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Techniques & Tools Environmental, Gas Chromatography

Fighting Complexity with Simplicity

Dominic Roberts Thermo Fisher in Black and white

Polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are highly toxic, persistent organic compounds that can biomagnify in the environment because of their lipophilic nature. As these chemicals are released through both natural and anthropogenic processes, environmental analysis plays a crucial role in assessing any risk to food chains and, ultimately, to humans. However, measuring PCB and PAH levels in the environment is a complex process that faces two significant challenges. 

First, PCBs and PAHs have similar congener species making them chromatographically difficult to separate. Second, the compounds are found in diverse environmental matrices – from relatively clean water to complex soil and biota samples, which each present their own nuances for accurate determination. Moreover, PCBs and PAHs are toxic even at very low levels, so each predefined compound must be resolved with high sensitivity in these complex matrices.

Typically, laboratories have used GC-MS to analyze environmental samples and quantify PCBs and PAHs. But given the risk of isobaric interference, the need for high sensitivity, and varying matrix complexity, more time-consuming and laborious methods – such as the Soxhlet sample preparation technique – are needed. Worse still, multiple systems are required to determine the separate compounds presented in a sample – even within the PCB and PAH groups, which are likely to represent only one subset of toxins being screened. In other words, multiple methods are needed for each system and sample, which requires highly-trained scientists – not only to operate the equipment but also to review the resulting (complex) data. 

All of these factors add time (40 min per sample is common) and complexity to the analysis – high throughput is not a word associated with PCB and PAH determination. Time is money – and the need for multiple runs per sample also leads to high consumables usage, which further adds to the cost per sample. 

What’s the solution? In short, a new generation of GC-MS technology. Advances in instrumentation solve some current challenges – by enabling selective screening and quantification of targeted and non-targeted compounds in complex matrices – crucially, with minimal method development. More than that, they offer analytical scientists the tools to find hidden toxins that might not be known (or expected) in samples. 

The beating heart of this technology is high resolution accurate mass (HRAM), which can separate matrix interference from target analytes, delivering accurate mass data from a full scan. With high resolving power comes increased analytical selectivity, allowing scientists to determine PCBs, PAHs, and other unknown compounds in a single injection. Higher selectivity also allows simpler sample preparation (for example, QuEChERS) even in complex matrices, saving time. 

In a recent soil analysis study (1), a high-resolution GC-MS was used with simplified QuEChERS sample preparation and predefined methods to identify and quantify PCBs and PAHs. The time taken for sample preparation was decreased by a factor of 20 using this modified QuEChERS method compared to traditional Sohxlet extraction methods.

Today, analytical laboratories are under increased pressure to provide faster and more cost-effective analysis to quantify an ever-increasing number of challenging compounds and increasingly low concentrations. Next-generation GC-HRMS systems – though significantly more expensive than triple quad counterparts – can be more easily justified with their ability to deliver higher laboratory outputs at a lower cost per sample.

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  1. Thermo Fisher Scientific, “Robust analysis of PAHs and PCBs in soil with over 500 repeat injections using Orbitrap Exploris GC” (2021). Available at: https://bit.ly/3wj1dHu.
About the Author
Dominic Roberts

Dominic Roberts, Product Marketing Manager, Thermo Fisher Scientific, UK

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