Trace Enantioselective Determination of Imidazolinone Herbicides in Various Food Matrices Using a Modified QuEChERS Method and Ultra-Performance Liquid Chromatography/Tandem Mass Spectrometry

Abstract

A modified QuEChERS method was developed for simultaneous enantioselective determination of three imidazolinone herbicides (imazethapyr, imazamox, and imazapic) in two oil crops (soybeans and peanuts) and three food crops (wheat, maize, and rice) by chiral reversed-phase ultra-performance liquid chromatography/tandem mass spectrometry. Sample extraction was performed with 20 mL of methanol adjusted to pH 4 with 1% aqueous acetic acid. The supernatant was then cleaned with a primary secondary amine and graphitized carbon black. Several significant factors affecting the performance of the method were optimized. Under the optimum conditions, good linearity (R2 ≥ 0.9931) and acceptable recoveries (63.5–111.5%, relative standard deviation ≤ 22.7%) were obtained for each enantiomer. The limits of detection and quantification ranged from 0.34 to 1.5 μg/kg and 1.1 to 5.0 μg/kg, respectively. For all three imidazolinone herbicides, the S-enantiomers eluted before the R-enantiomers. Finally, several food samples (soybeans, peanuts, wheat, maize, or rice) were analyzed by this method. The enantiomers of the three imidazolinone pesticides (imazethapyr, imazamox, and imazapic) were not found in these samples at the microgram per kilogram level.