Proposed primary reference methods for the determination of some commercially important chiral aryloxypropionate herbicides in both free acid and ester forms

Liquid chromatographic enantiomer resolution ofN-hydrazide derivatives of 2-aryloxypropionic acids on a crown ether derived chiral stationary phase

The liquid chromatographic separation of the enantiomers of several N-hydrazide derivatives of 2-aryloxypropionic acids was performed on a crown ether type chiral stationary phase derived from (18-crown-6)-2,3,11,12-tetracarboxylic acid. The behavior of chromatographic parameters by the change of mobile phases and additives for the resolution of these analytes was investigated. The enantiomers of all analytes were base-line resolved with a mobile phase of 100% methanol containing 20 mM H2SO4. These results are the first reported for enantiomer resolution of chiral acids of 2-aryloxypropionic acids as their N-hydrazide derivatives.

Mechanism of chiral recognition in the enantioseparation of 2-aryloxypropionic acids on new brush-type chiral stationary phases

New brush-type chiral stationary phases (CSP I-IV) comprising N-3,5,6-trichloro-2,4-dicyanophenyl-L-alpha-amino acids (1-4) were prepared by binding of chiral selectors 1-4 to gamma-aminopropyl silica gel. To check the role of excess free aminopropyl groups, CSP V was prepared by binding N-3,5,6-trichloro-2,4-dicyanophenyl-L-alanyl-(3-triethoxysilyl)propylamide to unmodified silica gel. The best separation of racemic 2-aryloxypropionic acids (TR-1-13) was obtained with CSP I; the -(-)-S enantiomer were regularly eluted first, as determined by a CD detector. The mechanism of chiral recognition implies a synergistic interaction of carboxylic acid analyte with the chiral selector and achiral free gamma-aminopropyl units on silica. In fact, CSP V, which is lacking an achiral aminopropyl spacer, shows a lower separation ability for 2-aryloxypropionic acids, but a similar enantioselective discrimination of esters TR-19-20, in comparison with CSP I. CSP I-IV retain unaltered separation ability after a few months of continuous work using a large number of various mobile phases.

Enantiomeric separation of an aryloxyphenoxypropanoic acid by CE and LC

A capillary electrophoresis (CE) and an high performance liquid chromatography (HPLC) chiral separation have been developed for an aryloxyphenoxypropanoic acid, 2-[4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid, a new antitumor agent. The racemic mixture is analyzed, without derivatization, as the free acids. The CE assay is based on inclusion complexation with hydroxypropyl-beta-cyclodextrin. HPLC separation is achieved with a CSP column with the glycopeptide, teicoplanin, as the chiral selector. Both methods give baseline resolution to the R-and S-isomers. The methods were validated for assay and for optical purity assessment of the R-isomer. For assay, the HPLC method is precise (RSD < 0.6%), accurate (error, 0.5%) and linear (r2 = 0.9998). It is able to precisely (RSD = 0.5%) and accurately (error, 0.9%) detect 0.3-6.0% of one isomer (S) in the other (R). The CE assay is much less precise and accurate than HPLC. It is a good alternative to separate and detect the enantiomers, however.

Stereoselective analysis of acid herbicides in natural waters by capillary electrophoresis

A capillary electrophoretic method for the stereoselective analysis of aryloxypropionic and aryloxyphenoxypropionic acidic herbicides in ground water and river water was performed. Vancomycin and gamma-cyclodextrin were added to the background electrolyte (BGE) as chiral selectors. Water sample preconcentration was accomplished by solid-phase extraction on styrene-divinylbenzene packed cartridges (2 L of ground water and 1 L of river water). The analytical method allowed for the resolution of mecoprop, fenoprop, fluazifop and haloxyfop racemic mixtures in natural water samples spiked with enantiomer concentration levels in the range 0.1-0.13 ppb for ground water and 0.4-0.54 ppb for river water.

Enantioselective and nonenantioselective degradation of organic pollutants in the marine ecosystem

Enantiomeric ratios of 11 chiral environmental pollutants determined in different compartments of the marine ecosystem by chiral capillary gas chromatography and chiral high-performance liquid chromatography allow discrimination between the following processes: enantioselective decomposition of both enantiomers with different velocities by marine microorganisms (alpha-HCH, beta-PCCH, gamma-PCCH); enantioselective decomposition of one enantiomer only by marine microorganisms (DCPP); enantioselective decomposition by enzymatic processes in marine biota (alpha-HCH, beta-PCCH, trans-chlordane, cis-chlordane, octachlordane MC4, octachlordane MC5, octachlordane MC7, oxychlordane, heptachlor epoxide); enantioselective active transport through the "blood-brain barrier" (alpha-HCH); nonenantioselective photochemical degradation (alpha-HCH, beta-PCCH).