SOLID-STATE FIELD DECOUPLER FOR OFF-COLUMN DETECTION IN CAPILLARY ELECTROPHORESIS

Palladium metal has been used to construct a robust and easy-to-handle field decoupler for capillary electrophoresis (CE) for use with off-c olumn detection. The tubular Pd electrode is applied as part of the wa ll of the capillary system. The capacity of the decoupler to pass the electrolytically generated hydrogen is high enough to accommodate the electric currents as usually found in CE. The use of the palladium dec oupler imposes some demands on the buffer to be used as the background electrolyte. Simple monovalent buffer ions are allowed. With multival ent buffer ions such as phosphates, pH shifts during the separation ar e observed in the separation capillary. The zone broadening in the dec oupler, equivalent to a dead volume of 15 nL, restricts the number of theoretical plates that can be obtained to approximately 100 000 with the capillary system used in this study. Further improvements in this respect are therefore necessary. It is shown that, with the decoupler as developed, electrochemical detection (ECD) is easily combined with CE. Detection limits for catecholic compounds with ECD were in the low fentomole range, 1 order of magnitude or more below those obtained wi th on-column UV detection.