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C5H4N4S·H2O 170.19

6H-Purine-6-thione, 1,7-dihydro-, monohydrate.
Purine-6-thiol monohydrate [6112-76-1].

Anhydrous 152.18 [50-44-2].
»Mercaptopurine contains not less than 97.0 percent and not more than 102.0 percent of C5H4N4S, calculated on the anhydrous basis.
Packaging and storage— Preserve in well-closed containers.
A: Ultraviolet Absorption 197U
Solution: 5 µg per mL.
Medium: 0.1 N hydrochloric acid.
Absorptivities at 325 nm, calculated on the anhydrous basis, do not differ by more than 3.0%. The ratio A255/A325 does not exceed 0.06.
B: To a solution of 600 mg in 6 mL of sodium hydroxide solution (1 in 33) add slowly, with shaking, 0.5 mL of methyl iodide. Allow the mixture to stand for 2 hours at room temperature, cool in an ice bath, and adjust with acetic acid to a pH of about 5. Collect the crystals, and recrystallize from hot water: the methylmercaptopurine trihydrate so obtained, dried at 120 for 30 minutes, melts between 218 and 222, with decomposition.
Water, Method I 921: not more than 12.0%.
Phosphorus— Digest 200 mg with 2 mL of 15 N sulfuric acid in a large test tube, periodically adding nitric acid, dropwise and with caution. Continue heating until practically all of the liquid has evaporated and the residue is colorless. Transfer the residue, with the aid of small portions of water, to a 25-mL volumetric flask, add 1 mL of 15 N sulfuric acid, 0.5 mL of nitric acid, 0.75 mL of ammonium molybdate TS, and 1 mL of aminonaphtholsulfonic acid TS, then dilute with water to volume, and mix. Allow to stand for 5 minutes, and determine the absorbance of this solution at 750 nm, with a suitable spectrophotometer, using as a blank a solution of the same quantities of the same reagents, prepared in the same manner. The absorbance of this solution is not greater than that of a solution obtained by treating as directed above, beginning with “add 1 mL of 15 N sulfuric acid,” a 2-mL portion of a standard phosphate solution prepared to contain, in each mL, 43.96 µg of dried monobasic potassium phosphate, equivalent to 10 µg of P (0.010%).
Assay— Dissolve about 300 mg of Mercaptopurine, accurately weighed, in 80 mL of dimethylformamide. Add 5 drops of a 1 in 100 solution of thymol blue in dimethylformamide, and titrate with 0.1 N sodium methoxide VS, using a magnetic stirrer and taking precautions against absorption of atmospheric carbon dioxide. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N sodium methoxide is equivalent to 15.22 mg of C5H4N4S.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Feiwen Mao, M.S.
(MDOOD05) Monograph Development-Ophthalmics Oncologics and Dermatologicals
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 2890
Chromatographic Column—
Chromatographic columns text is not derived from, and not part of, USP 32 or NF 27.