Determination of isoniazid in tablets by second-derivative ultraviolet spectrophotometry of scraped-spot solutions from thin-layer chromatography

Isoniazid in solutions of tablets was separated by thin-layer chromatography (TLC). The portion of the precoated plate carrying the isoniazid spot was cut out and the coating was scraped off into water. The isoniazid was quantified in the solution, without separation of suspended adsorbent, by second-derivative spectrophotometry, which eliminated the background in the zero-order spectra. Relative standard deviations (n = 5) were <1%. Results obtained for commercial tablets were in good agreement with those given by a liquid-chromatographic method.