An amperometric enzyme electrode for lactate based on graphite paste modified with tetracyanoquinodimethane

Abstract

An amperometric enzyme electrode for lactate is described. The construction of an enzyme electrode involves the incorporation of tetracyanoquinodimethane (TCNQ) and lactate dehydrogenase (LDH) into the graphite paste. The response of the electrode to lactate is based on the oxidation of NADH at 220 mV vs SCE based on a LDH catalyzed reaction through the mediated mechanism. Data are also reported on the oxidation of NADH within the TCNQ mediated graphite paste electrode without LDH as a function of binder composition. It has been found that the response of the electrode is decreased on increasing the binder ratio. This is attributed to the limited transport of NADH within the paste. Similarly, the effect of enzyme (LDH) concentration incorporated in the graphite paste vs the enzyme electrode response for NADH is also reported. An increase in enzyme concentration results in the decreased response of the electrode, again related to the limited mass-transport at the oil-solution interface. The response curve for lactate is slightly dependent on the anodic potential. The effects of interferences (pH and temperature) on the response of the enzyme sensor are also reported. It was found that the response is nearly constant within a 6·5-8·5 pH range whereas the variation of the temperature shows a biphasic curve on the response, probably attributed to the heterogeneous reaction at a lower temperature and homogeneous reaction at a higher temperature. The stability of the enzyme sensor is better, with a loss of a 45% response after 30 d on storage at room temperature in phosphate buffer (0.1 M, pH 7·5). © 1994.