Potentiometric detection of organic acids in liquid chromatography using polymeric liquid membrane electrodes incorporating macrocyclic hexaamines

Potentiometric detection employing coated-wire electrodes was applied to th e determination of organic acids in liquid chromatography (LC). Poly(vinyl chloride)-based liquid membranes, incorporating lipophilic macrocyclic hexa amines as neutral ionophores were used as electrode coatings. The selectivi ty and sensitivity of the macrocycle-based electrodes were found to be supe rior to an electrode based on a lipophilic anion exchanger (a quaternary am monium salt). Sensitive detection was obtained for the di- and tricarboxyli c acids tartaric, malonic, malic, citric, fumaric, succinic, pyruvic, 2-oxo glutaric and maleic acids after separation in reversed-phase LC. Detection Limits (signa1/4 sigma (noise)=3) of 6 pmol for malonic acid and 2 pmol for maleic acid were attained. The detection was explained using a molecular r ecognition model. The hexaamine-based potentiometric electrodes had a 1-s r esponse time at 1 mi min(-1) flow-rates. They were stable for at least 4 mo nths, with an intra-electrode variation of 3.2% (n=5). (C) 2001 Elsevier Sc ience B.V. All rights reserved.