ONLINE COUPLING OF CAPILLARY ISOTACHOPHORESIS WITH CAPILLARY ZONE ELECTROPHORESIS

The on-line combination of capillary isotachophoresis (CITP) with capillary zone electrophoresis (CZE) in the column-coupling configuration of the separation unit was studied. The inherent concentrating power of the ITP stage was effective in achieving a high volume reduction of the injected sample so that the ZE separations with 2-3 μm plate heights could be achieved in 300 μm I.D. capillary tubes for nitrophenols and 2,4-dinitrophenyl-labelled amino acids taken as model analytes. Very reproducible migration times (0.3-1.2% relative standard deviations for 138-350-s migration times) and a high precision of sample injection (0.9-5.1% relative standard deviations for 8-pmol amounts of the analytes) could be typically achieved. Removal of the separated macroconstituents from the separation compartment after the ITP stage prevented column overloading in the ZE stage so that low detection limits could easily be achieved for the analytes (ca. 10-7 mol/L for a 5-μl injection volume by using a photometric detector) even in a 105-fold excess of a sample macroconstituent. © 1990.