Capillary batch injection – A new approach for sample introduction into short-length capillary electrophoresis with electrochemical detection

A novel concept for sample introduction into short-length capillary electrophoresis with electrochemical detection is presented. The capillary batch injection (CBI) principle is combined with capillary electrophoresis (CE) using a short piece of a fused silica capillary (7 cm in length with an inner diameter of 25 μm) to perform electrophoretic separations as fast as in chip electrophoresis. Small sample volumes are handled with the help of a capillary connected to a microprocessor-controlled microlitre syringe. This arrangement allows precise injections of nanolitre volumes onto the inlet of the separation capillary. The separation voltage of up to 2 kV is continuously applied to the separation system during sample injection and separation which results in favourable baseline characteristics of electrochemical detection (ED).The analytical performance of the CBI-CE–ED system was studied using noradrenaline, l-dopa and ascorbic acid as model analytes in tetraborate electrolyte solution. It was found that the adjustment of suitable convective conditions in the injection cell played the most important role for the analytical characteristics such as sensitivity, precision, and efficiency. For a suitable set of experimental parameters CBI-CE–ED offers fast and efficient separations complemented by reliable ED response characteristics.