Chiral separation of aryloxyphenoxy-propionate herbicides in a permethyl-β-cyclodextrin based column. Influence of temperature and mobile phase composition on enantioselectivity

LUBOMIRSKY, ESTER; PADRO JUAN MANUEL; DI LORETO, HÉCTOR; CASTELLS, CECILIA B.

Praga

Simposio; 45th International Symposium on High Performance Liquid Phase Separations and Related Techniques, Prague, Czech Republic; 2017

The aryloxyphenoxy-propionate herbicides (FOPs) control graminaceous weeds in broad-leaved crops such as soybean or sugar beet and constitute a kind of selective post-emergence herbicides [1]. All (FOPs) are, chiral and according to previous research, the R-isomers of (FOPs) are biologically more active than the S-isomers. The S-isomers fail to prevent agricultural crop pests and also show toxicity and side effects [2].The effect of temperature and mobile phase composition are important for understanding chromatographic behaviors of analytes in a given the stationary phase. This is especially true for enantiomeric separation. These operating variables affects retention, selectivity, system pressure, and column stability. Moreover, by varying column temperature, thermodynamic tests may be used to understand mechanisms of chiral recognition.In this work, a permethyl-β-cyclodextrin chiral stationary phase was used under reversed-phase conditions for the chiral separation of four aryloxyphenoxy-propionate herbicides (fenoxaprop-p-ethyl, quizalofop-p-ethyl and tefuryl and haloxyfop-p-methyl). The mobile phases were mixtures of methanol, ethanol, iso-propanol, n-propanol, tert-butyl alcohol or acetonitrile and water. The influence of mobile phase composition and column temperature (from 0 to 50 ºC) on the separation was investigated.The retention factors (k) and selectivity factor (α) for the enantiomers of all investigated herbicides decreased with increasing the temperature. The ln α vs. 1/T and ln k vs. 1/T plots for enantiomers of chiral herbicides were linear at the range of 0?50 ºC, except for ln k vs. 1/T plots when the mobile phase compositions were acetonitrile/water. The calculated thermodynamic parameters based on linear van?t Hoff plots showed that the chiral separation was controlled by enthalpy. Temperature and mobile phase have an important effect on the chromatographic results. However, influence of temperature and mobile phase composition on enantioseparation of solutes and conformation of chiral stationary phase are seldom considered simultaneously.References[1] A.H. Cobb, J.P.H. Reade, Herbicides and Plant Physiology, 2nd Ed., Wiley-Blackwell, Chichester, UK, 2010.[2] J.A.M. Holtum, R.E. Häusler, M.D. Devine, S.B. Powles, The recovery of transmembrane potentials in plants resistant to aryloxyphenoxypropanoate herbicides: A phenomenon awaiting explanation, Weed Sci. 42 (1994) 293?301.Acknowledgements Financial support from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (PIP-0244), Agencia Nacional de Promoción Científica y Técnica (ANPCYT 2014-3597 and 2015-2764) and Universidad Nacional de La Plata is acknowledged. J. P. is a researcher from CIC-PBA, E.L. and J. P. acknowledges their fellowships from CONICET.