PolyChlorinated Dibenzo-p-Dioxins (PCDDs) and PolyChlorinated Dibenzo Furans (PCDFs) are two of 12 initial Persistent Organic Pollutants (POPs) that were first proposed by the Stockholm Convention in 2001, and identified by the United Nations Environment Program due to their adverse effects on humans and the ecosystem. These chemicals, collectively called Dioxins, consist of 210 similar compounds (congeners) with different toxicity depending on the number and positioning of chlorine atoms. They are produced as by-products in a number of human activities, such as waste combustion processes or industrial manufacture of chemicals such as chlorinated pesticides.
They are highly toxic, even at trace levels, and can cause cancer, reproductive and developmental problems, and damage to the immune system. Dioxins are ubiquitous in the environment and accumulate in the food chain, mainly in the fatty tissue of animals. More than 90% of human exposure is through food ingestion, mainly meat and dairy products, fish and shellfish. Due to the high toxicity and bio-accumulative nature of dioxins, many national authorities have programs in place to monitor the level of dioxins in the food supply.
Trace Level Dioxin Quantification by GC-MS/MS
Until 2014, European Union (EU) legislation required the confirmation and quantification of PCDDs and PCDFs in food and feed samples to be performed by gas chromatography-high resolution mass spectrometry (GC-HRMS). However, advances in the sensitivity and selectivity of gas chromatography-triple quadrupole mass spectrometry (GC-MS/MS) systems have led to these criteria being updated. The EU now allows GC-MS/MS to be used for confirmatory analysis (as an alternative option to GC-HRMS) to help control maximum levels (MLs) and action levels of PCDDs and PCDFs in certain foodstuffs and animal feeds.
GC-MS/MS platforms utilize highly selective, compound-dependent precursor-to-product ion transitions to obtain confident detection quantification and identification, with little or no interference from other matrix components, but with just sufficient sensitivity. Given the importance of trace level dioxin analysis, analytical sensitivity has been a primary focus for both food safety laboratories and instrument providers. The introduction of a new innovative electron ionization source designed for Advanced Electron Ionisation (AEI) has resulted in substantial improvements in signal to noise, increased confidence in results for measurement of dioxins at EU regulatory levels. These improvements are described in an Application Note titled: Routine, regulatory analysis of dioxins and dioxin-like compounds in food and feed samples.
This application note describes the extensive experiments undertaken for the development of a sample-to-results Dioxin Analyzer suitable for the routine, robust analysis of large numbers of samples across a wide variety of sample types, and requiring minimum maintenance. The Chromeleon CDS software automatically calculates the results as WHO Toxic Equivalency Factors (TEQs) in pg/g fat, reducing errors and improving productivity. For an overview of the new Dioxin Analyzer watch a video sound byte from Pittcon 2019.
The performance of the Thermo Scientific™ TSQ™ 9000 Triple Quadrupole GC-MS/MS system equipped with the new Advanced Electron Ionization (AEI) source was evaluated for the analysis of PCDD/Fs in solvent standards and food/feedstuff samples. We used the comprehensive integrated workflow to produce results, which were fully compliant with EU regulations.
The target compounds are extracted using the Thermo Scientific™ASE™ (Accelerated Solvent Extraction) 350 System. The ASE 350 uses organic solvents at elevated temperatures and pressures to increase the efficiency of the extraction process. The result is faster extraction times and a significant reduction in solvent use and lower disposal costs. Then the sample extraction was cleaned up using an offline multi-layered acidic silica column step and the PowerPrep™ automated system (FMS Inc.) with a three-column set (multi-layered ABN silica, basic alumina, and carbon columns). The final extract volume and solvent was 10 μL of nonane.
Acquisition, data calculation, and reporting were automatically performed on Thermo Fisher Chromeleon Chromatography Data System (CDS). Chromeleon CDS includes specific tools to streamline the complexities of the calculations required to process and report data using isotopic dilution.
The method, with minor modification, was validated by the China National Center for Food Safety Risk Assessment (CFSA) in solvent standard and food sample, and also validated by our China Customer Solution Center (Food & Beverage) in solvent standard (EDF-5544, CIL, UK) and QC sample. In the validation, the sample is first freeze-dried, ground and then spiked with known concentrations of C13 labeled internal standard. The target compounds are extracted using the Thermo Scientific™ Scientific™ ASE™ (Accelerated Solvent Extraction) 350 System. Clean-up was performed by a fully automated sample purification system equipped with a three-column set (multi-layered ABN silica, basic alumina, and carbon columns). The final extract volume and solvent was 20 μL of nonane, added with internal standard and analyzed on the TSQ 9000 GC-MS/MS with Chromeleon CDS.
The validation experiment generates good results in terms of GC resolution, linearity, ion ratio, sensitivity, and repeatability, all in line with EU regulations. All samples were analyzed in parallel on the Thermo Scientific™ DFS™ Magnetic Sector GC-HRMS, considered the reference standard for dioxin analysis. The results were consistent with the results obtained using the DFS.