Influence of Organic Modifiers on the Separation of Carboxylic Acids Using Co‐EOF Capillary Electrophoresis

Abstract

In this paper, a number of different electroosmotic flow (EOF) modifiers, including both organic solvents and ion‐pairing reagents, were systematically evaluated for their effect on the separation selectivity of carboxylic acids using the co‐EOF mode. Although, all organic solvents modified the EOF to some extent, the best separation selectivity of the tested carboxylic acids was achieved using acetonitrile (15% v/v) as the organic solvent modifier. High concentrations of tetramethylammonium hydroxide (TMAOH) in the background electrolyte (BGE) also improved separation selectivity. This resulted from changes in mobility due to the formation of complexes between TMAOH and the carboxylic acids, and the EOF. Excellent separation selectivity of nine carboxylic acids (oxalic, formic, fumaric, malonic, tartaric, citric, succinic, maleic, and acetic) was obtained using 70 mM TMAOH in a 25 mM KH₂PO₄ BGE at pH 6.0. The calibration curves were linear in a concentration range of 0.4–1 mM with detection limits ranging from 4–25 µM. The utility of the proposed method was demonstrated by determining the concentration of carboxylic acids in plant exudates.

Keywords:

• EOF modifiers
• CZE
• Carboxylic acids
• Plant exudates

Acknowledgment

Katherina Kanitsar thanks the extension Centre of the Vienna University of Technology for financial support during her stay at CSIRO, Land and Water, Adelaide Laboratories, South Australia.