GC-MS and the Art of POP Analysis
Persistent organic pollutants (POPs) encompass a wide variety of contaminants, but they share one thing in common: they have the potential to hit headlines and cause huge disruption to the food and feed industry. Fortunately, innovation does not stand still – and advances in mass spectrometry are opening up new vistas in POPs analysis. Here, I assess the complete range of GC-MS techniques used in POPs analysis, including the latest GC-MS instrument developments.
Esteban Abad Holgado |
sponsored by Thermo Fisher
I gave a presentation at the 10th International Symposium on Recent Developments in POPs Analysis, held in Prague, Czech Republic, earlier this year (you can see that presentation here: tas.txp.to/0116/Holgado). Why was I there? Essentially, to expand on an investigation that we presented at the 19th International Mass Spectrometry Conference in Kyoto, Japan, in 2012. Back then, we wanted to demonstrate some new ideas of utilizing mass spectrometry for the determination of dioxins in environmental and food samples. In particular, our project looked at the suitability of gas chromatography-tandem mass spectrometry (GC-MS/MS) for the analysis of dioxin-like persistent organic pollutants (dl-POPs). In Kyoto, we compared GC-MS/MS to the reference technique of GC-high-resolution (HR)MS – but the world of mass spectrometry moves very quickly indeed. Here, I share our work with the latest systems.
A short lesson
First, let me quickly go over the key groups of compounds that we are particularly interested in when it comes to POPs analysis:
i) Organochlorine pesticides (for example, Aldrin, Chlordane, DDT, Dieldrin, Endrin, Heptachlor, Hexachlorobenzene, Mirex and Toxaphene). Despite many of these compounds being banned, they remain a problem. ii) Polychlorinated biphenyls (PCBs). PCBs have many uses, including dielectric and coolant fluids in electrical apparatus, cutting fluids for machining operations, and in heat transfer fluids. iii) Dioxins. Despite also occurring naturally, dioxins are anthropogenic substances that get into the environment.
Why are we so concerned? Well, when these substances enter the food and feed chain, they generally hit the headlines as international scale incidents. There will be few of you who do not recall the scandal of dioxin contamination hitting the Belgian poultry industry back in 1999. And as recently as 2008, Italy had to recall mozzarella cheese products, while Ireland recalled pork products. The silver lining is that such failures in the food chain tend to trigger a positive response; for example, the global Stockholm Convention on POPs, and the EU’s introduction of not only new regulations and limits, but also recommended protocols for sampling and analysis.
Reacting to new technology
Europe Commission Regulation (EU) No 252/2012 specified that GC-HRMS should be used for confirmatory dioxin analysis in food and feed, while GC-MS/MS was permitted as a screening technique. Jump forward to today and Commission Regulation (EU) No 589/2014 specifies the use of either GC-HRMS or GC-MS/MS for confirmatory dioxin analysis in food and feed, recognizing “technical progress and developments” in GC-MS/MS. Notably, the regulation does state that GC-MS/MS is “an appropriate confirmatory method for checking compliance with the maximum level”, whereas GC-HRMS remains the recommended technique for “determination of low background levels in food monitoring, following of time trends, exposure assessment of the population”. In short, this means Magnetic Sector HRMS has been recognized as delivering superior sensitivity, as required for low-level background studies. Additionally, Magnetic Sector GC-HRMS fulfills all requirements for all types of dioxin applications, and is considered the reference standard for dioxin analysis.
The EU regulations for food & feed have specific requirements for GC-MS/MS confirmatory methods.
i) You must monitor at least two specific precursor ions, each with one specific corresponding transition product ion, for all labeled and unlabeled analytes.
ii) There is a maximum permitted tolerance of relative ion intensities of ±15 percent for selected transition product ions compared with calculated or measured values (the average is taken from calibration standards), applying identical MS/MS conditions, in particular collision energy and gas pressure.
iii) The resolution for each quadrupole is to be set equal to or better than unit mass resolution (unit mass resolution: sufficient resolution to separate two peaks one mass unit apart).
iv) For the limit of quantification (LOQ), the method must demonstrate that it is able to distinguish between the blank and cut-off value. A notification level needs establishing for samples that respond below this level.
v) For polychlorinated dibenzodioxins/polychlorinated dibenzofurans (PCDD/PCDFs), the limits of detection (LOD) should be in the higher femtogram range (10–15 g). For most PCB congeners, it is sufficient to set LOQ in the nanogram range (10–9 g). However, to measure congeners similar to dioxin-like PCBs (in particular non-ortho substituted congeners) the lower limit of the working range must reach the lowest picogram (10–12 g).
In terms of workflow, Magnetic Sector GC-HRMS and GC-MS/MS are similar, following the same preliminary stages of sample preparation, extraction (manual or automated) and cleanup before analysis and finally calculating the toxicity equivalency (TEQ).
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