Solvent— Use dimethyl sulfoxide.

pH7.0phosphate buffer— Dissolve 4.54g of monobasic potassium phosphate in water to make 500mLof solution.Dissolve 4.73g of anhydrous dibasic sodium phosphate in water to make 500mLof solution.Mix 38.9mLof the monobasic potassium phosphate solution with 61.1mLof the dibasic sodium phosphate solution.Adjust,if necessary,by the dropwise addition of the dibasic sodium phosphate solution to a pHof 7.0.

Standard preparations— Dissolve a suitable quantity of USP Adenine RS,accurately weighed,in hot water,cool,and dilute quantitatively with water to obtain a solution having a known concentration of about 0.19mg per mL.Pipet 5-mLportions into three 100-mLvolumetric flasks,dilute with 0.10Nhydrochloric acid,0.010Nsodium hydroxide,and pH7.0phosphate buffer,respectively,to volume,and mix.

Test preparations— Proceed as directed for Standard preparations,using the specimen in place of the Reference Standard.

Procedure— Obtain the UVabsorption spectra of the Test preparationsand the Standard preparationsconcomitantly,in 1-cm cells,covering the range between 220nm and 320nm,using water as the blank.The respective absorptivities,calculated on the dried basis,at the wavelengths of maximum absorbance,for each pair of corresponding solutions do not differ by more than 2.0%.

0.1N Perchloric acid— Standardize 0.1Nperchloric acid VSas follows.Transfer about 300mg of potassium biphthalate,accurately weighed,to a 150-mLbeaker,and dissolve in 80mLof a mixture of 100mLof glacial acetic acid and 300mLof acetic anhydride,by stirring.Titrate with the perchloric acid solution,determining the endpoint potentiometrically.Each 20.42mg of potassium biphthalate is equivalent to 1mLof 0.1Nperchloric acid.

Procedure— Transfer about 200mg of Adenine,accurately weighed,to a 150-mLbeaker,and dissolve in 80mLof a mixture of 100mLof glacial acetic acid and 300mLof acetic anhydride,by stirring.Titrate with 0.1N Perchloric acid,determining the endpoint potentiometrically.Perform a blank determination,and make any necessary correction.Each mLof 0.1N Perchloric acidis equivalent to 13.514mg of C5H5N5.