Mass Spectrometry Pesticides Detection in Modern Food Safety and Testing

Food safety and testing has become an increasingly important industry, covering a wide range of areas — from import screening to domestic profiling and many areas in between

The food testing industry aims to:

• Ensure adherence to consumer safety and regulatory compliance.
• Fortify consumer reliance on food labeling and authenticity.
• Remove food-borne illness, adulteration, and other threats of contamination.
• Instill confidence in nutritional, dietary, and other health-related content.

Here we take a look at state-of-the-art mass spec methods and technologies which are carving an ever-deepening impact in the world of modern food safety and testing.

What are pesticides?

Pesticides and herbicides are used in modern agricultural practices for the control of pests which may effect crop yiled. The potential for excess levels and persistence through the food production cycle presents a constant threat to consumers.

According to the United Nations Food and Agriculture Organization, a pesticide is any substance or mixture of substances intended for preventing, destroying, or controlling any pest. This definition includes pests in and on: crops, livestock, feedstock, or any of the materials used for cultivation, harvesting, processing, preserving, transporting, and storage of consumer foodstuffs. This widely inclusive definition points out the potential for pesticides contamination from any of a multitude of entry points in the food production chain.

Although used in various forms for many years, strict regulations for pesticides use and testing largely arose in the latter half of the last century in the wake of concerns over human and environmental health. Today there are strict guidelines for the production and use of each pesticide type and application. Those that are allowable must be scientifically tested to ensure the active substance is both effective and safe without harmful effects on growers, consumers, animals, and the environment.

What are the challenges of pesticides testing?

A key metric for an approved pesticide (or plant permissible product (PPP)) is the establishment of the maximum residue level (MRL). These tolerances are the levels not to be exceeded when pesticides are used according to label instructions. These limits are also the sensitivity benchmark which testing instruments must achieve in order to be effective in a given testing application.

Sensitivity is not the only testing hurdle. A successful testing platform must detect an extensive panel of compounds within a wide array of sample matrices. Labs can be tasked with analysis of up to 1600 substances at low levels in a variety of food samples, from fruits and cereals to animal products and dietary supplements. Furthermore, the potential exists, particularly in the import/export trade, where standards for allowable use and MRLs may not apply or be adequately followed across the global markets.

What are the types of agricultural samples used for testing?

Consumer pesticides testing involves a wide range of agricultural products, each with unique requirements and challenges. As examples:

• Fruits and vegetables testing can involve a range of well-characterized pesticides detected with high sensitivity. The range and complexity of sugars, lipids, waxes, and other matrix components, however, can vary widely and thereby complicate sample analysis.
• Grains and cereals can involve matrices that vary according to plant type and sampling methods. Samples may be devoid of sufficient water and require effective solubilization strategies for analysis.
• Cannabis, similar to leafy greens in general, can be challenged by the presence of chlorophyll, cellulose, waxes, as well as variations in plant sampling techniques or requirements.

What challenges exist for food testing?

Lipids, fiber, waxes, and plant matter can all equate to increased noise and heterogeneity of sample backgrounds. This decrease in signal-to-noise can impact pesticides detection sensitivity and can mask the presence of key and unknown pesticide signatures.

What are the preferred sample preparation and extraction techniques for pesticides testing?

Extraction methods are often essential to remove background noise and maintain detection, while minimizing the loss of sensitivity and range.

QuEChERS extraction, explored further here, benefits from the ability to adapt the method to an array of foods and analysis types. The relatively modern technique, and modifications thereof, has been adopted for use in a number of testing regiments and federally mandated food testing protocols.

Solid phase extraction (SPE), liquid-liquid extractions, and custom techniques are sometimes put into use for select testing scenarios. As an example of the latter, the cannabis industry is witness to new proprietary extraction methods, many of which lack guidelines for testing validation.

How is mass spec analysis of food and plant matrices performed?

LC-MS/MS has affirmed itself as the gold standard platform for pesticides analysis, and is rapidly becoming the preferred analysis technique for mycotoxins and other emerging contaminants. The success of the approach owes to the combination of extreme sensitivity and selectivity to both identify and quantify the large array of compounds in found at varying levels in diverse food matrices.

Targeted analysis by LC-MS/MS has early roots for the detection of relatively well-characterized, known pesticides and their degradation products. As use of the technique escalated, so has the extent of known pesticides spectra and the inclusion of compound species in pesticide spectral library resources.

Multiple-reaction monitoring (MRM) combined with full-scan data capture techniques are now the norm for screening applications. High resolution accurate mass (HRAM) analysis of full-spectrum data coupled with detailed MRM transitions is emerging as the state-of-the-art approach, owing to the wide range of data capture and the specific method of compound ID through well-defined MRM methods. This approach may also safeguard against changing MRLs and pesticides restrictions.

Cannabis pesticides testing presents unique challenges, as state-specific regulations mandate distinct pesticide panels and methods for plant sampling. Fortunately, ongoing development of LC-MS/MS capabilities has meant state-specific testing guidelines are being observed by well-run testing labs. The focus for improvements has now shifted towards sample extraction and ease-of-use for the large variety of testing lab environments.

As far as mass spec detection platforms, triple quadrupole MS is suitable for pesticides detection/quantification within a defined mass range. QTOF MS instruments are used for wide mass range MRM and full-scan data capture application, for enhanced compound discovery and screening using non-targeted methods. GC-MS/MS is applicable to volatile compound analysis, whereas LC and GC can be suitable for known pesticides at increased levels in relatively straight-forward matrices.

Techniques such as CESI-MS can be used for analysis of pesticides and herbicides for which LC-MS/MS is challenged by complex, isomeric, or isobaric degradation products. Glyphosate, a herbicide of increased use and scrutiny, is an example.

Conclusion

The non-targeted LC-MS/MS pesticides analysis approach has complemented and expanded the field of metabolomics. The discovery of degradation products in pesticides can now be compared with normal metabolic products, and effects can be studied in greater detail and metabolic signatures for toxins can be identified. HRAM-MRM techniques, along with enhanced data analysis software, is advancing fields such as phenomics, the study of complete proteome profiling of metabolic processes or diseases. The emerging fields or foodomics and microbiomics represent promising areas for discovery of advanced food profiling and disease diagnostic approaches.

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Updated October 2021