Due to their chemical and physical properties, per- and polyfluorinated alkyl substances (PFAS) have been extensively used in a wide variety of industrial applications since the 1940s. These exclusively anthropogenic compounds are present in commercial products ranging from industrial polymers to stain repellents to fire-fighting aqueous film-forming foams — the main source of PFAS in the environment. They are also used in the production of fabrics, food packaging and household products. Given their widespread use, PFAS are ubiquitous in most environments, but their levels are especially elevated in areas around airports, landfills, wastewater treatment plants or in the aftermath of fires.
PFAS are persistent, they bioaccumulate in the body, and are highly water-soluble, which aids their dispersal into sources of drinking water. As a result of their properties and prevalence in industrial applications, these substances build up in both the environment and our bodies and take a long time to break down, earning them the nickname of ‘forever chemicals.’ The potential health implications of exposure to PFAS are significant, with concerns rising over PFAS’ impact on growth, immunity, fertility, endocrine function and an individual's likelihood of developing cancer. There is, therefore, a pressing need to detect PFAS precisely and reliably in drinking water, to ensure that consumers are protected from any associated adverse health effects.
Essential Efforts to Keep Drinking Water Safe
The US Environmental Protection Agency (EPA) advises maximum permissible levels for both individual and total PFAS in drinking water (EPA 537/537.1 and 533). At the same time, additional guidelines either exist or are in development for other waters, sediment, and soil extracts (EPA 8327 and ASTM 7979). In the US, EPA is working to pass regulatory limits. The proposed national maximum contaminant levels (MCLs) for the 18 PFAS compounds are those covered by EPA Method 537.1 and are set at 70 parts per trillion (ppt) in drinking water [1]. However, individual states adhere to lower MCLs down to 10 ppt.
Performing PFAS analysis to assure compliance with such guidelines is challenging. The analysis must be sensitive at trace levels (low ppt) to accurately characterize PFAS. As there are over 6,000 such compounds, many PFAS and precursors lack standard reference materials and/or cannot be accounted for by existing analytical methods. As a result of both these challenges and the significant potential of PFAS to negatively impact the health of the public and the environment, there is a need for a single analytical workflow for direct determination of as many PFAS as possible. Advanced liquid chromatography-tandem mass spectrometry (LC-MS/MS) has emerged as a leading tool in drinking water analysis, used in conjunction with automated solid-phase extraction (SPE) and combustion ion chromatography (CIC).
Accurate PFAS Analysis with Automated SPE and LC-MS/MS
Published in March 2020, EPA Method 537.1 (version 2.0) defines a method to determine up to 18 PFAS in drinking water using LC-MS/MS with SPE for sample preparation.
SPE offers a rapid and selective way to prepare samples for chromatographic analysis. Most testing laboratories perform SPE manually using a vacuum manifold, which can process multiple samples simultaneously. However, this manual approach brings additional difficulties. It is labor-intensive, and analysts must dedicate uninterrupted time and effort to complete an extraction. The quality of extraction is highly dependent on the technique used, bringing inconsistency. This is partly due to the need to control the flow rate through the cartridge, and at some steps, the cartridge must not run dry – an arduous task. Additionally, different manifold housings and cartridge loadings are required at each step of the SPE process, adding yet more time-consuming work for the operator.
These challenges can be minimized with automation. In line with EPA guidelines, automated SPE combined with LC-MS/MS is a technique of choice for PFAS analysis in water. Advanced technology exists to facilitate this methodology and has been used to develop and demonstrate an analytical method for PFAS determination [2]. The Thermo Scientific Dionex AutoTrace 280 PFAS Solid-Phase Extraction system, for instance, uses positive pressure to deliver a constant flow rate and ensures cartridges do not run dry. It improves the reliability and consistency of analysis and allows for unattended operation.
Automated SPE systems produce extractions that are accurate, reproducible and remove error-prone manual steps. The system flow paths are composed of non-fluoropolymer based materials, preventing the sample from being contaminated during the extraction process.
It is essential to minimize background interference, which can arise from solvents, reagents, containers, and the instrument itself, to achieve low system background levels as per EPA requirements. Low background levels are prerequisites to enable the sensitivity and precision needed to ensure interference-free analyte identification or quantitation. Automated SPE showed good accuracy (with relative standard deviations of <10%) and good recovery (70–130%), which is according to the requirements outlined in US EPA 537.1.
