AN AMPEROMETRIC LACTATE SENSOR-BASED ON A NAD(-ANALOG AND LACTATE-DEHYDROGENASE COIMMOBILIZED ON RETICULATED VITREOUS CARBON())

A NAD(+)-analog was coimmobilized with lactate dehydrogenase (LDH) on reticulated vitreous carbon (RVC) to give an amperometric lactate bios ensor. Both LDH and the NAD(+)-analog were bound covalently with carbo diimide to the surface of the porous RVC-material. The electrode was o perated in a FIA-arrangement in the presence or absence of a soluble m ediator, Meldola Blue. The stability was poor when the electrode was o perated at +400 mV (vs. Ag/AgCl) in the absence of mediator but improv ed most significantly in the presence of 5 mu M mediator, so that 65% of the original activity remained after 16 days. The amperometric curr ents were smaller with regeneration by mediator at -100mV than with di rect electrochemical oxidation at +400 mV, indicating that the additio nal steps slow down the reaction rate. Linear calibration plots were o btained from the detection limit, 1 mu M, to 500 lambda M lactate with 5 mu M mediator, reoxidized at -100mV. The sample throughput was abou t 60 h(-1).