Tag Archives: mass spectrometers

Debadeep Bhattacharyya, Thermo Fisher Scientific
In the Food Lab

Pushing The Limits Of Targeted Pesticide Residue Quantitation: Part 2

By Debadeep Bhattacharyya, Ph.D.
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Debadeep Bhattacharyya, Thermo Fisher Scientific

Detection and quantitation of pesticide residues in food is extremely important in food safety. Given the challenge of evaluating multiple pesticides at low levels across various samples, laboratories are in constant need of robust, reliable and sensitive analytical methods.

The risk of unauthorized pesticide overuse can increase residue concentrations in food, thereby, causing severe health issues. Global food safety bodies strictly regulate the levels of pesticides allowed in food products. In the European Union for instance, legislation in the form of Directive No 752/2014 sets statutory maximum residue limits (MRLs) for more than 1000 pesticides in food products of plant or animal origin.1 The number of pesticides and their allowed concentrations are necessary to ensure consumer safety, and are amongst the strictest in the world, permitting concentrations in products at levels typically as low as several parts-per-billion (ppb).

The requirements to achieve such low limits of quantitation for all analytes in a complex matrix present a significant analytical challenge for the food safety laboratories tasked with making a confident assessment of every sample. With perishable products such as fresh fruits and vegetables under routine analysis, these results need to be achieved within very short turnaround times and at a low cost per sample to meet lab managers’ budgets.

Advances in LC-MS/MS Technology

Recent advances in triple quadrupole technology have offered an additional boost to the existing analytical capabilities of liquid chromatography tandem mass spectrometry (LC-MS/MS). The segmented quadrupoles, faster rod drivers and more powerful electron multipliers can enable analysts to achieve the desired levels of robustness, mass accuracy, precision and sensitivity required to meet this challenge.

Improvements in instrument detection capability are pushing the limits of quantitation even further. Figure 1 highlights the amplified sensitivity of a triple quadrupole spectrometer for the determination of two pesticides in a leek sample—a particularly complex matrix with a high moisture content. For both chlormequat and 2-methyl-4-chlorophenoxyacetic acid (MCPA), the spectrometer delivers enhanced performance, giving analysts the ability to quantify residues far beyond the current limits required for MRL determination.

mass spectrometers
Figure 1. Representative chromatograms of chlormequat (positive ionization mode) and 2-methyl-4-chlorophenoxyacetic acid (negative ionization mode), in leek extract monitored using the TSQ Quantis MS (blue trace) and the TSQ Endura triple quadrupole MS (red trace) mass spectrometers.

Robust, Reliable and Reproducible

With potentially hundreds of perishable samples to analyze each day, food testing laboratories not only require the ultimate sensitivity, but sensitivity should be supported by speed and robustness.

One way in which analysts are achieving higher analytical throughput is through the use of shorter instrument dwell times. Although short dwell times in the past enabled productivity of sample analysis (more samples at the same time), they often came at the expense of robustness and sensitivity of the results. With the latest advances in triple quadrupole technology, short dwell times no longer compromise analysis.

Very effective quantitation of pesticide residues can be achieved using timed selection reaction monitoring (SRM). With the timed SRM approach, data acquisition is performed within a short retention time window around each compound of interest. This approach reduces the number of transitions that are monitored in parallel within the retention time window, while ensuring consistent quantitation even at low concentrations (see Figure 2).

Pesticide Residue Quantitation
Figure 2. Comparison of azoxystrobin peak areas (1 μg/kg in leek) obtained on 10th injection and 410th injection. Peak areas are consistent even when a low dwell time of 2.5 ms is used. The 410th injection demonstrates an adequate number of data points across the peak.

Another important point to consider is workflow robustness. For busy laboratories with large workloads and tight turnaround times, time-consuming daily instrument recalibration and frequent maintenance simply isn’t a viable option.

Triple quadrupole instruments are renowned for their experimental reliability that is delivered for every fast-paced environment, and the latest instruments are pushing expectations even further. Figure 3 demonstrates the precise levels of measurement reproducibility that can be achieved using a triple quadrupole MS. Peak areas for the pesticide residue atrazine, added to a leek sample at a concentration of 10 μg/kg, remained well within the expected ±20% range over 400 injections. Even when the system was placed into standby mode for 12 hours and subsequently restarted, consistent measurements could be obtained without any additional maintenance.

Pesticide Residue Quantitation
Figure 3. Atrazine peak areas (10 μg/kg in leek) monitored over 400 injections. Red lines represent ±20% atrazine response. Yellow lines show the point at which the system was placed in standby mode for 12 h. No system maintenance was performed between injections.

Conclusion

Technical advances in instrumentation and improvements in procedures have generated more robust LC-MS/MS processes to definitively detect trace pesticide residues. With limits of quantitation growing increasingly stringent year on year, such advances in technology are not only helping laboratories meet the quantitation challenges of today, but also prepare for those of tomorrow.

References

1. Commission Regulation (EU) No 752/2014 of 24 June 2014 replacing Annex I to Regulation (EC) No 396/2005 of the European Parliament and of the Council, 2014.

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.

Debadeep Bhattacharyya, Thermo Fisher Scientific
In the Food Lab

Pushing The Limits Of Targeted Pesticide Residue Quantitation: Part 1

By Debadeep Bhattacharyya, Ph.D.
2 Comments
Debadeep Bhattacharyya, Thermo Fisher Scientific

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.

Pesticide Residue Quantitation
Figure 1. LC-MS/MS chromatogram of leek extract spiked with more than 250 pesticides at 100 μg/kg. Results were obtained using a UHPLC system coupled with a triple quadrupole MS.

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.