Simultaneous Determination of L- and D-Lactate by Enzyme Modified Carbon Paste Electrodes

Abstract
Enzyme modified carbon paste electrodes were developed for the determination of L- and D-lactate based on D-lactate dehydrogenase and L-lactate oxidase, respectively. D-lactate dehydrogenase was coimmobilized with a redox mediator bound to a polymer backbone and the cofactor NAD+. L-lactate oxidase and horseradish peroxidase were coadsorbed onto heat treated graphite powder, which was mixed with silicon oil to prepare the corresponding carbon paste. The electrodes were mounted in wall-jet flow cells, which were inserted in a split flow set-up. Both L- and D-lactate can be detected in the potential range from - 50 to 50 mV vs Ag/AgCl. L- and D-lactate can be determined simultaneously under flow injection (FI) conditions. Up to 40 samples can be analyzed per hour. The FIA set-up was automated. L-lactate has been determined in the range between 10 μM and 10 mM. The D-lactate determination range was 100 μM - 20 mM.

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