Large-volume stacking in capillary electrophoresis using a methanol run buffer

Highly sensitive nonaqueous capillary electrophoresis of weakly acidic organic compounds has been performed using methanol as the run buffer solvent. Methanol provided appropriate suppression of the electroosmotic flow and an increase in the electrophoretic mobilities of anionic solutes compared to water. These two effects allowed large-volume stacking using the electroosmotic flow pump (LVSEP) to be achieved for larger anions using a bare fused-silica capillary under an electric field of reverse polarity, whereas only fast-moving small anions were previously known to be suitable for LVSEP in aqueous media. A field-enhanced sample injection of an additional amount of analytes during the solvent plug removal further enhanced the limits of detection to below the nanomolar range with conventional UV absorption detection. Under optimum conditions, excellent linear responses and reproducibility in the migration times together with the corrected peak areas for ten analytes were obtained in the concentration range of 10-100 nM.