The Ubiquity of PFAS
PFAS are not merely a scientific curiosity; they represent a pervasive environmental challenge. Their "forever" nature, attributed to the strong carbon-fluorine bond, means they don not readily break down, leading to accumulation in the environment and living organisms. This persistence, combined with their ability to travel long distances through air and water, has resulted in global contamination (Malatji et al., 2023). From the depths of the ocean to the peaks of remote mountains, PFAS are found in virtually every corner of the planet. The presence of PFAS in drinking water, food, and even human blood underscores the urgent need for accurate and reliable analytical methods. This ubiquity makes accurate analysis a daunting task, as background contamination can easily skew results, leading to misinterpretations and potentially flawed conclusions.
Deep Dive into Background Interference: Sources and Mechanisms
Accurate detection of PFAS is akin to finding a needle in a haystack, especially when the haystack itself is contaminated. Common sources of PFAS contamination in the lab include Teflon-coated materials, certain plastics, solvents, reagents, dust, airborne particles, and even clothing. These contaminants can leach from materials, adsorb from air, or cause cross-contamination during sample handling, significantly impacting analytical results. For example, using non-PFAS-free labware can introduce trace levels of these chemicals, leading to false positives or inflated measurements. The mechanisms of contamination are diverse:
- Leaching: PFAS can migrate from polymer-based labware (e.g., PTFE, FEP) into solvents and samples.
- Adsorption: Airborne PFAS can adsorb onto surfaces, including glassware and analytical instruments.
- Cross-contamination: Improper handling and cleaning procedures can transfer PFAS from contaminated surfaces to clean samples.
Understanding these contamination mechanisms is the first line of defense in minimizing background interference. Implementing strict laboratory protocols, such as using dedicated PFAS-free systems and equipment, is crucial for maintaining data integrity.
A Focus on Measurement Modes and Sample Preparation
Liquid Chromatography-Mass Spectrometry (LC/MS) and Gas Chromatography-Mass Spectrometry (GC/MS) are the cornerstone analytical techniques employed for the identification and quantification of PFAS in diverse sample types. LC/MS, particularly when coupled with tandem mass spectrometry (LC-MS/MS), has become the preferred method due to its high sensitivity and versatility in analyzing a broad spectrum of ionic and polar PFAS compounds found in aqueous and solid matrices. This technique excels in separating PFAS molecules based on their chemical properties using liquid chromatography, followed by highly sensitive and selective detection using mass spectrometry.
GC/MS, on the other hand, is less commonly used for PFAS analysis because of the thermal stability required for some of these compounds. However, it plays a crucial role in the analysis of volatile PFAS, often requiring specific sample preparation techniques such as Solid Phase Micro Extraction (SPME) to facilitate their introduction into the gas chromatograph. Derivatization techniques can also be employed to make certain PFAS amenable to GC analysis.
Therefore, the choice between LC/MS and GC/MS is largely dictated by the specific PFAS analytes of interest and the characteristics of the sample matrix. In many cases, a comprehensive PFAS analysis strategy may involve the complementary use of both techniques to cover a wider range of compounds.
Importance of Sample Preparation and the Challenge of Background Contamination
The analysis of PFAS using LC/MS and GC/MS necessitates effective sample preparation techniques to achieve the required sensitivity and accuracy.
Online SPE offers an automated and efficient approach for sample enrichment and cleanup, particularly for aqueous matrices, minimizing solvent use and contamination. LLE and SLE serve as fundamental extraction methods for liquid and solid samples, respectively, though they may require additional cleanup steps.
SPME, including the advanced SPME Arrow, is invaluable for the analysis of volatile PFAS amenable to GC/MS, offering a solvent-free and simplified workflow.
QuEChERS provides a rapid and cost-effective method for extracting PFAS from complex matrices like food, often coupled with dSPE (or uSPE) for enhanced cleanup.
Micro-SPE cartridges represent a miniaturized SPE format, offering benefits such as reduced solvent consumption and potential for automation across various applications. Each of these techniques has its own set of principles, applications, advantages, and limitations that must be carefully considered based on the specific analytical goals and sample characteristics.
Below you can explore each sample preparation method in more detail. You will also find ways of automating them.
(online) - SPE
Automated extraction linked directly to LC/MS, minimizing manual steps and contamination risk. Ideal for aqueous samples, enhancing sensitivity.
