 200-mL volumetric flask, dilute with
Mobile phase to volume, and mix.
Assay preparation—
Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 50 mg of allopurinol, to a 50-mL volumetric flask, add 10 mL of 0.1 N sodium hydroxide, shake by mechanical means for 10 minutes, add water to volume, and mix. [NOTE—From this point, conduct the remainder of the Assay without delay.] Filter, rejecting the first 10 mL of the filtrate. Transfer 4.0 mL of the filtrate and 2.0 mL of Internal standard solution to a 200-mL volumetric flask, dilute with Mobile phase 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 1.5 mL per minute. Chromatograph the
Standard preparation, and record the peak responses as directed for
Procedure: the relative retention times are about 0.6 for hypoxanthine and 1.0 for allopurinol; the resolution,
R, between the analyte and internal standard is not less than 5; and the relative standard deviation for replicate injections is not more than 3.0%.
Procedure—
Separately inject equal volumes (about 15 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 allopurinol (C
5H
4N
4O) in the portion of Tablets taken by the formula:
2.5C(RU / RS),
in which
C is the concentration, in µg per mL, of
USP Allopurinol RS in the
Standard preparation; and
RU and
RS are the peak response ratios of allopurinol to hypoxanthine obtained from the
Assay preparation and the
Standard preparation, respectively.
