Indirect Sequential Injection Enzymatic Determination of Allopurinol in Pharmaceuticals Based on Xanthine Oxidase Inhibition

Two automatic sequential injection analysis methodologies were developed for the enzymatic determination of allopurinol in pharmaceutical formulations. Both methodologies were based on the inhibition by allopurinol of the reaction catalysed by xanthine oxidase, assessed by spectrophotometric detection of the reaction product (uric acid) at 295nm. One methodology was established after a single readout at a fixed time while the other was based on the decrease of the rate of formation of uric acid upon monitoring the absorbance change. The analytical performance of both methodologies was validated, providing low environmental impact tools for assessment of allopurinol in drugs.