Indirect fluorescence determination of lactate and pyruvate in single erythrocytes by capillary electrophoresis

A scheme of using fluorescein as the fluorophore for indirect detection of anions was demonstrated. This system is quite stable at a fluorescein concentration of 100 microM even without any other buffer components. Different injection modes affect the limit of detection (LOD). A LOD of about 20 amol was obtained for lactate under optimal conditions. Lactate and pyruvate in the intracellular fluid of erythrocytes were measured in this manner. The average amounts in a single erythrocyte for lactate and pyruvate are 1.3 and 2.1 fmol, respectively, or a ratio of 1.6 for pyruvate to lactate. Variations of the absolute amounts and the ratios are fairly large among a group of 27 cells examined. This is consistent with the difference of cells in size and composition. Although the migration times changed by up to 20% during a series of runs from the influence of concomitants in the cells, the migration time ratio was maintained around 1.072 with 3% relative standard deviation.