Abstract: The method for an on-line reaction of micro lactate dehydrogenase in capillary electrophoresis using electrophoretically mediated micro-assay(EMMA) coupled with electrochemical detection(EC) was developed. The running electrolyte(pH 9.2) was composed of 50 mmol/L Tris HCl, 10 mmol/Lnicotinamide adenine dinuceotide(NAD⁺), 5.0 mmol/Llithium lactate and 0.2 mmol/Lcetylpridinium bromide(CPB). LDHwas injected into the capillary. As it migrated electrophoretically in the capillary, LDH catalyzed the reaction between lactate and NAD⁺. The product NADH of the enzyme-catalyzed reaction was monitored by a bundle of carbon fiber electrode(150 μm diameter) held at +0.8 Vvs. SCE. The detection limits for LDHactivity using constant voltage mode and zero-voltage mode in EMMAwere determined to be 11×10^-9 Uand 60×10^-10 U, respectively. The formulae concerning the width or the height of the plateau in the electropherogram for EMMAwere deduced, and some significant conclusions were drawn from these formulae. The developed method has been used for the determination of ultramicro LDHactivity in serum with satisfactory results.

Key words: Capillary electrophoresis, Electrochemical detection, Lactate dehydrogenase