Sensitive determination of D-lactic acid in biological samples by high-performance liquid chromatography

D-Lactate in biological samples was converted into the hydrazone of pyruvate in the presence of D-lactate dehydrogenase, an NADH-reoxidation system using diaphorase, DL-6,8-thioctamide and hydrazine. The hydrazone was converted into 2-methylquinoxanol by o-phenylenediamine in hydrochloric acid, and then the quinoxanol was determined by high-performance liquid chromatography with fluorescence detection. The calibration curve of D-lactate was linear up to at least 60 nmol/ml, and the determination limit was 600 fmol. Using this method, D-lactate was determined in biological samples.