ON-COLUMN SAMPLE PRECONCENTRATION USING SAMPLE MATRIX SWITCHING AND FIELD AMPLIFICATION FOR INCREASED SENSITIVITY OF CAPILLARY ELECTROPHORETIC ANALYSIS OF PHYSIOLOGICAL SAMPLES

An on-line sample concentration method using sample matrix switching a nd held amplification peak stacking has been developed. A microbore LC guard column is used to slightly retain the analytes in order to swit ch from a high ionic strength sample matrix (the physiological fluid) to a low ionic strength matrix (the LC mobile phase). The eluted LC pe ak is then trapped in a CE system and preconcentrated by field amplifi cation peak stacking. The concentrated sample peak is then analyzed by CE. Compared to normal hydrodynamic injection, the sensitivity was in creased by more than 500-fold without loss in resolution. A limit of d etection of less than 10 nM for a physiological sample was achieved us ing UV adsorption detection. This method can be used for negatively or positively charged analytes.