ON LINE CONCENTRATION OF NEUTRAL ANALYTES FOR MICELLAR ELECTROKINETICCHROMATOGRAPHY - 5 - FIELD ENHANCED SAMPLE INJECTION WITH REVERSE MIGRATING MICELLES

Elementary conditions for the on-line concentration of neutral analyte s by field-enhanced sample injection with reverse migrating micelles f or micellar electrokinetic chromatography is presented. Acidic phospha te buffers containing micelles of sodium dodecyl sulfate are utilized as both sample solvent and separation solution. After the capillary is conditioned with a separation solution, a water plug is hydrodynamica lly injected to achieve field enhancement at the injection end of the capillary during injection by application of voltage. A model is provi ded to give insight into the stacking scheme. Significant detector res ponse improvements are confirmed experimentally. Moreover, utility of the technique for the analysis of a real sample is tested using urine spiked with testosterone and progesterone.