Introducing automated SPE into LC-MS/MS workflows saves time and effort, improves the quality of analytical results, and lowers the risk of needing to re-run a sample. This results in higher laboratory throughput, further enhanced by the parallel processing abilities of advanced and automated systems.
Characterizing Numerous PFAS with CIC and LC-MS/MS
Regulation is growing more stringent for a range of PFAS, chlorinated and brominated organics, and adsorbable organically bound halogens (AOX). There is, therefore, a pressing need to directly determine as many environmentally relevant fluoroorganic compounds and precursors as possible – within a single analytical workflow.
To increase the number of PFAS analyzed, laboratories can use automated CIC. In a CIC workflow, the organic components are first adsorbed on activated carbon. After a rinsing step to remove inorganic halides, the samples are oxidized at elevated temperatures (~1000 °C) using hydropyrolysis. Volatile products are automatically absorbed and subsequently detected as sulfates or halides, e.g., fluoride from PFAS, by ion chromatography (IC).
CIC can be used to analyze a larger number of halogenated compounds in a non-targeted approach. These include the organic halogen contaminants that are generated during water treatment processes. CIC instrumentation, such as the Thermo Scientific Dionex ICS-2100 Reagent-Free Ion Chromatography (RFIC) system linked to a combustion device, analyzes halogen-containing compounds such as PFAS with good precision and recovery [3].
Alongside drinking water, CIC can be used to determine PFAS as a parametric value in surface water, groundwater, and wastewater, safeguarding the health of anyone exposed to such water sources. CIC enables the extraction and determination of more sample components than other methods that use a specified set of PFAS for evaluation. The concentrations of PFAS found by CIC are higher than those obtained by targeted, highly selective LC-MS/MS. The procedure covers fluoroorganic compounds that are not readily determined by LC-MS/MS. Therefore, automated CIC approaches can enhance the analytical abilities of PFAS testing laboratories by extending their capabilities beyond the characterization of small subsets of compounds, allowing them to remain competitive in a fast-paced industry.
Conclusion
PFAS are prevalent in the environment and pose a significant risk as a human health hazard. Precise determination of PFAS in drinking water is, therefore, of high priority, with several national and international standardization and regulatory bodies developing methods specifically to analyze aqueous samples.
When used in combination with advanced LC-MS/MS technology, automated SPE and CIC offer a range of valuable benefits for PFAS analysis in water. Automated SPE improves the reliability, consistency and efficiency of PFAS analysis while reducing the risk of manual error and increasing throughput. CIC, on the other hand, extends the analytical LC-MS/MS toolset to cover a more comprehensive range of potential contaminants. Both SPE and CIC can be easily and cost-effectively integrated into existing PFAS workflows to improve and extend the detection and characterization of these compounds in water samples – an essential step towards protecting consumer safety and safeguarding water quality.
References
[1] Shoemaker, J. and Dan Tettenhorst (2020) Method 537.1 Determination of Selected Per- and Polyflourinated Alkyl Substances in Drinking Water by Solid Phase Extraction and Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS). US Environmental Protection Agency, Washington, DC.
[2] Qiu, C., Zhang, X., Ullah, R., Chen, W. and Liu, Y. (2020) Determination of per- and polyfluorinated alkyl substances (PFAS) in drinking water using automated solid-phase extraction and LC-MS/MS. Thermo Scientific Application Note 73346.
[3] Von Abercron, E., Neist, U., Klocke, I., Georgii, S., and Brunn, H. (2020) AOF by combustion IC – non-targeted complemental determination of PFAS in aqueous samples. Thermo Scientific Application Note 73481.
About the Author
Chris Shevlin is a Product Marketing Manager for Ion Chromatography systems at Thermo Fisher Scientific. Chris started his career in a pharmaceutical QC laboratory running HPLC and other chromatographic methods. After earning an MBA in 2004, Chris has worked in sales, product management and marketing with a few of the major analytical instrument manufacturers. In 2015, Chris joined Thermo Fisher selling chromatography and automated sample preparation systems in the northeastern US.
In 2019, Chris moved into a product marketing role with the Ion Chromatography and Automated Sample Preparation business unit. Chris’s entire career has been focused on chromatography, first as a chemist in the laboratory, then with Thermo Fisher doing sales and now as a marketing manager. This experience has helped Chris to have an in-depth understanding of the challenges analytical laboratories face and how to improve their workflows and processes.