title: Continuous-flow/stopped-flow system for determination of ascorbic acid using an enzymatic rotating bioreactor.
abstract: The high sensitivity that can be attained using an enzymatic system and mediated by hydroquinone, has been verified by on-line 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 catalyses the oxidation of hydroquinone to p-benzoquinone, whose electrochemical reduction back to hydroquinone is detected on glassy carbon electrode (GCE) surface at -0.15V. Thus, when l-ascorbic acid is added to the solution, this acid is reduced chemically (p-benzoquinone to hydroquinone) and acts as mediator of HRP, decreasing the peak current obtained proportionally to the increase of its concentration. The recovery of l-ascorbic acid from four samples ranged from 99.09 to 101.10%. This method could be used to determine l-ascorbic acid concentration in the range 12nM-3.5muM (r = 0.998). The determination of l-ascorbic acid was possible with a limit of detection of 6nM in the processing of as many as 25 samplesh(-1). The method was successfully applied for the analysis of l-ascorbic acid in pharmaceutical formulations.
authors.affiliation: Department of Chemistry. National University of San Luis. Chacabuco y Pedernera. 5700 San Luis, Argentina.
authors.forename: Germán A
authors.initials: GA
authors.lastname: Messina
authors.forename: Angel A J
authors.initials: AA
authors.lastname: Torriero
authors.forename: Irma E De
authors.initials: IE
authors.lastname: Vito
authors.forename: Julio
authors.initials: J
authors.lastname: Raba