Enantioseparation of pesticides by gas chromatography. Measurement of association constants enantiomer-chiral selector.

ABSTRACT

In this study, the association constants of sixteen pesticides with the chiral selector octakis(6-O-tert-butyldimethylsilyl-2,3-di-O-acetyl)-γ-cyclodextrin were determined. The procedure only involved a few experimental measurements; namely, gas hold-up time and retention time of pesticides in capillary columns, as well as column phase ratio at each temperature condition. Fundamental equations of gas-liquid chromatography were used to estimate association constants. Two sets of columns containing different concentrations of the mentioned chiral selector dissolved in (14 %-cyanopropyl-phenyl)-86 %-methyl-polysiloxane were used. One set included capillary columns without any chemical treatment and the other group included columns that were crosslinked. The systematic comparison between both groups indicated a deleterious effect of the crosslinking on enantioselectivity. Our main objective is to promote the use of gas chromatography for the analysis of volatile and semi-volatile chiral pesticides. Thus, we proposed a simple methodology, based only on chromatographic measurements, to obtain information about the enantiorecognition ability of a particular chiral selector constituting the stationary phase and the influence of the selected polymer on the selectivity experimentally obtained.