Continuous-flow/stopped-flow system for determination of ascorbic acid using an enzymatic rotating bioreactor

The high sensitivity that can be attained using an enzymic system and mediated by hydroquinone, has been verified by online interfacing of a rotating bioreactor and continuous flow/stopped-flow/continuous-flow processing. Horseradish peroxidase, HRP, [EC 1.11.1.7], immobilized on a rotating disk, in presence of hydrogen peroxide catalyzes the oxidn. of hydroquinone to p-benzoquinone, whose electrochem. redn. back to hydroquinone is detected on glassy carbon electrode (GCE) surface at -0.15 V. Thus, when L-ascorbic acid is added to the soln., this acid is reduced chem. (p-benzoquinone to hydroquinone) and acts as mediator of HRP, decreasing the peak current obtained proportionally to the increase of its concn. The recovery of l-ascorbic acid from four samples ranged from 99.09 to 101.10 . This method could be used to det. l-ascorbic acid concn. in the range 12 nM-3.5 micro M (r = 0.998). The detn. of l-ascorbic acid was possible with a limit of detection of 6 nM in the processing of as many as 25 samples h-1. The method was successfully applied for the anal. of l-ascorbic acid in pharmaceutical formulations. [on SciFinder (R)]