Determination of Per- and Polyfluoroalkyl Substances (PFAS) Concentration: Principles, Methods, and

Per- and polyfluoroalkyl substances (PFAS), often described as "forever chemicals," are a large family of synthetic fluorinated compounds whose environmental persistence and potential health risks have triggered strict regulatory limits worldwide. Accurate determination of PFAS concentrations in water, soil, consumer products, and biological matrices is therefore essential for regulatory compliance, environmental monitoring, and product safety assurance. This article provides a comprehensive technical overview of PFAS testing samples, target analytes, analytical methods, quality control requirements, and typical application scenarios.

Technical Overview

Per- and polyfluoroalkyl substances (PFAS) are a class of more than 4,000 man-made chemicals characterized by fully or partially fluorinated carbon chains. The extremely strong carbon–fluorine bond imparts exceptional thermal stability, chemical inertness, and water- and oil-repellency, which explains their widespread historical use in firefighting foams, non-stick coatings, food-contact materials, textiles, semiconductor processing, and surface treatment agents. However, these same properties make PFAS highly persistent in the environment and capable of bioaccumulation, with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) being the most extensively studied representatives.

PFAS concentration determination is analytically challenging for several reasons. Target compounds exist at trace levels (often ng/L or μg/kg), the family includes carboxylic acids, sulfonic acids, telomers, precursors, and volatile species with divergent physicochemical behavior, and the ubiquitous presence of fluoropolymers in laboratory equipment creates a persistent background contamination risk. Modern PFAS analysis therefore relies on isotope-dilution liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) as the workhorse technique, supported by gas chromatography for volatile species and total-fluorine screening approaches for broader coverage. Internationally recognized frameworks such as ISO 25101, ISO 21675, ASTM D7979, ASTM D7968, and the United States EPA Methods 533, 537.1, and 1633, together with Chinese national standards including the GB/T and GB 31604 series, define validated procedures for extraction, quantification, and quality control.

Testing Samples

Environmental Water Samples

Drinking water, groundwater, surface water, seawater, wastewater, and landfill leachate represent the largest volume of PFAS testing demand. Regulatory limits such as single-digit ng/L advisory levels require extremely low detection capability. Samples are collected in HDPE or polypropylene containers with PP-lined caps, avoiding PTFE-lined closures, and are typically preserved at 4 °C without chemical dechlorination unless free chlorine is present.

Soil, Sediment, and Sludge

Solid environmental matrices are screened for legacy PFAS contamination near industrial sites, airports, and firefighting training areas where aqueous film-forming foams (AFFF) were deployed. Samples are air-dried or freeze-dried, homogenized, sieved, and extracted by alkaline digestion or methanol/sonication according to ASTM D7968 or EPA Method 1633.

Consumer Products and Food-Contact Materials

Paper and board food packaging, non-stick cookware coatings, water-repellent textiles and apparel, carpets, leather, cosmetics, and semiconductor wet-process chemicals are tested against restrictions in regulations such as the EU POPs Regulation and EU food-contact legislation, as well as national requirements like China's GB 31604 series for migration of PFOA and PFOS from food-contact materials.

Biological and Human Samples

Serum, plasma, whole blood, urine, breast milk, fish tissue, and shellfish are analyzed for biomonitoring programs and food-safety surveillance, where protein-rich matrices require specialized cleanup and isotope-dilution quantification to compensate for matrix effects.

Air and Emission Samples

Ambient air, workplace atmospheres, and stack emissions are sampled on sorbent tubes or filters to quantify volatile precursors such as fluorotelomer alcohols (FTOHs), fluorotelomer olefins, and perfluorinated acid amides.

Testing Items

Depending on regulatory scope and client objectives, testing portfolios range from a small regulatory list to a comprehensive multi-analyte panel. Typical targets include:

• Perfluoroalkyl carboxylic acids (PFCAs): PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnDA, PFDoDA, PFTrDA, PFTeDA
• Perfluoroalkane sulfonic acids (PFSAs): PFBS, PFHxS, PFHpS, PFOS, PFNS, PFDS
• Perfluoroalkyl sulfonamides and telomer sulfonates, including FOSA and NEtFOSA precursors
• Fluoroether replacement chemistries: HFPO-DA (GenX), ADONA, and related short-chain ether acids
• Fluorotelomer alcohols (4:2, 6:2, 8:2, 10:2 FTOH) and fluorotelomer acrylates for volatile and precursor assessment
• Polyfluoroalkyl phosphate esters (PAPs: 6:2, 8:2 monoPAP and diPAP) in food-contact paper and cosmetics
• Sum parameters: total organic fluorine (TOF), extractable organic fluorine (EOF), adsorbable organic fluorine (AOF), and total oxidizable precursor (TOP) assay results

Testing Methods

Liquid Chromatography–Tandem Mass Spectrometry (LC-MS/MS)

LC-MS/MS with negative-mode electrospray ionization and multiple reaction monitoring (MRM) is the reference technique for ionic PFAS. Chromatographic separation employs reversed-phase C18 or dedicated fluorinated-phase columns with ammonium acetate–modified water/methanol gradients. Quantification is performed by isotope dilution using mass-labeled internal standards (for example, 13C4-PFOA and 13C8-PFOS), which correct for extraction losses, matrix suppression, and instrumental drift. Method detection limits in reagent water commonly reach 0.1–2 ng/L, fulfilling the strictest drinking-water thresholds.

