Fluorimetric determination of isoniazid by oxidation with cerium(IV) in a multicommutated flow system

A multicommutated flow system for the indirect fluorimetric determination of isoniazid was proposed. The analytical procedure was based on the oxidation of isoniazid by cerium(IV) and monitoring of the fluorescence intensity of the formed cerium(III). A time-based sample insertion enabled an effective control of the sampled volume and thus of the dispersion level attained. Highly concentrated samples were subject to a zone sampling approach, consisting on the removal to waste of selected sample portions, which acted as a selective dilution procedure enabling the expansion of the linear working range of concentrations without need for manifold re-configuration. These features were evaluated in automated dissolution studies. Linear calibration plots up to 1.37 mu-g ml(-1), with a relative standard deviation of less than 1.6% (n=12) and a sample throughput of about 50 samples per hour, were obtained. The lower detection limit was 34.3 ng ml(-1). The methodology was evaluated in the determination of isoniazid in pharmaceutical preparations and the effect of potential interferences was investigated. (C) 2000 Elsevier Science B.V. All rights reserved.