Sensitivity improvement by using contactless conductivity rather than indirect UV detection for the determination of enantiomeric purity of amines by CE

A capacitively coupled contactless conductivity detection (C4D) system for CE with a flexible detection cell was applied for the enantioseparation of small chiral underivatized amines using chiral crown ether or CD as chiral selector. Since these compounds are poorly UV-active, C4D was an alternative detection mode. The composition (ionic strength, pH, chiral selector) of the electrolyte was optimized in order to be suitable for C4D. (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was required as chiral selector to resolve the enantiomers of small polar amines. However, trimethyl-beta-CD was suitable to separate amines possessing hydrophobic carbon chains. The performance of C4D was compared with indirect UV detection in terms of sensitivity, repeatability and accuracy. The linearity range of C4D was very large (1.5-1600 mu g/mL) compared with the indirect UV linearity range (25-400 mu g/mL) and allowed the determination of the enantiomeric purity of isopinocampheylamine up to 0.25%. The CE-C4D method has been fully validated by applying a novel strategy using accuracy profiles. All relative biases of the developed method were included within the +/- 15% limits of acceptance. C4D is a good alternative to indirect UV detection for the enantioseparation of non-UV absorbing amines since the method development is fast and easy and, the sensitivity is improved by a factor of 100 compared with that of the indirect UV mode.