Mass Spectrometry-Compatible Enantiomeric Separations of 100 Pesticides Using Core–Shell Chiral Stationary Phases and Evaluation of Iterative Curve Fitting Models for Overlapping Peaks

Abstract

Pesticides are often chiral, and their isomers have different activity, toxicity, metabolism, and degradation properties. Perhaps, the most complex are the synthetic pyrethroid insecticides that have up to 8 stereoisomers, but not all are active. Pyrethroids are toxic to aquatic invertebrates and non-targeted species like honey bees since they persist in the environment. Extensive biological studies of the pyrethroid enantiomers are limited. Possibly, this is because liquid chromatography enantiomeric methods for these studies often have limitations with mass spectrometry (MS) compatibility. In this study, an effective methodology was developed with MS compatible solvents to evaluate several core–shell (superficially porous particle, SPP) chiral stationary phases (CSPs) for the enantiomeric separation of several classes of chiral pesticides. The CSP with the broadest selectivity or spectrum amongst all pesticide classes was the hydroxypropyl-β-cyclodextrin. The other CSPs (cyclofructan, macrocyclic glycopeptide, and quinine-based selectors) had more selective applications including separations of the pesticides with amine or acid functionalities. Overall, 74 of 100 pesticides were baseline-separated. Most of the remaining ones had multiple stereogenic centers and had only one overlapping pair. Such cases were evaluated with a convenient peak area extraction protocol by iterative curve fitting. This approach will lead to more facile enantiomeric analyses where MS is needed to overcome complex matrices and reduce extensive method optimization.