Flow injection system with chemiluminometric detection for enzymatic determination of ascorbic acid

A simple, selective and rapid method for determination of ascorbic acid fro m fruit juices was developed by combining a flow injection analysis (FIA) s ystem with a chemiluminometric detector and a reactor with L-ascorbate oxid ase immobilized on controlled pore glass. It was found that some reducing a gents (eg ascorbic acid and mercaptoacetic acid) give chemiluminescence wit h luminol in the presence of hexacyanoferrate (III) in an alkaline solution . We used this new type of chemiluminescent reaction for the enzymatic dete rmination of ascorbic acid. The background substraction method was used in order to avoid interference during ascorbic acid determination. Accordingly , two chemiluminometric signals were registered for each determination, one signal corresponding to the sample that passed through the enzymatic react or that decomposed the ascorbic acid completely, and the second signal corr esponding to the sample that does not pass through the reactor. The differe nce between the two signals corresponds to ascorbic acid from the sample. T he linear range of the method was 10-1000 mu mol/L of ascorbic acid and the detection limit was 5 mu mol/L The throughput was four samples/h and RSD 3 .13% (n = 10). This method was applied for determination of ascorbic in fru it juices. The results were compared with those found by the reference meth od, based on titrimetric determination with 2,6-dichlorophenolindophenol, a nd the concordance was excellent. Copyright (C) 2000 John Wiley & Sons, Ltd .