MEMBRANE-BASED ON-COLUMN MIXER FOR CAPILLARY ELECTROPHORESIS ELECTROCHEMISTRY/

One of the drawbacks of chemically modified electrodes for electrochem ical detection in conjunction with capillary electrophoresis (CE) is t hat the optimal ran buffer for the CE separation is often not compatib le with the electrolyte conditions necessary for maximum detector resp onse. This paper reports the development of a membrane-based on-column mixer for CE which makes it possible to perform the separation and de tection using different buffer conditions. The mixer consists of a cel lulose acetate tube ca. 2-mm length and 50-mm i.d. The pH and/or ionic strength of the CE run buffer can be altered at the detector end by p lacing the mixer in a cathodic buffer reservoir containing a modifying solution of either HCl or NaOH. Ions from the modifying solution diff use through the membrane into the detector end of the capillary and ca use the desired change in pH. The use of this system was demonstrated for the detection of several biologically important compounds by capil lary electrophoresis- eletrochemistry (CEEC) using chemically modified elec trodes. This included the use of a CoPC electrode for the detect ion of ribonucleosides, a D-amino acid oxidase electrode for the detec tion of amino acids, and a mixed-valent RuCN electrode for the detecti on of disulfides. Detection limits and detector stability were improve d over those reported previously for unoptimized systems.