Pushing The Limits Of Targeted Pesticide Residue Quantitation: Part 1
Robust, reproducible quantitation of pesticide residues in food is the most important step in ensuring food safety, and hence, forms one of the most important responsibilities of every food safety laboratories. The analytical process involves characterization and identification followed by quantitation of pesticides across different food matrices. Considering the growing list of pesticides and their adverse effects even for very low concentrations, quantitation with confidence for every sample can pose some significant challenges to the analytical scientist.
Typical practices of using pesticides to control pests and improve yields can often pose a serious risk to human health if and when used inappropriately. Improper use of pesticides in breach of approved procedures, or those that are applied to crops for which their use has not been authorized, unacceptable amounts of these potentially dangerous compounds can find their way onto the plates of consumers.
In order to ensure food is safe for consumption, laboratories require robust, reliable and cost-effective workflows, incorporating highly effective sample preparation steps, separation methods and detection techniques. Owing to its selectivity, specificity, sensitivity, robustness and universal approach, liquid chromatography coupled to triple quadrupole mass spectrometers (LC-MS/MS) are widely used for quantitation of pesticides in food.
Food standards are growing increasingly stringent, so leading laboratories must ensure they consistently meet the requirements of regulators. Thankfully, the latest comprehensive pesticide workflow solutions are helping laboratories deliver the very highest quality of pesticide quantitation, on time and on budget.
Optimizing Sample Preparation
Regardless of the food product that is being tested, pesticide residue workflows typically start with sample preparation, following homogenization and residue extraction steps. This stage is one of the most important parts of the workflow, however, very often they are not highlighted.
The heterogeneity of the sample matrix, as well as the wide variety of pesticide compounds that must be extracted, can significantly add to the complexity of this task. For example, pesticide residues can be lost during sample grinding, compromising the accuracy of quantitative analysis. Loss of critical pesticides can also occur through hydrolysis by water or enzymatic degradation as enzymes are released from cells, or by the formation of insoluble complexes due to interaction of the analyte with matrix components. Each of these factors can impact the quantitation of pesticide residues in food.
Homogenization is followed by solvent extraction and cleanup. Extraction could traditionally be a time-consuming process, often requiring relatively large amounts of sample, and involving use of multiple solvents and work-up steps. In addition, results from this step can vary based on matrix type and pesticides that are being monitored. Time-consuming sample cleanup steps, based on separation techniques such as gel permeation chromatography, could also be necessary, thereby adding another layer of complexity.
The widespread adoption of sample preparation strategies based on QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) methods has significantly simplified the process of residue extraction for a wide range of food types, especially for high-moisture content samples. These generic extraction approaches, coupled with “quick and easy” cleanup techniques such as dispersive solid phase extraction, are able to comprehensively extract residues with a range of different chemical properties, resulting in more consistent and reliable quantitation.
The universal and easy-to-implement nature of QuEChERS methods has also allowed laboratories to reduce the complexity of their workflows. Their simplicity is such that many suppliers are now offering all-in-one kits containing all of the necessary pre-weighted reagents and supplies, which laboratories can use straight from the box. And as they require very little sample material, solvent or equipment, and eliminate the need for time-intensive homogenization steps, they are also helping to reduce laboratory waste and cut operational costs.
The Need for LC-MS/MS Technology
Once analytes are extracted from the matrix, food safety laboratories require reliable, sensitive and precise separation, detection and quantitation technologies to determine their concentration.
As indicated above, LC-MS/MS technology with triple quadrupole mass spectrometers are often the go-to choice for quantitation applications. The high selectivity and sensitivity of these instruments allow analysts to confidently identify pesticides against target lists and accurately quantify even trace levels. Figure 1 shows the distinct separation obtained for a leek sample spiked with more than 250 pesticides at a concentration of 100 µg/kg. The mass range, robustness, specificity, selectivity of the triple quadrupole instrument ensures the ability to handle a wide variety of sample types and deliver reliable results in a cost-effective manner.
Conclusion
To ensure the food on our plates does not contain potentially harmful levels of pesticides, laboratories require robust workflows for their analysis and targeted quantitation. Improvements in the sample preparation methods that are used to extract pesticide residues from food samples, as well as in the sensitivity, accuracy, robustness and reliability of the triple quadrupole instruments used for analyte detection, are helping food safety laboratories confidently quantify these compounds even in trace amounts.
Acknowledgements
This article is based on research by Katerina Bousova, Michal Godula, Claudia Martins, Charles Yang, Ed Georg, Neloni Wijeratne & Richard J. Fussell, Thermo Fisher Scientific, Dreieich, Germany, Thermo Fisher Scientific, California, USA, Thermo Fisher Scientific, Hemel Hempstead, UK.
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