Galvanic decoupling of a postcolumn amperometric detector in capillary electrophoresis

Abstract

A postcolumn amperometric detector for capillary electrophoresis techniques with galvanic decoupling of the detection electrodes and the detection circuit from the power unit of the detector (via a laboratory constructed d.c.-d.c. converter) and from the recording devices (via an opto-coupling device) was developed. The high insulating resistance achieved in this way (ca. 10 11−10 12 Ω ) reduced leak currents from the electrophoretic equipment through the detector to the low pA level. It was also effective in eliminating problems due to changes in the potential at the column outlet as found when current detection devices were used. The decoupling protected the detector in situations when the column outlet was at a potential of 4–5 kV. The detector was tested by isotachophoretic experiments carried out in a hydrodynamically closed separation compartment. Dispersions of the analyte zones in the detector were reduced about tenfold in comparison with a previous design of the detector. Experiments with a urine sample, however, revealed that the resolving power of the detector is limited in the isotachophoretic separations of complex mixtures of electrochemically active constituents. The use of a copper electrode was tested in the separation of triethylenetetramine and impurities present in its technical-grade preparation. This detection approach was shown to provide a high sensitivity for this amine and for impurities forming strong complexes with Cu(II) cations.