Determination of selenoamino acids by coupling of isotachophoresis/capillary zone electrophoresis on a PMMA microchip

The design, the fabrication, and the analytical performance of a PMMA microchip for isotachophoresis and capillary electrophoresis are described. The microchip offers the possibility of on-line coupling of an isotachophoretic preconcentration step prior to the capillary electrophoretic separation. Conductivity detection with thin film platinum electrodes is used for monitoring of the enrichment and of the separation on the microchip. With the preceding ITP step an enrichment factor of about 80 can be achieved. The seleno amino acids selenomethionine, selenoethionine, and selenocystine can be separated down to a concentration range of just a few micromoles/L. With suitable selection and combination of electrolytes the microchip can be used for a wide field of applications.