Frank L. Dorman explores performance-based analytical methods for dioxin analysis
New guidance from the United States Environmental Protection Agency (US EPA) has recognised the use of atmospheric pressure gas chromatography (APGC) with tandem quadrupole mass spectrometry (MS) as an acceptable alternative to traditional high-resolution magnetic sector MS for US EPA Method 1613B in the identification and quantification of polychloro-dioxin/furans in environmental matrices.
SGS AXYS Analytical Services led the two-year effort that resulted in the US EPA’s approval of the alternative test procedure (ATP) – the SGS AXYS Method 16130. The current EPA 1613B dioxin testing method has long been considered the gold standard, but it relies upon magnetic sector instruments that are becoming less available and supported, necessitating the development of a new test. In collaboration with Waters, SGS AXYS performed a series of studies that compared the performance of traditional magnetic sector MS to tandem quadrupole MS before submitting the necessary data for the ATP request.
Here we discuss the analytical advances in dioxin analysis and the road to validating the new method.
What are Dioxins?
Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) are a group of chemically related compounds, known as persistent organic pollutants (POPs), that are extremely toxic, persistent, and bioaccumulative environmental contaminants. These compounds arise mainly from human activity such as waste incineration and certain industrial activities. Analysis of chlorinated dioxins and furans is required to: ensure industrial emissions meet regulatory standards; track sources of ongoing emissions; monitor the food supply; identify contaminated sites; provide input into risk assessments; and contribute to human health assessment by measuring body burdens.
However, due to their presence in trace amounts, highly sophisticated and sensitive analytical systems that provide very low thresholds of detection are required to measure them.
Decades of Analytical Advances
Gas chromatography mass spectrometry (GC-MS) has been the mainstay of dioxin analysis for many years. This technology improved the low detection limits and problems with specificity experienced with electron capture detection (ECD) and GC prior to the 1970s but requires intensive front-end chemistry to separate trace analytes from potential interferences in complex environmental matrices. Advances in chromatographic separations helped to address the need to determine isomer-specific concentrations of dioxins and furansusing high-resolution capillary GC (HRGC). This was one of the first steps that enabled relatively inexperienced analysts to conduct dioxin measurements.
Following the 1999 dioxin crisis in Belgium and the Stockholm Convention for POPs in 2001, the European Commission implemented an official continuous control strategy for food and feed. At the time, no standardised methods for food were available, but GC coupled with (magnetic sector) high resolution mass spectrometry (GC-HRMS) was widely accepted as the most sensitive and selective tool, especially in comparison with other MS analysers such as time-of-flight (TOF).
The Move to MS/MS
Despite the benefits of high resolution, magnetic sector instruments require a high degree of expertise and are expensive, limiting their widespread use. Between the 1970s and 2000s, tandem quadrupole MS, also known as MS/MS, gradually rose in popularity for a variety of quantitative applications. Recent technological developments in GC-MS/MS have spurred the revision of the European Commission specific criteria and led to the US EPA’s evaluation of atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS) as a new, alternative method for dioxin analysis.
The development and validation of Method 16130 by SGS AXYS with Waters and others, recognises its performance similarities with GC-HRMS, and evaluation results show equivalency in terms of sensitivity, linearity, selectivity, accuracy and precision, with more simplified operation.
Validating the Method
The GC-MS/MS method was developed and validated using the Waters Xevo TQ-XS APGC-MS/MS, which uses atmospheric pressure chemical ionisation with nitrogen gas. The atmospheric pressure source results in less fragmentation and therefore provides more sensitivity than an electron ionisation (EI) source due to the enhanced amount of molecular ion. The Xevo TQ-XS tandem quadrupole mass spectrometer is a high-performance system optimised for high sensitivity and specificity, combined with a wide linear dynamic range even at high acquisition rates.
As well as establishing operating protocols and meeting quality assurance/quality control (QA/QC) specifications for the technique for PCDD/PCDF analysis, it was important that the new, alternative method could produce accurate data for real world samples with complex sample matrices.
Nine different samples of four matrices (wastewater, biosolid, sediment, and tissue) were analysed and a comparison of HRMS and MS/MS for the 36 samples showed excellent agreement.
The results of this method validation study, submitted as an ATP to the US EPA, have met the Method 1613B specifications for PCDD and PCDF analysis. Under SGS AXYS Method 16130, the APGC Xevo TQ-XS mass spectrometer is an accepted alternative technology for dioxin analysis, meaning that environmental labs are now able to leverage this APGC-MS/MS system for routine, highly sensitive testing with improved robustness.
The Waters APGC-MS/MS technology is already in use by Canadian and European researchers, commercial labs and government agencies for dioxin/furan analysis, as well as for other POPs analyses. For labs in the USA, the US EPA’s approval means that the APGC-MS/MS methodology meets all the quality control criteria of magnetic sector-based methods, has the potential to lower costs for laboratories and their customers, and potentially expands the number of labs that may be able to provide testing.
The Future Management of Dioxins
Acceptance of the SGS AXYS Method 16130 is a significant step forward in recognising the value of performance-based analytical methods and it will translate to increased sensitivity and robustness in the laboratories performing dioxins and other POPs analysis.
The development of this alternative method frees laboratories to deploy modern instrumentation that is less expensive, more sensitive and easier to operate, enabling food and environmental labs to make increasingly sensitive measurements from complex samples. The unique collaboration between Waters, SGS AXYS and the US EPA makes an important contribution to the ongoing development of dioxin analysis methods and is crucial to monitoring contaminant levels in the food chain and ensuring the food we consume, and our environment, are safe.
Frank L. Dorman is senior principla environmental market manager at Waters