Photo Credit: Brett Stevens/Getty Images
A team of scientists from the University of Muenster and the University of Siegen in Germany has demonstrated the use of low temperature plasma desorption/ionization orbitrap high-resolution mass spectrometry (LTP–Orbitrap–HR–MS) for the analysis of pesticide residues in fruit.1
Pesticides are routinely used to protect crops from disease and infestation, and there is strict legislation in force to ensure that the maximum residue levels (MRLs) are adhered to. Quantification of pesticides in crops is therefore routinely performed to ensure the safety of consumers. Liquid chromatography (LC) or gas chromatography (GC) coupled to MS is typically used for this. However, it is the time-consuming sample preparation step that limits the applicability of this as a fast screening method.
In this study, the team evaluated which steps could be eliminated to develop a faster LTP–Orbitrap–HR–MS method with respect to European Union (EU) legislation. The team focused primarily on those pesticides that have been reported to exceed legal MRLs in Germany (acetamiprid, cyprodinil, fenhexamid, and fludioxonil). After method optimization, samples were analyzed by LTP–Orbitrap–MS to identify pesticides in spiked and unspiked fruit QuEChERS extracts.
Several experiments were performed to evaluate and confirm the method: Firstly, calibration curves with standard solutions of each pesticide were determined. Potential matrix effects in grape and raspberry extracts were evaluated with matrix matched calibrations and spiked samples. Matrix-matched calibration was applied for quantification because it was found that the fruit matrix (still present during extract analysis) had a significant effect on analyte ion abundance.
For most pesticides, linear working ranges greater than four orders of magnitude were achieved. Limits of quantification (LOQ) ranged from 0.001 mg/kg to 0.07 mg/kg; significantly below the permitted MRL. Method precision was below 14% relative standard deviation (RSD). These results were directly compared to results obtained from an LC–ESI–HR–MS method and were found to be in good correlation. Finally, the validated LTP–Orbitrap–HR–MS method was tested with unspiked fruit samples bought from a local grocery store. Pesticide residues of cyprodinil and fludioxonil (0.003–0.03 mg/kg) were easily detected in the shop-bought grapes and raspberries.
The team concluded that LTP–Orbitrap–HR–MS is a fast screening method for pesticide residues in fruit, particularly for those pesticides studied in the experiment. It is also suitable for highlighting those pesticides that exceed MRLs and can verify sub-MRLs in fruit.
1. Carsten Engelhard et al., Anal. Methods 6, 5463–5471 (2014).