Sensitive Analysis of Chiral Phenoxy Acid Herbicides Using Anion-Selective Exhaustive Injection-Sweeping Micellar Electrokinetic Chromatography

Chiral pesticides, comprising enantiomers with identical physical and chemical properties but different biological effects, call for extra efforts in comprehensively evaluating their risk assessment. However, the defect regarding sensitive analysis of chiral pesticides limits the progress of research. Therefore, an efficient and highly sensitive analytical method for the trace-level analysis of chiral pesticides is imperative. Herein, normal micellar electrokinetic chromatography (MEKC), sweeping-MEKC, and anion-selective exhaustive injection-sweeping-MEKC (ASEI-sweeping-MEKC) were optimized to separate and enrich three chiral phenoxy acid herbicides (cloprop, dichlorprop, and fenoprop). Normal MEKC with 30 mM γ-cyclodextrin, 50 mM SDS, pH 2.5, and 50 mM phosphate buffer background electrolyte (BGE) achieved ideal chiral separation of target herbicides. Then, sweeping-MEKC was modified to enhance the detection sensitivity by 4690 to 10,630-folds with the conditions of pH 2.5, 100 mM phosphate buffer high-conductivity buffer (HCB), 60 s injection time + 30 mM γ-CD, 50 mM SDS, pH 2.5, 50 mM phosphate buffer BGE + 120 s sample injection time. ASEI-sweeping-MEKC achieved further improvement of detection sensitivity by 241,000- to 673,000-fold. And the optimal ASEI-sweeping-MEKC conditions for the target chiral phenoxy acid herbicides were 20% ACN water plug, 30 s injection time + pH 2.5, 100 mM phosphate buffer HCB, 60 s injection time + 30 mM γ-CD, 50 mM SDS, pH 2.5, 50 mM phosphate buffer BGE + 12 min sample injection time. All in all, these findings have validated ASEI-sweeping-MEKC as an efficient and powerful analytical method for the trace-level analysis of the enantiomers of three chiral phenoxy acid herbicides. This approach enables a comprehensive risk assessment and provides guidance for the sustainable application of chiral pesticides.