QuEChERS Method for Pesticide Residue Analysis

Quenchers are used to diminish fluorescence intensity, thereby improving the detection of specific pesticides. In pesticide analysis, the quenching mechanism involves dynamic or collisional quenching. Here, the quencher and the pesticide molecule collide, causing energy transfer and reducing fluorescence intensity as a result. They minimize background fluorescence and unwanted signals that may interfere with accurate pesticide detection. This is particularly important in fluorescence-based detection methods, where the presence of quenchers can help improve the signal-to-noise ratio and the overall accuracy of the analysis.

QuEChERS significantly improves laboratory efficiency and throughput. This procedure requires only small quantities of solvent and can generate recoveries of 70-120% with RSDs <5% for a wide range of compounds.

The Quenching Process in Two Steps

1. Extraction

• Solvent extraction techniques are designed to achieve maximum yield of analytes from the base matrix.
• Solvent selection is important to minimize co-extracting compounds.
• Analytes are extracted from the matrix with acetonitrile and salts/buffers.

2. Cleanup

• Sample cleanup is necessary to reduce interferences.
• Interferences can damage analytical instrumentation and complicate analyte identification and quantification.
• The use of PSA, C18, GCB (Graphitized Carbon Black) or Z-Sep sorbents allow removal of sugars, lipids, sterols, organic acids, proteins, carotenoids, chlorophyll and other pigments prior to a GC-MS/MS or LC-MS/MS analysis.

1. Homogenize sample
2. Transfer sample to 50mL tube
3. Add ACN and internal standard and shake for 1 min
4. Extraction: Add extraction salts and centrifuge (55227-U for EN15662:2008 and 55234-U for 2007.01 AOAC)
5. Cleanup: Transfer supernatant to cleanup tube
6. Shake and centrifuge
   a) LC-MS/MS Analysis: Dilute extract with mobile phase
   b) GC-MS analysis: Analyze directly or after solvent exchange

The specific choice of quencher and its concentration will depend on the analytical method and the pesticides being targeted for detection.

Methods for Pesticide Analysis

EN 15662 QuEChERS Method

This method is a sample preparation technique used for the analysis of pesticide residues in food samples, including fruits, vegetables, and other food products.

AOAC 2007.01 QuEChERS Method

This method is used for the determination of pesticide residues in foods. Specifically, it is a multi-residue method for the analysis of over 300 pesticides and environmental contaminants in various food commodities.

QuEChERS Selection Guide

Products for the Extraction Step

Description	Quantity	Cat. No.
Method EN15662 :2008 (12 mL centrifuge tubes)
Supel™ QuE Citrate (EN) Tube – 4 g MgSO4, 1 g NaCl, 0.5 g NaCitrate dibasic sesquihydrate, 1 g NaCitrate tribasic dihydrate	50	55227-U
Supel™ QuE Citrate/Sodium Bicarbonate (EN) Tube – 4 g MgSO4, 5 g NaBicarbonate, 1 g NaCl, 0.5 g NaCitrate dibasic	50	55237-U
Method AOAC 2007.01 (12 mL centrifuge tubes)
Supel™ QuE Acetate (AC) Tube – 6 g MgSO4, 1.5 g NaAcetate	50	55234-U
Non buffered extraction tubes (12 mL centrifuge tubes)
Supel™ QuE Non-Buffered Tube 1 – 4 g MgSO4, 1 g NaCl	50	55294-U
Supel™ QuE Non-Buffered Tube 2 – 6 g MgSO4, 1.5 g NaCl	50	55295-U

