On-line concentration of neutral analytes for micellar electrokinetic chromatography - IV. Field-enhanced sample injection

Fundamental conditions for the on-line concentration of neutral analytes by field-enhanced sample injection (FESI) for micellar electrokinetic chromatography (MEKC) is presented. Long water plugs are injected into the capillary to effect an enhanced field during electrokinetic injection of samples at negative polarity. Optimization of the injection procedure is performed by modifying the composition of the micellar sample matrix containing one anionic surfactant. Stacking is found to be dependent on analyte retention factors and the nature of the pseudostationary phase. More than 20- and 100-fold improvements in peak height and peak area were confirmed experimentally. The applicability of the technique was tested using spiked urine samples following a simple liquid-liquid extraction step. (C) 1998 Elsevier Science B.V.