C9H7N7O2S 277.26

1H-Purine,6-[(1-methyl-4-nitro-1H-imidazol-5-yl)thio]-.
6-[(1-Methyl-4-nitroimidazol-5-yl)thio]purine [446-86-6].

Packaging and storage— Preserve in tight,light-resistant containers.

USP Reference standards á11ñ— USP Azathioprine RS.USP Mercaptopurine RS.

Identification—

Acidity or alkalinity— Shake 2.0g with 100mLof water for 15minutes,and filter:20.0mLof the filtrate requires for neutralization not more than 0.10mLof 0.020Nhydrochloric acid or not more than 0.10mLof 0.020Nsodium hydroxide,methyl red TSbeing used as the indicator.

Loss on drying á731ñ— Dry it in vacuum at 105for 5hours:it loses not more than 1.0%of its weight.

Residue on ignition á281ñ: not more than 0.1%.

Limit of mercaptopurine— Prepare three solutions in 6Nammonium hydroxide containing,respectively,20mg of Azathioprine per mL,20mg of USP Azathioprine RSper mL,and 200µg of USP Mercaptopurine RS,on the anhydrous basis,per mL.Apply 5-µLvolumes of the solutions at points about 2cm from the bottom edge of a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of microcrystalline cellulose.Allow the spots to dry,and develop the chromatogram in a suitable chamber,using butyl alcohol,previously saturated with 6Nammonium hydroxide,as the solvent,until the solvent front has moved about 15cm from the point of application.Remove the plate,air-dry,and locate the spots by viewing under short-and long-wavelength UVlight:any spot in the chromatogram from Azathioprine,other than the principal spot,is not more intense than the spot in the chromatogram obtained with USP Mercaptopurine RS(1.0%).

Organic volatile impurities,Method IVá467ñ: meets the requirements.

Assay— Dissolve about 300mg of Azathioprine,accurately weighed,in 80mLof dimethylformamide.Add 5drops of a 1in 100solution of thymol blue in dimethylformamide,and titrate with 0.1Ntetrabutylammonium hydroxide VS,using a magnetic stirrer,and taking precautions to prevent absorption of atmospheric carbon dioxide.Perform a blank determination,and make any necessary correction.Each mLof 0.1Ntetrabutylammonium hydroxide is equivalent to 27.73mg of C9H7N7O2S.

Expert Committee:(PA6)Pharmaceutical Analysis 6

USP28–NF23Page 206

Phone Number:1-301-816-8389