Amperometric determination of serum lactate dehydrogenase activity using an ADP-modified graphite electrode Original Research Article

Graphite electrodes modified with a drop-coated layer of polyethyleneimine (PEI) and adenosine diphosphate (ADP) displayed an electrocatalytic response to NADH after the adenine moiety of ADP was electrochemically oxidised. NADH can be detected amperometrically in alkaline solution (pH 9.0) at low applied potentials (+50 mV (Ag/AgCl)). Using a stationary electrode arrangement, linear response for NADH concentrations between 1.0×10−8 and 1.0×10−4 M was found, with a response time of 12 s and a detection limit of 8×10−9 M. The electrode was applied to the amperometric monitoring of the reaction between lactate and NAD+ catalysed by lactate dehydrogenase (LDH). A flow injection-amperometric method for the determination of LDH activity in human serum was developed. The method allows a fast and accurate discrimination between pathological and normal LDH activity levels, with a sampling rate of 40 h−1. Quantitative results for a random set of human serum samples were found to be in good agreement with the standard spectrophotometric method.