Nuclear magnetic resonance chiral discrimination of fipronil and malathion agrochemicals: A case study

The aim of the present study was to optimize a protocol for nuclear magnetic resonance (NMR) chiral discrimination to be used to determine the enantiomers ratio of agrochemicals. For this goal, the commercial agrochemicals fipronil and malathion were employed as active targets due the distinct physicochemical properties. We used the cyclodextrins to evaluate the chiral discrimination in aqueous media and chiral solvent agents to check in organic media. The fipronil chiral discrimination was accessed by β-CD in aqueous solution, although this procedure was ineffective for malathion due the low solubility. In organic media, the NMR chiral discrimination was successful for both agrochemicals and sensitive to dilution process. The NMR experiments explore very sensitive nuclei, for instance ¹ H, ¹⁹ F, and ³¹ P, in a simple, practical and low residue experimental protocol.

Some thoughts about enantioseparations in capillary electrophoresis

In this overview the goal of the authors was to analyze from the historical perspective the reasons of success and failure of chiral capillary electrophoresis. In addition, the current trends are analyzed, unique advantages of capillary electrophoresis are highlighted and some future directions are discussed.

Enantioseparation of nicotine alkaloids in cigarettes by CE using sulfated beta-CD as a chiral selector and a capillary coated with amino groups

Nicotine (NC) and its related compounds (cotinine (CN), nornicotine (NN), anatabine (AT) and anabasine (AB)) were simultaneously enantioseparated by CE using a capillary with amino groups and sulfated beta-CD as a chiral selector. The optimum running conditions were found to be 30 mM acetate buffer (pH 5.0) containing 8% sulfated beta-CD with an applied voltage of +15 kV at 30 degrees C using direct detection at 260 nm. Using a capillary coated with amino groups, the EOF migrates toward the positive pole. However, when sulfated beta-CD was added to the BGE, it was found that the EOF migrated toward the negative pole due to ionic adsorption of sulfated beta-CD to amino groups on the capillary inner wall. All the cationic analytes migrated as anions, suggesting that they formed stable anionic complexes with sulfated beta-CD. With this system and a simple pretreatment with mini-cartridges, NC alkaloids in five cigarette samples were enantioseparated. As a result, each of the compounds except for CN was detected. In the case of NC, only (S)-NC was detected (more than 99.9%), but in the case of NN, AT and AB, the ratios of (S)-isomer to total isomers were in the ranges 58-70, 81-85 and 59-65%, respectively. On the other hand, only NC was detected in cigarette smoke and the ratio of (S)- and (R)-NCs was 96:4. The amounts of NC alkaloids in cigarettes suggest that the production of (R)-NC resulted from racemization due to the high temperature/burning of the cigarette.

Pesticide analysis in tomatoes by solid-phase microextraction and micellar electrokinetic chromatography

The analysis of a group of seven pesticides (i.e. six fungicides: pyrimethanil, procymidone, nuarimol, fenarimol, benalaxyl and penconazole and one insecticide: pirimicarb) in tomato samples by micellar electrokinetic chromatography is investigated. For this purpose, reversed electrode polarity stacking mode and solid-phase microextraction (SPME) have been used as on-line and off-line preconcentration procedures, respectively. Tomato samples were first homogenized and extracted with acetone. After suitable evaporation and reconstitution of the extract in water, a SPME procedure using poly(dimethylsiloxane)/divinylbenzene fibers was used. Due to the strong influence of the sample matrix in the extraction, a matrix matched calibration of spiked tomato samples was developed. The method was found to be linear between 0.5 and 2.5 mg/kg. Limits of detection achieved are below the maximum residue limits established by the European Union and Spain legislation as well as by the Codex Alimentarius (except for penconazole). The potential of the method was demonstrated by analyzing 12 tomato samples (of ecological and non-ecological production) taken from regional cultivars. No residues of the selected pesticides were detected in any of the samples.

Enantioseparations by using capillary electrophoretic techniques. The story of 20 and a few more years

This paper provides the author's insight on the past, present and future of performing enantioseparations using capillary electrophoretic (CE) techniques. These techniques are discussed from the historical point of view, as well as based on their potential as the separation techniques of today and the future. The overview covers mechanistic as well as practical aspects of CE techniques.