[Colorimetric determination of isoniazid in aqueous solutions and biological fluids]

Method has been developed for determination of tuberculostatic isoniazid in aqueous solutions and biological fluids. The principle of the method is that hydrazine group of isoniazid reacts with 1-fluoro-2,4-dinitrobenzene forming a red chromophor in alkaline medium. The absorbency maximum of the chromophor is at 530 nm. Biological fluids were deproteinized and diluted with acetonitrile then adjusted to pH = 8.2 with trometamol-hydrochloric acid buffer and reacted with 1-fluoro-2,4-dinitrobenzene dissolved in acetonitrile. The chromphore was measured colorimetricaly against a blank solution which did not contain isoniazid. The method was calibrated in the range of 1-30 mg/l isoniazid and reproducibility was checked with recovery % determinations.