Two rapid, simpleand sensitive flow injection methods were developed for the estimation of metronidazole (MRZ) in pharmaceutical formulations. The proposed methods were based on charge transfer reaction between metol (N-methyl-p-aminophenol sulfate) as a π-acceptorand reduced MRZ as an n-donor to produce a blue colored chargetransfer complex. Method A depends on the reaction of reduced MRZ with metol (MT) in the presence of NaIO4 using two lines manifold to form blue colored product exhibiting absorption maxima at 700 nm.While method B depends on charge transfer reaction of reduced MRZ with MT in presence of a solid phase reactorcontainingfixedFePO4 on cellulose acetateusing reverse flow injection manifold to form a blue colored productwhich was measured spectrophotometrically at690 nm.Various experimental parameters for both methods were studied. Beer's law was obeyed in the ranges of2.5-200 and 2.5-150 μg mL-1,with r2 of 0.9995 and 0.9972;whilethe detection limit values were2.53 and 2.12μg mL-1 for methods A and B, respectively. Both of the suggested methods were successfully applied for the estimation of MRZ in commercial formulations. The results of the developed methods were compared with those obtained by the British pharmacopeia method, showinghigh accuracy and precision.
