Enantioseparation of DL‐isocitric acid by a chiral ligand exchange CE with Ni(II)‐D‐quinic acid system

Abstract

The ratio of citric acid to D-isocitric acid can be used to distinguish authentic and adulterated fruit juices. To separate DL-isocitric acid enantiomers, we used ligand exchange CE. D-Quinic acid was used as a chiral selector ligand and Mn(II), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) ions were used as the central ions of the chiral selector in the BGE. DL-Isocitric acid was found to be enantioseparated with the above metal ions except for Mn(II) ion. The optimum running conditions for the analysis of D- and L-isocitric acids along with citric acid, an isomer of isocitric acid, were found to be a BGE (pH 5.0) containing 30% ACN, 20 mM acetic acid, 20 mM NiSO(4), and 80 mM D-quinic acid. Under these conditions, DL-isocitric and citric acids in fruit juices were analyzed successfully.

Mechanism of change in enantiomer migration order of enantioseparation of tartaric acid by ligand exchange capillary electrophoresis with Cu(II) and Ni(II)–D‐quinic acid systems

“…Previously, we reported enantioseparation of racemic tartaric acid by ligand exchange CE with Cu(II) and Ni(II) as the central ions and D-quinic acid as the chiral selector ligand [11,12]. Interestingly, while D-tartaric acid migrated…”

“…Accordingly, the m obs value is larger for the enantiomer of tartarate that forms the ternary complex more largely. In the previously reported CE conditions [12], it is probable that the 1:1 Cu(II)-D-quinate complex having the selectivity for D-tartarate was formed largely at the low D-quinic acid concentrations and the 1:2 Cu(II)-D-quinate complex with selectivity for L-tartarate was formed largely at the higher D-quinic acid concentrations. Therefore the EMO appeared to be reversed depending on the Cu(II)-D-quinic acid molar ratio [12].…”

“…On the other hand, in the Ni(II)-D-quinic acid system, racemic tartaric acid was not enantioseparated at the lower D-quinic acid molar ratios while L-tartaric acid preceded D-tartaric acid at the relatively higher molar ratios [12].…”

“…Since anionic tartarate and the 1:1:1 and 1:2:1 ternary Cu(II) and Ni(II) complexes migrate toward the negative pole against the charge attraction by EOF in the CE conditions previously reported [12], the observed electrophoretic mobility (m obs ) is expressed by Eq. (1) using the negative effective electrophoretic mobility (m eff ) and electroosmotic mobility (m eof ):…”

Mass spectrometry detection as an innovative and advantageous tool in ligand exchange capillary electrophoresis

“…This can be verified by the number of papers dealing with this technique and by the continuous developments observed. Besides the most frequent investigations using copper(II) ion, borate ion [8][9][10][11], and recently in several papers zinc(II) [12][13][14][15][16] and sometimes nickel(II) [17] were used as central ions. Furthermore, applications were developed in microchip CE (ME) [18], in the use of ionic liquids [19], for kinetic studies [16], and in the first, at our knowledge, non-chiral application of LECE [20], just to cite some of the most interesting developments.…”