Sample Preparation for Aqueous Matrices

Drinking water methods such as EPA 537.1 and EPA 533 use solid-phase extraction (SPE) on weak anion-exchange (WAX) cartridges with carboxylic acid preservatives, followed by methanol/ammonium hydroxide elution. Direct injection or "dilute-and-shoot" approaches (for example, EPA Method 8327) trade some sensitivity for speed and are adequate for higher-concentration samples. ISO 25101 and ISO 21675 follow comparable SPE protocols validated for PFOA/PFOS and extended PFAS lists, respectively.

Sample Preparation for Solids and Biological Matrices

Soils, sediments, and biosolids are extracted by alkaline digestion (sodium hydroxide in methanol), oscillation, or sonication per ASTM D7968 and EPA 1633, followed by SPE cleanup and carbon or graphitized sorbent cleanup to remove humic and lipid interferences. Tissues are often enzyme-digested or extracted with acetonitrile followed by dispersive SPE (dSPE) cleanup. Food-contact migration testing uses food simulants (for example, 10%, 20%, and 50% ethanol in water, or iso-octane for fatty foods) defined by food-contact frameworks such as the GB 31604 series, with the resulting simulants analyzed by LC-MS/MS.

Gas Chromatographic Methods

Volatile neutral PFAS such as FTOHs, sulfonamides, and acrylates are determined by GC-MS after solvent extraction or thermal desorption, frequently with derivatization and negative chemical ionization (NCI) to achieve low-picogram sensitivity in air and dust samples.

Total-Fluorine and Screening Approaches

Where exhaustive PFAS coverage is required, combustion ion chromatography (CIC) measures adsorbable or extractable organic fluorine (AOF/EOF), providing an upper-bound indicator of PFAS burden without compound identification. Instrumental neutron activation, particle-induced gamma emission (PIGE), and X-ray fluorescence (XRF) serve as rapid total-fluorine screens on polymers and consumer articles. The TOP assay oxidizes precursors to measurable perfluoroalkyl acids, revealing otherwise invisible precursor reservoirs.

Quality Assurance and Contamination Control

Rigorous QC is indispensable because PTFE-containing components in autosampler vial caps, HPLC tubing, and solvent lines can contaminate samples at ng/L levels. Best practice includes using polypropylene labware, installing an in-line delay column before the injector, analyzing method blanks and field blanks with every batch, monitoring surrogate and internal-standard recoveries, verifying calibration linearity and continuing calibration verification, and confirming reporting limits against regulatory thresholds. Accredited third-party laboratories operating under ISO/IEC 17025 management systems routinely participate in interlaboratory proficiency schemes to demonstrate comparability.

Applications

• Drinking-water compliance monitoring against national limits and health advisories for PFOA, PFOS, PFHxS, PFBA, and HFPO-DA
• Site investigation and remediation verification at former fluorochemical plants, military installations, and AFFF-affected airports
• Wastewater and biosolids discharge monitoring under industrial pretreatment and effluent programs
• Product conformity assessment for food-contact paper, coatings, textiles, and electronics against EU, North American, and GB market-access requirements
• Supply-chain due diligence and restricted-substance screening driven by consumer-brand stewardship commitments
• Human biomonitoring and epidemiological studies quantifying serum PFAS burdens
• Food-safety surveillance of fish, shellfish, dairy, and drinking water in the farm-to-table chain
• Occupational exposure assessment in fluorochemical manufacturing and metal-plating workplaces
• Environmental forensics distinguishing contamination sources through congener fingerprinting

FAQ

What is the difference between targeted PFAS analysis and total-fluorine screening?

Targeted analysis quantifies a defined list of individual PFAS compounds (commonly 20–70 analytes) with compound-specific isotopically labeled standards, delivering low-ng/L sensitivity and regulatory defensibility. Total-fluorine methods such as CIC, PIGE, or XRF measure the aggregate fluorine signal and capture both known and unknown organofluorine species, but they are less sensitive, cannot identify individual compounds, and may include fluorine from innocuous polymeric sources. The two approaches are complementary: screening flags potential non-compliance, while targeted LC-MS/MS confirms identity and concentration.

Why do some laboratories report higher PFAS levels after a TOP assay?

The total oxidizable precursor (TOP) assay chemically oxidizes polyfluoroalkyl precursors—compounds not detected by standard targeted methods—into perfluoroalkyl carboxylic and sulfonic acids that are then quantified. When pre-oxidation and post-oxidation results are compared, the increase reveals the hidden precursor pool, which can represent a substantial fraction of total PFAS at AFFF-impacted or textile-treated sites.

What detection limits can be achieved for PFAS in water?

With SPE preconcentration and modern triple-quadrupole LC-MS/MS, method detection limits of roughly 0.1–2 ng/L for individual legacy PFAS are routinely achievable in reagent water, comfortably below current drinking-water limits in most jurisdictions. Matrix-rich samples such as wastewater may exhibit higher detection limits due to dilution requirements and ion suppression, which is why isotope dilution and matrix-matched calibration are standard practice.

How are PFAS contamination risks during sampling and analysis controlled?

Field and laboratory teams avoid all fluoropolymer materials: samples are collected in polypropylene or HDPE bottles with unlined caps, PTFE tape and waterproof labels are prohibited at the sampling point, and laboratory plumbing is modified to replace PTFE tubing with PEEK or stainless steel. An isolator/delay column placed between the LC pump mixer and the injector retains system-derived PFAS background, and batch blanks verify that contamination remains below reporting thresholds.

Which standards govern PFAS testing?

Key frameworks include ISO 25101 and ISO 21675 for water, ASTM D7979 for water and solids by LC-MS/MS, ASTM D7968 for soil, EPA Methods 533, 537.1, 8327, and 1633 for aqueous and multi-matrix analysis, and the GB 31604 series for food-contact migration testing in China. Selecting the appropriate method depends on the matrix, target analyte list, and the regulatory jurisdiction against which results will be assessed.