Potentiometric detection for capillary electrophoresis: Determination of organic acids

A potentiometric detector was developed for CE and applied to the determination of aliphatic carboxylic acids (up to C-10). The electrodes used were of the ''coated wire'' type. Insulated Cu wires (from 100 to 250 mu m diameter), with only the tip of the wire exposed, were directly coated with ''liquid membrane'' phases. A quaternary ammonium salt and a lipophilic macrocyclic pentaamine were used as carrier molecules. The electrodes were positioned at the end of the capillary (''wall-jet'' type of construction). The best compromise between separation and detection characteristics was obtained with a HEPES buffer system. Detection limits of 100 fmol were obtained (injection by electromigration). Calibration curves were linear in the range of 0-25 pmol injected. The behavior of the detection system is discussed theoretically.