Modified QuEChERS for Organophosphorus Pesticide Analysis in Agricultural Soils by Gas Chromatography-Tandem Mass Spectrometry

Summary

This protocol describes a modified Quick-Easy-Cheap-Effective-Rugged-Safe (QuEChERS) method with a magnesium silicate adsorbent-based dispersive solid-phase extraction cleanup for multiresidue determination of organophosphorus pesticides in agricultural soils by gas chromatography-tandem mass spectrometry, improving co-extractive removal, minimizing matrix-related analytical interference, and supporting reliable trace-level quantification.

Abstract

Accurate determination of organophosphorus pesticide (OPP) residues in agricultural soils by gas chromatography-tandem mass spectrometry (GC-MS/MS) is often hindered by matrix-induced signal effects caused by co-extracted organic matter, humic substances, and mineral-associated interferents. Conventional Quick-Easy-Cheap-Effective-Rugged-Safe (QuEChERS) cleanup strategies may not sufficiently remove matrix components from complex soil extracts, compromising analytical performance. This study presents a modified QuEChERS protocol that incorporates the adsorbent into mixed-sorbent dispersive solid-phase extraction (dSPE) cleanup for the simultaneous determination of 12 OPPs in agricultural soils by GC-MS/MS. Seven dSPE sorbent combinations were evaluated across six agricultural soils with varying soil properties. Co-extractive removal was quantified gravimetrically, and the combination of primary-secondary amine, octadecylsilane, and a magnesium silicate adsorbent (50 mg each, with 150 mg anhydrous magnesium sulfate) achieved the highest average co-extractive removal (88%). Analyte protectants consisting of ethylglycerol, L-gulonic acid γ-lactone, D-sorbitol, and shikimic acid were incorporated into final extracts to minimize matrix effects, while matrix-matched calibration compensated for soil-specific signal variation. Chlorpyrifos-methyl-d10 and triphenyl phosphate were employed as procedural and injection internal standards, respectively. Matrix-matched calibration curves (5–600 µg/kg) demonstrated excellent linearity, with coefficients of determination ≥0.9933 for most analyte-soil combinations. The limit of detection (5 µg/kg) was used for linearity assessment, whereas the method limit of quantification was established at 50 µg/kg as the lowest validated level. Accuracy and precision assessed at three recovery levels (50, 200, and 400 µg/kg, n = 5 per level) demonstrated recoveries between 70% and 120% with relative standard deviations ≤20% for most analyte-soil combinations, meeting SANTE/2020/12830 (Rev.2) performance criteria. Lower recoveries were observed only for fenamiphos, pirimiphos-ethyl, and ethion in selected soil matrices. The results demonstrate that the magnesium silicate adsorbent improves dSPE cleanup by reducing co-extractives and that its combination with analyte protectants and matrix-matched calibration provides reliable multiresidue determination of OPPs in complex soil matrices by GC-MS/MS.

Introduction

Organophosphorus pesticides (OPPs) remain among the most widely used classes of agrochemicals worldwide because of the broad-spectrum efficacy and versatility of this pesticide class in crop protection¹. Although many OPPs undergo environmental degradation more rapidly than organochlorine pesticides, widespread and recurrent application of these compounds results in continued presence in agricultural soils². Soil acts as the primary environmental compartment receiving pesticide inputs and can serve as a temporary reservoir from which residues may be transferred to crops, surface waters, groundwater, and surrounding ecosy....

Protocol

The source data underlying the experimental optimization of the dSPE cleanup procedure, the matrix effect dataset, and the physicochemical characterization of the six agricultural soils have been deposited in Zenodo and are publicly available at DOI: 10.5281/zenodo.21644870. The details of the reagents and the equipment used are listed in the Table of Materials.

1. Soil sampling and preparation

NOTE: To ensure personal safety, wearing a lab coat, protective eyewear, and nitrile gloves is recommended throughout this protocol.

1. Collect a bulk composite soil sample from t....

Results

The six agricultural soils selected for method evaluation represented a broad range of soil properties (see Table 2), including pH (soil:H₂O, 1:2) values ranging from 4.67 to 7.31, organic matter contents from 0.18% to 6.46%, and clay fractions from 22.9% to 48.5%. Five soils originated from agricultural regions of Colombia and one from Spain. This diversity was intentionally incorporated to evaluate the robustness of the proposed cleanup procedure across contrasting soil matrices, given that .......