Products for Cleanup (QuEChERS) Step

Method – EN15662:2008

Matrices*		Product Description	Cat. No. 2 mL Tubes	Cat. No. 15 mL Tubes
Groups 1, 2 and 3	General fruits and vegetables lightly pigmented	150 mg Supelclean™ PSA, 900 mg MgSO4	—	55437-U
		25 mg Supelclean™ PSA, 150 mg MgSO4	55172-U	—
	Pigmented fruits and Vegetables Moderate levels of chlorophyll and carotenoids	150 mg Supelclean™ PSA, 15 mg Supelclean™ ENVI-Carb™, 900 mg MgSO4	—	55446-U
		25 mg Supelclean™ PSA, 2,5 mg Supelclean™ ENVI-Carb™, 150 mg MgSO4	55147-U	—
	Pigmented fruits and vegetables High levels of chlorophyll and carotenoids	150 mg Supelclean™ PSA, 45 mg Supelclean™ ENVI-Carb™, 900 mg MgSO4	—	55464-U
		25 mg Supelclean™ PSA, 7,5 mg Supelclean™ ENVI-Carb™, 150 mg MgSO4	55176-U	—
Groups 4, 5 and 6	Pigmented fruits and vegetables with waxes/lipids High Lipid Content	150 mg Supelclean™ PSA, 150 mg Discovery® DSC-18, 900 mg MgSO4	—	55439-U
		25 mg Supelclean™ PSA, 25 mg Discovery® DSC-18, 150 mg MgSO4	55173-U	—

Method – AOAC 2007.01

Matrices*		Product Description	Cat. No. 2 mL Tubes	Cat. No. 15 mL Tubes
Groups 1, 2 and 3	General fruits and vegetables lightly pigmented	400 mg Supelclean™ PSA, 1200 mg MgSO4	—	55466-U
		50 mg Supelclean™ PSA, 150 mg MgSO4	55287-U	—
	Pigmented fruits and Vegetables Moderate levels of chlorophyll and carotenoids	50 mg Supelclean™ PSA, 150 mg MgSO4, 50 mg ENVI-Carb™	on request	—
	Pigmented fruits and vegetables High levels of chlorophyll and carotenoids	50 mg Supelclean™ PSA, 150 mg MgSO4, 50 mg Discovery® DSC-18, 50 mg ENVI-Carb™	55289-U	—
		400 mg Supelclean™ PSA, 1200 mg MgSO4, 400 mg Discovery® DSC-18, 400 mg ENVI-Carb™	—	55474-U
Groups 4, 5 and 6	Pigmented fruits and vegetables with waxes/lipids High Lipid Content	50 mg Supelclean™ PSA, 150 mg MgSO4, 50 mg Discovery® DSC-18	55288-U	—
		400 mg Supelclean™ PSA, 1200 mg MgSO4, 400 mg Discovery® DSC-18	—	55470-U

Specialty Products for Method EN15662 or AOAC 2007.01 – Alternatives

Matrices*		Product Description	Cat. No. 2 mL Tubes	Cat. No. 15 mL Tubes
Groups 4, 5 and 6	Fatty or pigmented matrix With less than 15% fat	20 mg Z-Sep, 50 mg Discovery® DSC-C18 (alternative)	55284-U	—
		120 mg Z-Sep, 300 mg C18 (alternative)	—	55506-U
	Hydrophobic analytes in fatty matrices	75 mg Z-Sep (alternative)	55411-U	—
		50 mg Z-Sep, 150 mg MgSO4 (alternative)	55417-U	—
		500 mg Z-Sep (alternative)	—	55491-U
		300 mg Z-Sep, 900 mg MgSO4 (alternative)	—	55503-U
	Fatty matrices With greater than 15% fat	75 mg Z-Sep+ (alternative)	55408-U	—
		50 mg Z-Sep+, 150 mg MgSO4 (alternative)	55414-U	—
		500 mg Z-Sep (alternative)	—	55486-U
		300 mg Z-Sep+, 900 mg MgSO4 (alternative)	—	55511-U
	Improved recovery of planar pesticides in green matrices	Supel™ QuE Verde, 150 mg MgSO4, 10 mg ENVI™-Carb Y, 50 mg PSA, 60 mg Z-Sep+	55447-U	—
		Supel™ QuE Verde, 1200 mg MgSO4, 80 mg ENVI™-Carb Y, 400 mg PSA, 480 mg Z-Sep+	—	55442-U