GALVANIC DECOUPLING OF A POSTCOLUMN AMPEROMETRIC DETECTOR IN CAPILLARY ELECTROPHORESIS

A postcolumn amperometric detector for capillary electrophoresis techn iques with galvanic decoupling of the detection electrodes and the det ection circuit from the power unit of the detector (via a laboratory c onstructed d.c.-d.c. converter) and from the recording devices (via an opto-coupling device) was developed. The high insulating resistance a chieved in this way (ca. 10(11)-10(12) Omega) reduced leak currents fr om the electrophoretic equipment through the detector to the low pA le vel. It was also effective in eliminating problems due to changes in t he potential at the column outlet as found when current detection devi ces were used. The decoupling protected the detector in situations whe n the column outlet was at a potential of 4-5 kV. The detector was tes ted 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 des ign of the detector. Experiments with a urine sample, however, reveale d that the resolving power of the detector is limited in the isotachop horetic separations of complex mixtures of electrochemically active co nstituents. 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 sens itivity for this amine and for impurities forming strong complexes wit h Cu(II) cations.