Per- and polyfluoroalkyl substances (PFAS) are a growing concern for environmental and public health, but their analysis can be hindered by complex sample matrices and stringent regulatory requirements. Solid-phase extraction (SPE) is a targeted enrichment technique that can help laboratories overcome these obstacles, enabling faster and more accurate detection and quantification of PFAS. In this article, we'll examine the role of SPE in streamlining PFAS analysis, including optimized protocols, advanced cartridge technologies, and guidance on best practices for your laboratory.
Why use SPE for PFAS analysis?
In SPE, specific compounds are isolated from complex samples by passing a liquid sample through a cartridge filled with a solid material that selectively retains target analytes. This process removes interfering substances, which significantly improves analytical accuracy and sensitivity. The modular cartridge design allows for efficient handling, scalability, and easy integration into laboratory workflows. As a result, SPE is widely used in fields ranging from environmental monitoring to public health.
PFAS are difficult to detect due to their chemical properties and the low concentrations at which they are often found. SPE addresses these challenges by efficiently isolating and concentrating PFAS from complex environmental and biological samples. This technique enhances the sensitivity and accuracy of detection methods, such as liquid chromatography–tandem mass spectrometry (LC-MS-MS), by removing interfering substances and ensuring that even trace levels of PFAS can be detected. For instance, SPE has been successfully employed to concentrate PFAS in drinking water to part-per-trillion levels, as demonstrated through triple-stage quadrupole mass spectrometry.1
Sorbents for SPE: Tailoring the approach
The effectiveness of SPE in PFAS analysis largely depends on the choice of sorbent material. When the PFAS targets are known, cartridges can be selected with specific sorbents such as C18 (a hydrophobic, non-polar sorbent) for non-polar PFAS or WAX (weak anion exchange) for capturing anionic PFAS, ensuring maximum retention and selectivity. For unknown target screening, where a broad range of PFAS needs to be captured, versatile polymeric sorbents are used to provide comprehensive coverage.
PFAS are difficult to detect due to their chemical properties and the low concentrations at which they are often found.
Dual-phase cartridges, such as those combining carbon and WAX, offer an advanced solution for complex matrices. The carbon phase focuses on removing organic contaminants, effectively cleaning up the sample, while the WAX phase captures anionic PFAS. This combination makes dual-phase cartridges ideal for challenging situations where multiple PFAS types need to be isolated and interfering substances minimized, such as those encountered in soil and sludge analysis.2
Online vs offline SPE: Choosing the right workflow
With advancements in SPE technology, laboratories now have the option to choose between online and offline SPE systems, each with its own benefits. Offline SPE involves manually processing samples through cartridges before analysis, offering flexibility and control over each step of the process. It’s well-suited for low-throughput environments or when specific, tailored methods are required for different sample types.
Online SPE, on the other hand, integrates SPE directly with LC-MS-MS analytical instruments, automating the sample preparation process. This approach minimizes manual handling, reduces the risk of contamination, and significantly improves reproducibility and throughput. Online SPE is particularly valuable for high-throughput labs and regulatory monitoring programs where consistency and real-time analysis capabilities are crucial. Recent studies, such as those involving the analysis of short-chain PFAS in water, have demonstrated the efficacy of online SPE approaches.3
Applications of SPE in PFAS analysis
SPE is versatile enough to be applied across a wide range of environmental and biological matrices. Here’s how it’s used across different fields:
Water: SPE is widely used to analyze PFAS in drinking water, groundwater, and surface water. EPA methods such as Method 533, 537.1, and the newly released 1633 rely on SPE for extracting PFAS from water samples before LC-MS-MS analysis. These methods are essential for regulatory compliance and monitoring water quality, ensuring that even low levels of PFAS are detected.
Air: In air sampling, SPE is employed to concentrate PFAS from both indoor and outdoor environments.4 Passive air samplers with integrated SPE cartridges can capture volatile and semi-volatile PFAS over time, making it possible to monitor air quality and assess the potential for PFAS exposure through inhalation.
Soil and sludge: SPE is crucial in the analysis of PFAS in soil and sludge, where these compounds can persist for extended periods. EPA Method 8327 outlines procedures for using SPE to prepare soil and sludge samples for PFAS analysis, helping to identify contamination hotspots and assess the long-term environmental impact.
Food: SPE is increasingly used in the analysis of PFAS in food items, where these contaminants can accumulate through environmental exposure. Recent advances, including the application of QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) extraction methods typically used for pesticide analysis, have shown promise in PFAS studies.5
SPE is versatile enough to be applied across a wide range of environmental and biological matrices.
Biological tissues: SPE is also used to analyze PFAS in biological tissues, such as blood, liver, and other organs. Specialized sorbents are chosen to handle the high lipid content and complex composition of these samples, ensuring that PFAS can be accurately quantified despite the challenging matrix.6
Indoor dust: SPE is employed in the extraction of PFAS from indoor dust samples, which can accumulate from household products. This application is important for assessing human exposure to PFAS in indoor environments, particularly in homes and workplaces.
Distilling insight from information with SPE
SPE sharpens the focus on PFAS detection, transforming a challenging process into a reliable path for analysis. By stripping away the noise from complex samples, SPE equips scientists with clear, actionable data. As PFAS regulations tighten, SPE will be indispensable in meeting stricter standards, driving innovation in contamination detection, and ensuring that even the smallest traces of these persistent chemicals are effectively managed.
References:
- “Triple-stage quadrupole mass spectrometer to determine ubiquitously present per- and polyfluorinated alkyl substances in drinking water at part per trillion levels using solid phase extraction approach”. Bulletin of Environmental Contamination and Toxicology, 110(1), 32 - December 2022. https://doi.org/10.1007/s00128-022-03686-1
- “Method for extraction and analysis of per- and poly-fluoroalkyl substances in contaminated asphalt”. Analytical Methods, 14(17), 1678-1689 - May 2022. https://doi.org/10.1039/d2ay00221c
- “Fast analysis of short-chain and ultra-short-chain fluorinated organics in water by on-line extraction coupled to HPLC-HRMS”. Science of The Total Environment, 943, 15 September 2024, 173682. https://doi.org/10.1016/j.scitotenv.2024.173682
- “A review of sample collection and analytical methods for detecting per- and polyfluoroalkyl substances in indoor and outdoor air”. Chemosphere, 358, 142129 - April 2024. https://doi.org/10.1016/j.chemosphere.2024.142129
- “Comparison and validation of the QuEChERSER mega-method for determination of per- and polyfluoroalkyl substances in foods by liquid chromatography with high-resolution and triple quadrupole mass spectrometry”. Analytica Chimica Acta, 1230, 340400 - September 2022. https://doi.org/10.1016/j.aca.2022.340400
- “Less is more: a methodological assessment of extraction techniques for per- and polyfluoroalkyl substances (PFAS) analysis in mammalian tissues”. Analytical and Bioanalytical Chemistry, 415(24), 5925-5938 - August 2023. https://doi.org/10.1007/s00216-023-04867-5