[Stability of isoniazid and its related compounds. I. Separatory determination of isoniazid and its degradation products].

Abstract

Separatory determination of isoniazid (INAH) and its degradation products, isonicotinic acid (INA), isonicotinamide (INAA), and 1, 2-diisonicotinoylhydrazine (Bis) was established. (1) INAH is determined colorimetrically using sodium 1, 2-naphthoquinone 4-sulfonate. (2) Separation of INA is effected by passing the sample solution through a column of a weak cation-exchange resin (Amberlite CG-50 (H+ form)), by which INA alone is not absorbed, and INA in the effluent is determined colorimetrically using cyanogen bromide. (3) After sample solution is oxidized by ferricyanide in alkaline medium, the reaction mixture is passed through a column of a strong anion-exchange resin (Dowex 1×8 (Cl- form)), by which INAA is unchanged and not absorbed by the resin. The effluent is brought to pH 1 and INAA is determined by measurement of UV absorbance at 263mμ. (4) Bis is determined by measurement of absorbance at 329mμ of sample solution brought to pH 8.9 by adding 0.05M borate buffer solution and substracting the absorbance of INAH, which is calculated from concentration of INAH separately obtained by colorimetry with sodium 1, 2-naphthoquinone 4-sulfonate.