Reusable 2-(Dimethylamino)ethyl Methacrylate Polymers On-line Solid-Phase Extraction Coupled to Liquid Chromatography Tandem Mass Spectrometry for Rapid Determination of Acidic Pesticides in Foods

Abstract

A rapid and easy method was developed for the sensitive determination of six acidic pesticides (2,4,5-trichlorophenoxyacetic acid, acifluorfen, methyl-4-chlorophenoxyacetic acid, fluroxypyr, haloxyfop, and bispyribac-sodium) in pear, apple, cucumber, and rice samples. This method was a full automatic platform using a novel polymeric monolith-based on-line solid-phase extraction (SPE) coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS). A poly(2-(dimethylamino)ethyl methacrylate-co-ethylene dimethacrylate) monolith was fabricated as the sorbent, and the morphology, surface area, and extraction performance of the polymers were characterized. With the addition of 10.0 mL of acetonitrile and 1.0 to 5.0 g of anhydrous NaCl, the food samples were homogenized and centrifuged. The extracted samples were directly loaded and cleaned on the polymers using a 5 mmol L⁻¹ ammonium acetate solution and subsequently eluted into the analytical column for next separation with an acetonitrile-1.5% formic acid solution as eluting solvent. The detection limit (S/N = 3) was 0.2 to 2.0 μg kg⁻¹ for the analytes, and the intra- and inter-day recoveries in pear, apple, cucumber, and rice samples ranged from 80 to 104%, and 83 to 115% with relative standard deviations of less than 13.5%. The developed on-line SPE LC-MS/MS protocol permits an automated and high-throughput determination in only 15 min. Moreover, the intra-batch (n = 5) and inter-batch precisions (n = 3) for the preparation of the polymers were lower than 11.6% and the sorbent was sufficiently stable for 500 extraction cycles without a significant loss in the extraction efficiency. The developed method was successfully applied to monitor six acidic pesticides in vegetable, fruit, and cereal samples.