GC-MS/MS Determination of Pesticide Residues in Fruit Using the Xevo TQ-GC

In this application note we describe a multiresidue GC-MS/MS method for the determination of pesticide residues in fruit commodities, with extraction using the QuEChERS workflow. The Xevo TQ-GC System provided excellent, fit-for-purpose performance in terms of linearity and calibration range for both organic raisin and apple. The trueness and precision of the GC-MS/MS method determined at three QC levels was found to be acceptable with the representative compounds shown, giving %RSD <10%.

Overall the performance data indicate that the Xevo TQ-GC, when used in combination with an established extraction protocol such as QuEChERS, is suitable for checking MRL/tolerance compliance in routine laboratory testing.

Benefits

Provides a multiresidue GC-MS/MS method for the determination of pesticide residues in fruit commodities, with extraction using the QuEChERS workflow, suitable for monitoring for MRL compliance. This method which was developed on Waters Xevo TQ-GC provides fit-for-purpose performance in terms of sensitivity, linearity, and robustness.

Pesticide residues remain a priority on the list of food safety concerns. As a result, laboratories are required to create analytical methods capable of screening the maximum amount of compounds, using a minimal number of methods, while ensuring sample turnaround times are met. The majority of countries have established clearly defined regulations¹ relating to pesticide residues, with legislation imposing Maximum Residue Limits (MRLs)² levels for different food commodities. To meet these criteria, laboratories require analytical techniques that are sensitive, accurate, and robust.

Multiresidue analysis is challenging due to the varying matrix complexity of different food commodities and the requirement for low part per billion (ppb or mg/kg) detection levels to achieve MRL compliance for a diverse range of pesticides. Currently there are in excess of 1000 pesticides known to be in use, and laboratories are continually under pressure to increase the scope of analytical methods employed for routine monitoring purposes. Various technologies are used to meet these challenges with the most common being liquid chromatography (LC) and gas chromatography (GC) coupled to tandem quadrupole mass spectrometry (MS/MS), which allows laboratories to cover a wide range of compounds as required by legislation.³

In this application note we provide example performance data from Waters Xevo TQ-GC System for pesticide residues in two different commodities. Samples were extracted by the QuEChERS CEN method and cleaned-up by dispersive solid phase extraction (d.SPE), following the protocol described in a EURL-FV multiresidue method, using QuEChERS for fruits and vegetables.⁴

Sample preparation and extraction

Homogenized organic apple was extracted using the QuEChERS method as shown in Figure 1. Organic raisin was first rehydrated with LCMS water and then the equivalent to 5 g of sample was taken for QuEChERS extraction. The supernatant from the QuEChERS extracts were then cleaned-up by d.SPE tubes which contained 25 mg of primary secondary amine (PSA) sorbent and 150 mg MgSO₄, per 1 mL of sample extract. Samples were then evaporated and reconstituted in ethyl acetate, post spiked with the pesticide mix, and analyzed using the gas chromatography, mass spectrometry method highlighted below. Analyte extraction recovery was not assessed during this work, QuEChERS is a well established sample extraction method for pesticides in food and the aim of this work was to assess the GC-MS/MS method performance only.

The performance of the GC-MS/MS step of the method was assessed using SANTE guidelines⁵ for 150 pesticides. Solutions of matrix-matched standards were prepared over the range 0.001 to 0.050 mg/kg (1.0 to 50.0 ppb in vial concentration) in apple, and 0.002 to 0.100 mg/kg (1.0 to 50.0 ppb in vial concentration) in raisin. Replicate injections at three concentration levels were run between bracketed calibration curves to assess the performance of the method. An internal standard (triphenylphosphate) was added to all samples prior to the analysis to correct for any injection variability which may have occurred.

Method development or method transfer on a new GC-MS/MS system can be time consuming, requiring parameters such as MRM transitions, collision energies, chromatography conditions, and processing methods to be optimized. To speed up this process, Quanpedia Database was used to automatically establish these parameters with minimal manual optimization required. An example of the Quanpedia workflow is shown in Figure 2.

The linearity of the method was assessed using bracketed matrix-matched calibration curves, which were internal standard corrected. Figure 3 shows the calibration curves for alpha-BHC in both organic apple and raisin.

The linearity of response and calibration range in organic raisin for all 150 pesticides assessed in this study are shown in Figure 4. The calibration curve data for all 150 compounds can be found in Appendix 1. The concentration levels take into account that only 5 grams of rehydrated raisin sample was taken for extraction. All compounds gave excellent linear response and only one compound, trans-nanochlor, gave a linear response <0.990. All residuals (back calculated concentrations) were within the 20% tolerance of the SANTE guidelines, with calibration ranges between either 0.002 mg/kg or 0.005 mg/kg to 0.100 mg/kg.

Replicate (n=6) injections were run for three levels, 0.005 mg/kg, 0.010 mg/kg, and 0.020 mg/kg in each matrix. The calculated mean concentrations and precision for representative pesticides in organic raisin are shown in Figures 5 and 6.

Ion ratios and retention times from the matrix-matched standards agreed well with the reference values and most were within the required tolerances (±30 % and ±0.1 min, respectively). An example of the ion ratios given by each of the QC levels for deltamethrin in organic raisin and apple can be seen in Figure 7.

The goal of this study was to evaluate the performance of the Xevo TQ-GC for the determination of pesticide residues in fruit commodities prepared by QuEChERS sample preparation methodology. The Xevo TQ-GC provided excellent, fit-for-purpose performance in terms of linearity and calibration range for both organic raisin and apple. The trueness and precision of the GC-MS/MS method determined at three QC levels was found to be acceptable with the representative compounds shown, giving %RSD <10%. Overall the performance data indicate that the Xevo TQ-GC, when used in combination with an established extraction protocol such as QuEChERS, is suitable for checking MRL/tolerance compliance in routine laboratory testing.

1. European Union (2009) Regulation (EC) No 1107/2009 of the European Parliament and of the Council of 21 October 2009 Concerning the Placing of Plant Protection Products on the Market and Repealing Council Directives 79/117/EEC and 91/414/EEC.
2. European Commission (2016) EU Pesticide Database.
3. K Organtini, G Cleland, E McCall, S Hird. (2017) UPLC and APGC Multiresidue Pesticide Analysis on a Single Tandem Quadrupole Mass Spectrometer Platform. Waters application note no. 720006013en.
4. European Union Reference Laboratory – Fruits and Vegetables, ‘Multiresidue Method Using QuEChERS Followed by GC-QqQ/MS/MS and LC-QqQ/MS/ MS for Fruits and Vegetables’.
5. European Union (2017). Document No. SANTE 11813/2017. Guidance Document on Analytical Quality Control and Method Validation Procedures for Pesticides Residues Analysis in Food and Feed.