Chiral separation of ten arylphenoxypropionate herbicides on four chiral columns by supercritical fluid chromatography

Abstract

Many chemical products used in the agrochemical industries contain chiral centers and consist of one or two pairs of enantiomers, which can have important consequences regarding bioactivity. The resolution of racemates on an analytical level for herbicides development is vital. Investigative chiral arylphenoxypropionates are widely used as herbicides. The chromatographic chiral resolution of ten racemic arylphenoxypropionate herbicides using supercritical fluid chromatography was studied on Sino-Chiral OJ, Chiralcel OD-H, Chiralpak IB, and Chiralpak AD-H columns. A comparison was made between the chiral herbicide separations on Sino-Chiral OJ column using a pure carbon dioxide (CO₂) mobile phase and a CO₂ mobile phase with an added 1% modifier (methanol, ethanol, 2-propanol). The retention factors for enantiomers of the substances decreased upon adding an organic modifier. The enantiomeric separation ability of four chiral selectors with respect to the compounds was examined under various experimental conditions. The results indicated that the Sino-Chiral OJ column showed the best chiral recognition, yielding six analytical herbicides in baseline separation. Only one analyte was completely separated by the bonded-Chiralpak IB column, which had a lower chiral recognition ability than the coated chiral stationary phase columns. Clodinafop-propargyl and haloxyfop-methyl did not produce any separation under the investigation conditions. In addition, the chiral recognition mechanisms between the chiral stationary phase and the analyte enantiomers were clarified.