Flow Systems with MnO2-coated Open Tubular Reactors for Spectrophotometric Determination of Ascorbic Acid in Pharmaceutical Products

A novel strategy for preparing polyethylene open tubular reactors coated with MnO2(s) was pioneered for flow analysis in order to minimize the inherent drawbacks of packed solid reagents. As an application, the determination of ascorbic acid in pharmaceuticals was selected. The method involved reduction of Mn(IV) by ascorbic acid, release of the formed Mn2+ ion, reaction with formaldoxime, and spectrophotometric monitoring. The influence of flow pattern was investigated by using two similar flow systems relying on constant or pulsed flow delivered by peristaltic or solenoid pumps. With pulsed flow, system versatility and ruggedness were improved, and the analytical sensitivity (0.01143Lmg(-1) ascorbic acid), detection limit (0.6mgL(-1) ascorbic acid), and sampling rate (60h(-1)) evaluated compared to constant flow were improved by 2.1%, 40.0%, and 6.5%, respectively. At the same time, the reagent consumption (2.8mg per determination) and analytical precision (relative standard deviation of approximately 2.5%) were maintained. One can conclude that the mixing conditions did not limit the analyte/reagent interaction. The results were in agreement with the British Pharmacopoeia method.