Evaluation of Methylated Silica Solid-Phase Extraction Sorbent to Retain a Surfactant in the Detection of Pesticides in Water Using Ultra-Performance Liquid Chromatography–Tandem Mass Spectrometry

Abstract

This study examined the matrix effect of a typical surfactant on the detection of pesticides in water using ultra-performance liquid chromatography–electrospray ionization tandem mass spectrometry (UPLC–ESI–MS/MS). When direct sample injection is employed, surfactants in water samples tend to adsorb onto the chromatographic column, weakening its analyte separation capability and consequently lowering signal detection intensities and raising detection limits. A new sample preparation approach of a tailored solid-phase extraction (SPE) is proposed based on the difference in adsorption affinities between surfactant and pesticide for silylated surfaces. Using sodium dodecyl sulfate (SDS) as a representative surfactant, four types of silylated silica particles with different surface hydrophobicity and functionality were examined for selectively adsorbing and removing SDS from water samples with pesticide analytes to eliminate the matrix effect of the surfactant on liquid chromatographic (LC) separation. It was found that the tailored SPE sample preparation for cleanup of SDS could be effectively achieved based on this concept. Samples prepared with trimethylchlorosilane methylated silica particles in the tailored SPE produced a desirable LC separation and low detection limits for the pesticide analytes. The linear calibration range extended from 0.1 up to 40 μg L−1 (R 2 = 0.9906–0.9998, n = 6). Low limits of quantitation for the 11 pesticides were achieved (0.027–0.090 μg L−1). The precision of the proposed method for the 11 analytes was less than 10%.