Online SPE integrates extraction and cleanup with LC/MS, using cartridges or columns to retain PFAS, wash away interferences, and elute directly into the LC column. This automation reduces human error and solvent use, while concentrating analytes for improved detection limits. It is used for drinking water, environmental samples, and food extracts.
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LLE and SLE
LLE uses solvent partitioning, SLE uses solvent leaching from solids. Both are basic extraction methods, often needing further cleanup.
LLE separates PFAS based on solubility in immiscible liquids, while SLE extracts PFAS from solids into a solvent. Both methods are foundational but can be labor-intensive and may co-extract interferences. LLE is used for aqueous, SLE for solid matrices like soil, requiring optimization and often, SPE cleanup.
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SPME
Solvent-free extraction using coated fibers, ideal for volatile PFAS and GC/MS. Simplified, reduces contamination, especially with SPME Arrow technology.
SPME extracts PFAS onto a coated fiber, which is then thermally desorbed into a GC/MS. Primarily for volatile PFAS, it eliminates solvents and simplifies sample prep. The SPME Arrow enhances sensitivity. Applications include water and food contact materials, offering a complementary method to LC/MS for volatile compounds.
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Micro-SPE Cartridges
Miniaturized SPE, reducing solvent and sample use. Automatable, enhances sensitivity. Various sorbents for selective PFAS retention.
Micro-SPE cartridges offer miniaturized SPE, reducing solvent and sample volumes. They are designed for automation and use various sorbents like C18 and WAX for selective PFAS retention. This method enhances sensitivity through analyte concentration and is applicable in food safety and environmental monitoring, providing an efficient alternative to traditional SPE.
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The selection of the most appropriate sample preparation technique for PFAS analysis should be guided by several factors, including the nature of the sample matrix (e.g., water, soil, food, air), the specific PFAS analytes of interest (considering their volatility and polarity), the required sensitivity for detection, and the available analytical instrumentation (LC/MS or GC/MS).
Background PFAS contamination poses a significant challenge to accurate and reliable analysis due to the ubiquitous nature of these compounds and the low levels at which they are often monitored. Contamination can be introduced at any stage, from sample collection through laboratory analysis, originating from sources such as sampling equipment, personal protective equipment, sample containers, laboratory consumables, reagents, and even the analytical instruments themselves. The presence of background PFAS can lead to false positives and inaccurate quantification, especially when analyzing at trace levels. Therefore, implementing rigorous strategies to minimize contamination is of paramount importance in PFAS analysis.
Learn more about PFAS analysis and PFAS-free consumables to reduce your background noise.
References
Malatji, N., Mpupa, A., & Nomngongo, P. N. (2023). Poly- and per-fluoroalkyl substances in water: Occurrence, analytical methodologies, and remediations strategies: A comprehensive review. Reviews in Analytical Chemistry.
Rankin, K., Mabury, S. A., & Jenkins, T. M. (2020). A review of the occurrence and treatment of emerging per-and polyfluoroalkyl substances (PFAS) in drinking water. Journal of Hazardous Materials, 385, 121513.
Explore more of our application notes, webinars and poster via the Content Hub
Advancing PFAS Analysis - Robotic Automation and Streamlined LC/MS Workflows
To support the scientific community and advance PFAS analysis we are proud to offer a webinar on this topic.
Key topics:
- PFAS Fundamentals: Learn about the chemistry and significance of PFAS compounds.
- Sample Preparation Challenges: Understand current hurdles, regulations and best practices in PFAS extraction and purification.
- Automated LC/MS Workflows: Get an overview on automated workflows and see how PAL System integrates with LC/MS to optimize sample preparation and injection.
- Deep Dive: Explore online SPE for PFAS analysis.
Equip your PAL System for PFAS Analysis
Measuring PFAS is challenging due to their persistence, complex chemical nature, and presence at extremely low levels (parts per trillion) in environmental samples. Rigorous sample preparation, advanced analytical instrumentation, and robust quality control are essential for reliable PFAS quantification.
PAL System focusses on PFAS-free tubing, tools, and modules enabling:
- Fully automated workflows
- Specialized LC/MS tools
- Multi valve setups for increased productivity using online SPE
- μSPE clean-ups for miniaturized workflows
High-Sensitivity PFAS Determination in Seafood
This application note showcases a fully automated workflow for the precise quantification of 73 PFAS in seafood. Utilizing a PAL RTC autosampler and Agilent triple quadrupole LC/MS system (LC/TQ), the method automates calibration, QuEChERS extraction, and μSPE clean-up.
