Enantioseparation of polar pesticides on chiral capillary columns based on permethyl-β-cyclodextrin in matrices of different polarities

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

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.

Enantioseparation of agrochemicals by gas chromatography. Exploring columns based on cyclodextrin derivatives dissolved into polysiloxanes

The main goal of this work is to expand the availability of chiral columns for the analysis of agrochemicals by gas chromatography. A broader offer of chiral stationary phases would allow shifting toward enantioselective analytical techniques environmentally more friendly for those compounds. We prepared seven chiral capillary columns based on derivatives of either, β-cyclodextrin or γ-cyclodextrins dissolved at high concentrations, in two typical polysiloxanes with different polarities, demonstrating not only the significance of the chiral selector but also of the polymer solvent for achieving adequate enantioseparation of some agrochemicals. The enantiorecognition ability of each column was evaluated with 20 volatile and semivolatile agrochemicals, possessing one or two chiral centers. Besides, to elute more polar agrochemicals, as well as to enhance enantioselectivity, three derivatization procedures targeting the carboxyl and/or amine group were evaluated. The results revealed that the prepared column consisting of octakis(2,3-di-O-acetyl-6-O-tertbutyldimethylsilyl)-γ-cyclodextrin dissolved in (14%-cyanopropyl-phenyl)-86%-methyl-polysiloxane provides the broadest enantiorecognition capacity. This column allowed the enantioseparation of seventeen chiral agrochemicals, including metalaxyl, furalaxyl, and four imidazolinones, which were not enantioseparated in the remaining columns. To the best of our knowledge, glufosinate, fluorochloridone, fenarimol, furalaxyl, and four imidazolinones were enantioseparated by gas chromatography for the first time.

Ionic liquid stationary phase coating optimization for semi-packed microfabricated columns

This work highlights the effect of the stationary phase coating process on the separation efficiency of gas chromatography microcolumns. The stationary phase coating quality was characterized by three different bis(trifluoromethylsulfonyl)imide (NTf₂) anion based ionic liquids. The ionic liquids containing NTf₂ anion are used for gas chromatography due to their high temperature stability. In this work, the chemical and physical approaches of column deactivation as well as the temperature treatment were evaluated by separating a mixture of 20 organic components and saturated alkanes. The results show that higher oven temperature treatment provides higher efficiency while losing a bit of peak symmetry. The thermal treated 1-butylpyridinum bis(trifluoromethylsulfonyl) imide [BPY][NTf₂] stationary phase at 240°C demonstrated as high as 8300 plates per meter for naphthalene. This was a 5-fold increase in separation efficiency in comparison to those of the columns treated at 200°C. Albeit being within acceptable ranges, the peak tailing degraded from 1.17 to 1.46 for naphthalene when the processing temperature for coating increased. Both chemical and physical deactivation process increased separation efficiencies and peak resolution.