A bienzyme modified carbon paste electrode for the amperometric detection of l-lactate at low potentials

Lactate oxidase (LOD) from Pedicoccus sp. and horseradish peroxidase (HRP) were coimmobilized on graphite powder, which was mixed with silicone oil to form a carbon paste electrode (CPE). HRP adsorbed or covalently bound on the surface of graphite particles enables highly sensitive detection of H2O2, generated by the LOD catalyzed oxidation of l-lactate, at potentials around 0 mV vs. Ag/AgCl. Interferences by direct electrochemical oxidation of easily oxidizable substances, e.g., uric acid, paracetamol and NaN3 can be prevented. The electrocatalytical interferences by substrates for peroxidase are discussed. To improve the sensitivity and the stability of the lactate sensor the influence of different immobilization procedures and the addition of polyethylenimine (PEI) were investigated. The ratio of the taken amounts of LOD to HRP was optimized. L-Lactate can be detected in the range between 3 μM and 10 mM (R.S.D. = 1–2.5% in the range between 0.1 and 5 mM) under flow injection conditions. The use of a wall-jet flow cell enables up to 90 injections (50 μl) per hour to be performed at a flow rate of 0.6 ml min−1. L-Lactate can be selectively determined in the presence of α-hydroxy- and α-ketocarboxylic acids.