Conductivity detection cell for capillary zone electrophoresis with a solution mediated contact of the separated constituents with the detection electrodes

A contact conductivity detection cell for capillary zone electrophoresis (C ZE) with an electrolyte solution mediated contact of the separated constitu ents with the detection electrodes (ESMC cell) was developed in this work. This new approach to the conductivity sensing in CZE is intended to elimina te detection disturbances due to electrode reactions and adsorption of the separated constituents when these are coming into direct contact with the d etection electrodes, An optimum detection performance of the cell was achie ved when the carrier electrolyte solution mediated the electric contact of the detection electrodes with the separated constituents. Different composi tions of the mediator and carrier electrolyte solutions led to large drifts of the detection signals. Isotachophoresis experiments performed in this c ontext with the ESMC cell revealed that origins of these drifts are in tran sport processes (diffusion and electromigration) between the detection comp artment and the detection electrodes in the cell. These processes affected, to some extent, other analytically relevant performance parameters of the ESMC cell of the present construction as welt [e.g., concentration limits o f detection (LODs), a contribution of the cell to the band broadening]. For example, the ESMC cell gave, under optimum operating conditions, 3-4 times higher concentration LODs for the test analytes than a current on-column c onductivity cell employed under identical working conditions. On the other hand, these LOD values (25-150 nmol/l) were still 20-5 times lower than tho se estimated from reference experiments for a contactless conductivity dete ctor. CZE experiments with iodide, carried out under working conditions lea ding to electrochemical reactions of this anion on the detection electrodes of current conductivity cells, did not occur in the ESMC cell. In addition , this cell, contrary to a reference contact conductivity cell, required no special carl (e.g., cleaning of the surfaces of the detection electrodes b y chemical or electrochemical means) to maintain its reliable long-term per formance. Anionic CZE analyses of tap and mineral water samples monitored b y the conductivity detector provided with the ESMC cell demonstrated a prac tical applicability and certain limitations of this detection approach in t he analysis of ionic constituents present in high ionic strength sample mat rices. (C) 2001 Elsevier Science B.V. AII rights reserved.