Two-step stacking of cationic analytes by field enhanced sample injection and micelle to solvent stacking in capillary electrophoresis

Abstract

Capillary electrophoresis (CE) with ultraviolet (UV) detection suffers from a poor concentration sensitivity resulting in a significant obstacle for analysis of part per billion (ppb) levels. Therefore, in this study, a rapid and sensitive capillary zone electrophoresis (CZE) method with field enhanced sample injection and micelle to solvent stacking (FESI-MSS) was developed and validated for the determination of paraquat and bromhexine in river water without sample pre-treatment. The separation was carried out in an uncoated 40 cm × 50 µm fused-silica capillary with an applied voltage of 20 kV. The electrophoretic analysis was performed by 100 mM phosphate buffer with 20% acetonitrile at pH 2.5. Before sample injection, a micellar solution (10 mM sodium dodecyl sulphate; SDS in 80 mM phosphate buffer at pH 2.5) and an organic solvent rich solution (30% acetonitrile) was hydrodynamically introduced into the capillary. The detection wavelength was 195 nm for paraquat and 210 nm for bromhexine. From this study, the sensitivity of FESI-MSS technique compared with normal CZE was 1000-fold. Adaptability to real sample analysis was evaluated using spiked river water samples.