L-LACTATE OXIDASE ELECTRODE BASED ON METHYLENE GREEN AND CARBON PASTE

An amperometric L-lactate electrode based on methylene green (MG) and carbon paste chemically modified with L-lactate oxidase is described. The electrode action is based on the effective reduction of oxidized L-lactate oxidase by reduced MG (apparent rate constant = 1.7 x 10(6) l mol-1 s-1) and rapid electrochemical mediator conversion. The enzyme electrode generates an anodic current at 0.05-0.6 V vs. SCE. The pH optimum of the electrode is 7.0. The apparent Michaelis constant depends on the amount Of L-lactate, and varies in the range 4.1-9.7 mM. The maximum electrode sensitivity is 50.4 muA l mmol-1 cm-2 and does not depend on the oxygen concentration in solution. The electrode is insensitive to glucose and ethanol. At 0.15 V the response to L-ascorbic acid (40 muM) is equivalent to 9.8% of the normal physiological L-lactate level in blood. The enzyme electrodes were used for L-lactate determination in goat whole blood. They remained stable on storage in the dry state for at least 2 months.