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 μm 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.