Potentially dangerous contaminants can enter the food chain in a variety of ways – from the inappropriate use of pesticides on crops, to accidental contamination during processing, shipping and storage.
Dioxins are a class of persistent environmental pollutants that can enter the food chain when livestock eat contaminated animal feed. These highly toxic organic compounds, which include polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), are typically generated as byproducts from waste combustion processes or industrial chemical manufacturing processes such as the synthesis of chlorinated pesticides. Dioxins have been labeled as carcinogenic by the United States Environmental Protection Agency (EPA), and present a significant threat to human health even at trace levels.
Because of the health risks posed by dioxins, robust food testing workflows are necessary to ensure these compounds remain below regulatory established safe levels. To identify and quantify these compounds at ultra-low concentrations, sensitive detection technologies are required. Thankfully, the latest instruments are more than up to the job.
Sensitive Analysis of Dioxins in Food by GC-MS/MS
Given the need to determine the presence of dioxins at trace levels in our food, the analytical sensitivity of detection technologies is of particular importance to food testing laboratories and regulatory authorities.
Legislation such as European Union (EU) regulations 2017/644 and 2017/771 outline sampling, sample preparation and analysis methods for the testing of dioxins and other dioxin-like compounds in food and feedstuffs. Prior to 2014, the approved method of detecting PCDDs and PCDFs in food was by gas chromatography-high resolution mass spectrometry (GC-HRMS). However, with recent advances in the sensitivity and selectivity of gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) systems, regulations were updated to include the use of GC-MS/MS for confirmatory analysis to help control maximum levels (MLs) and action levels (ALs) of PCDDs and PCDFs in certain foodstuffs and animal feeds. The latest GC-MS/MS instruments are able to detect these chemicals in complex matrices at ultra-low levels, satisfying stringent safety regulations.
But how sensitive are these systems exactly? To evaluate GC-MS/MS sensitivity in a routine testing environment, we performed confirmatory analysis of PCDDs and PCDFs in solvent standards as well as real feed and foodstuff samples using the Thermo Scientific TSQ 9000 triple quadrupole GC-MS/MS system, equipped with the new advanced electron ionization (AEI) source.
The samples were prepared by a solvent extraction and cleanup step involving an offline multi-layered acidic silica column, which provided the material for the initial performance tests, system calibration and residue quantitation experiments. The mass spectrometer was operated in selected reaction monitoring (SRM) mode, with dwell time priority given to specific transitions of native dioxin and furan congeners.
Traditionally, to assess a GC-MS/MS instrument’s performance under routine testing conditions, peak signal-to-noise ratios are typically calculated, or a series of repeat injections are measured. However, given the high sensitivity of modern GC-MS/MS instruments, which generate very low noise, we calculated the instrument detection limit by defining a method limit of quantitation (LOQ) that could be used to characterize instrument performance for trace analysis of residues in complex matrices.
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GC-MS/MS: Going Beyond Regulatory Requirements for Dioxin Testing
EU regulations require the level of analytical sensitivity to be equal to or less than one fifth of the ML for a specific food or feedstuff. Additionally, criteria for ion ratio tolerance (±15%), the number of transitions (2), and quadrupole resolution (equal or better than unit mass) must also be met. When assessing instrument sensitivity, it is therefore essential that the LOQ is calculated from the lowest concentration point where ion ratios and response factors reliably remain within the permitted EU tolerance levels; the recovery of internal standards and sample intake must also be considered.
Across the 63 injections studied (which included 21 matrix samples, 11 blanks and 31 standard injections) response factors and ion ratios for all native congeners in each sample demonstrated consistent compliance with EU regulations and maintained a high level of sensitivity to meet the required LOQs (Figure 1). The lowest calibration standard amount was adjusted for sample weight and toxicity equivalency factors. Results were five times lower than regulatory requirements, validating the analytical system as not only sufficiently sensitive for routine dioxin testing, but also allowing for user flexibility and variability in sample weight if needed.
The latest GC-MS/MS systems offer exceptional levels of analytical sensitivity and satisfy all EU regulatory requirements for the detection and confirmation of dioxins in food and feed samples. GC-MS/MS is a sensitive, reproducible and robust technique, providing confident results at the lowest quantifiable levels and offering flexibility for users and samples as required. It’s advanced tools such as these that are continuing to help the food testing laboratories protect us from the hidden dangers lurking in the food chain!