Targeted pesticide residue analysis is a well-established and essential part of modern food testing. Laboratories routinely determine pesticides present in food samples against a specific target list to ensure food products comply with the maximum residue levels (MRLs) set by governments (European Commission) and national food safety authorities.
Explore this issueAugust/September 2017
Growing concerns over food safety and expanding international trade have led to the development and enforcement of stricter pesticide regulations in recent years. In 2014, China’s Ministry of Agriculture and Ministry of Health jointly issued a revised national food safety standard, which expanded the number of categories of pesticide residues and total number of MRLs. Together with the Japanese Positive List System and European Union (EU) Directive No 752/2014, these standards are amongst the strictest food safety regulations in the world.
Traditionally, separation technologies such as gas chromatography (GC) and liquid chromatography (LC), coupled with triple quadrupole (QqQ) mass spectrometry (MS), have formed the mainstay of targeted pesticide residue quantitation workflows. The high sensitivity and selectivity offered by these QqQ-based techniques allow analysts to confidently identify and quantify even trace levels of known contaminants, while their robustness ensures fast, reliable, and cost-effective routine analysis.
Yet new pesticides are continually being developed and applied to crops around the world. The growing complexity of global food supply chains means that pesticides approved for use in one country can unexpectedly end up in food consumed in another, where the pesticides are not approved. Other chemicals, previously undetected in food samples and not on target lists, can also enter food chains during product preparation, transport, and storage from an often-surprising range of sources.
As a result, food safety laboratories are not only faced with an increasing number of analytes to screen for—they must be vigilant for new chemicals too. Of course, all of this must be achieved with high turnaround times and at a competitive cost per sample. And as food safety standards continue to evolve, laboratories need to be sure that the technology they use today will still meet their needs five years down the line.
Confident Routine Quantitation
Food safety is an evolving field. Technological advances result in ever lower limits of detection and quantitation, and greater insight into the toxicological effects of the chemicals we use in industry and agriculture mean that MRLs are continually being revised. In 2016 for example, the EU announced amendments to regulations governing MRLs for a number of pesticides found in a wide range of products, including the organophosphate insecticide chlorpyrifos.
As food safety standards become increasingly strict, what was once the lower end of a permissible pesticide residue level may be the upper end tomorrow. Laboratories therefore need to be confident that the technology they depend on to quantify these analytes is ready for future challenges.
For instance, high-resolution accurate mass (HRAM) Orbitrap MS from Thermo Fisher Scientific offers sensitivity that can help to safeguard laboratories against changes in MRLs. Hybrid quadrupole Orbitrap mass analyzer instruments combine quadrupole precursor selection with high-resolution accurate mass detection of product ions. The data is acquired at a resolution that can surpass quadrupole-time-of-flight instruments. This selectivity and mass accuracy helps to lower or even eliminate interference and permit lower limits of detection and accurate quantification.
Since MRLs vary for different pesticide-commodity combinations, the techniques used to analyze pesticide residues must be able to identify and quantify analytes over a wide dynamic range. EU limits for pesticide residues in beetroot, for example, vary from 30 milligram/kilogram to as little as 0.03 milligram/kilogram depending on the analyte. The Thermo Scientific Q Exactive Focus hybrid quadrupole-Orbitrap mass spectrometer is an option to meet this challenge, enabling quantitation over a wide dynamic range.
Identifying the Unknown
Routine quantitation of analytes against target lists is incredibly important for the protection of consumer safety, yet for many food safety laboratories it’s only part of the story. As food supply chains become increasingly global and complex, the risk of contamination with previously undetected chemicals becomes greater. However, the detection and identification of these unexpected analytes can be one of the most challenging tasks in pesticide analysis.
While LC-QqQ tandem MS enables highly selective and sensitive quantitation and identification of hundreds of target pesticides in a single run, this approach requires extensive compound-dependent parameter optimization and cannot be easily adapted to screen for untargeted pesticides.
Full scan approaches, on the other hand, are able to screen for a much broader range of analytes, meaning the search is not limited to a pre-defined list of chemical suspects. With the right analytical tools, unexpected analytes can be identified and quantified at the same time as performing routine targeted and quantitative analyses.
However, as full scan approaches produce significantly more data than conventional approaches, it is essential to use data analysis software that can rapidly process results and cross reference against spectral libraries and compound databases in order to make sense of all this information. These software can quickly and automatically search online compound databases such as ChemSpider and mzCloud, or a laboratory’s own database of analytes, to determine empirical formulae or tentatively identify unknown compounds.
Boosting Laboratory Efficiency
With ever increasing numbers of residues to identify, food testing laboratories require robust, reliable, and efficient technologies that enable high productivity. And with budgets a key priority for many lab managers, these analyses must also be performed at a very low cost per sample.
One of the benefits of multi-residue screening based on HRAM Orbitrap MS is the ability to analyze multiple components simultaneously. Combining multiple pesticide workflows in a single run can help laboratories work more efficiently, increasing throughput and boosting productivity. Full scan approaches also allow laboratories to combine pesticide workflows with other types of analyte workflows, such as toxins and veterinary drugs. This way, laboratories can expand the analytical reach of their food testing workflows while minimizing the time and resources spent preparing samples for separate analyses. Furthermore, as HRAM Orbitrap MS approaches also facilitate retrospective analysis, analytes that are not currently on target lists can be identified at a later date without having to store and re-analyze samples.
In addition to advanced hardware, innovative informatics can also streamline workflows and boost productivity. Many forward-looking laboratories are using integrated method development and data analysis solutions that allow operators to conveniently modify pre-configured methods depending on the matrix or analytes of interest. Used in conjunction with cloud-based spectral library and compound database searching, these integrated software solutions can help minimize the time taken between sample injection and the analyst reaching a conclusion.
Simplifying Residue Extraction
One of the most important stages in pesticide quantitation is residue extraction. While full scan analysis workflows are able to screen large numbers of analytes faster and more efficiently than conventional QqQ techniques, they can only do this if the residues they are analyzing are fully extracted from the food matrix in the first place—and if the analytes are chromatographed and ionized.
In recent years, the widespread adoption of extraction techniques such as QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) have simplified the preparation of high-moisture food samples and overcome many of the limitations of conventional approaches. Early approaches typically involved the use of multiple, time-consuming procedures, and produced results that were highly matrix dependent. The QuEChERS method, on the other hand, is based on a single acetonitrile extraction step, with an optional dispersive solid-phase extraction clean-up step. However, although the method is generic, simple to implement, and amenable to a wide range of food samples, the extracts often contain high concentrations of co-extractives.
The latest separation technology is simplifying sample preparation. The Thermo Scientific TurboFlow inline clean-up technique, for example, is a complementary sample preparation approach that eliminates up to two-thirds of the steps required by traditional methods, permitting the injection of complex matrices directly into the instrument. Analytes are separated from the matrix using specialized chromatography columns packed with large particles that retain residues while larger molecules, such as lipids and proteins, pass through. The residues of interest can then be transferred to an analytical column and subsequently analyzed.
As food supply chains become increasingly global and complex, and residue screening workflows require the screening of ever larger numbers of expected and unexpected analytes, food testing laboratories requires robust solutions that can meet not only today’s food safety standards—but tomorrow’s analytes too.
Bromirski is Q Exactive product marketing manager at Thermo Fisher Scientific. Reach him at email@example.com.