Discussion

The determination of pesticide residues in soils remains analytically challenging due to the high variability in soil physicochemical properties and the resulting differences in co-extractive composition^{4,5,6,14,17,18,19,20,21}

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3-Ethoxy-1,2-propanediol (ethylglycerol)	Sigma Aldrich	260428-1G
Acetic acid	Sigma Aldrich	695092
Acetonitrile	Merck	1006652500
AOAC 20i/s autosampler	Shimadzu	221-723115-58
Balance	OHAUS	PA224
C18	Sigma Aldrich	52600-U
Centrifuge tubes, 2 mL	Eppendorf	4610-1815
Centrifuge tubes, 50 mL	Nest	602002
Centrifuge Z206A	MERMLE	6019500118
Column SH-Rxi-5sil MS, 30 m x 0.25 mm, 0.25 µm	Shimadzu	221-75954-30
Container, with cap, amber glass, 1000 mL	Sigma Aldrich	Z674176
Desiccator	Simax	415262302
Dispensette 5-50 mL	BRAND	4600361
D-Sorbitol	Sigma Aldrich	240850-5G
Ethyl acetate	Merk	1313181212
Florisil <200 mesh, fine powder	Sigma Aldrich	288705-50G
Formic acid	Merck	1002641000
GCMS-TQ8040	Shimadzu	211552
Injection syringe	Shimadzu	LC2213461800
L-Gulonic acid γ-lactone	Sigma Aldrich	310301-5G
Linner splitless	Shimadzu	221-4887-02
Magnesium sulfate (anhydrous)	Sigma Aldrich	M7506-2KG
Methanol	Panreac	131091.12.12
Milli-Q ultrapure (type 1) water	Millipore	F4H4783518
Pipette tips 10 - 100 µL	Biologix	200010
Pipette tips 100 - 1000 µL	Brand	541287
Pipette tips 20 - 200 µL	Brand	732028
Pipettes Pasteur	NORMAX	5426023
Pippette Transferpette S variabel 10 - 100 µL	BRAND	704774
Pippette Transferpette S variabel 100 - 1000 µL	BRAND	704780
Pippette Transferpette S variabel 20 - 200 µL	SCILOGEX	712111099999
Primary-secondary amine (PSA)	Sigma Aldrich	52738-U
Refrigerator/freezer	Haceb	NEV ALC 404
Shikimic acid	Sigma Aldrich	S5375-1G
Sodium acetate	Sigma Aldrich	241245-1KG
Software GCMSsolution	Shimadzu	223-18472-92
Stainless steel 2 mm mesh	Pinzuar	PS33N10
Test tube, glass, 10 mL	Sigma Aldrich	BR114508
Toluene	Merck	1083252500
Triphenyl phosphate (I-IS)	Sigma Aldrich	241288-50G
Vials with fused-in insert, 0.3 mL	Sigma Aldrich	29398-U
Vials, screw top, amber glass, 15 mL	Sigma Aldrich	27088-U
Volumetric flask, 10 mL	Sigma Aldrich	DWK28017-10
Vortex	Scilogex	82120004
Pesticides
Chlorpyrifos	Sigma Aldrich	45395-100MG	2921-88-2
Chlorpyrifos-methyl	Sigma Aldrich	45396-250MG	5598-13-0
Chlorpyrifos-methyl-d10 (P-IS)	Sigma Aldrich	90047-5MG	285138-81-0
Ethion	Sigma Aldrich	45477-250MG	563-12-2
Fenamiphos	Sigma Aldrich	45483-250MG	22224-92-6
Fenitrothion	Sigma Aldrich	45487-250MG	122-14-5
Fenthion	Sigma Aldrich	36552-250MG	55-38-9
Malathion	Sigma Aldrich	36143-100MG	121-75-5
Methidathion	Sigma Aldrich	36158-100MG	950-37-8
Parathion-methyl	Sigma Aldrich	36187-100MG	298-00-0
Pirimiphos-ethyl	Sigma Aldrich	45628-250MG	23505-41-1
Pirimiphos-methyl	Sigma Aldrich	32058-250MG	29232-93-7
Tolclofos-methyl	Sigma Aldrich	31209-250MG	5701804-9