Direct chiral liquid chromatography determination of aryloxyphenoxypropionic herbicides in soil: deconvolution tools...

In this paper, the enantiomeric separation of two aryloxyphenoxypropionic esters (fluazifop-butyl and quizalofop-ethyl) and a safener herbicide (mefenpyr-diethyl), which is widely used for protecting crop plants, has been studied by direct liquid chromatography (LC) with UV detection on an α(1)-acid glycoprotein as chiral stationary phase. Optimization of separation conditions was done by factorial experimental design. Experimental factors and ranges selected were propanol (5-10%), phosphate buffer pH (6.5-7.0), and column temperature (15-25 °C). Responses were expressed in terms of enantioresolution (R(s)) and adjusted retention time of the second eluted enantiomer (t(r2)'). The chemometric method used to explore data was response surface analysis. Multiple response analyses were carried out to determine the combination of experimental factors which simultaneously optimize experimental responses. Under optimum conditions for enantioseparation of each herbicide, partially overlapped or fully resolved enantiomers were obtained. Deconvolution tools were employed as an integration method to fit chromatographic data and to achieve a more precise enantiomeric ratio (ER) and enantiomeric fraction (EF) values. Applicability of both direct chiral LC and peak deconvolution methods was evaluated in spiked soil samples at different R/S enantiomeric ratios. Acceptable and reproducible recoveries between 71% and 96% with precision in the range 1-6% were achieved for herbicide-spiked levels from 0.50 to 9.0 μg g(-1). In addition, parameters such as R(s), ER, and EF were calculated and compared with values obtained using the common valley drop integration method.