How PFAS are detected in water and soil — the analytical methods, why testing is hard, and where detection technology is heading.
Per- and polyfluoroalkyl substances (PFAS) are among the most scrutinized contaminants in environmental work today, and among the hardest to measure. The regulatory limits are set in parts per trillion, the compound family runs to thousands of members, and the sampling equipment itself can contaminate the sample. This article covers how PFAS are detected, which EPA methods apply to which media, where the numbers go wrong, what the newer screening tools add, and what to do once PFAS turn up on a site where Hepure’s customers work.
Nearly all regulatory PFAS analysis rests on one pairing. High-performance liquid chromatography (HPLC) separates the compounds in a water, soil or tissue extract; tandem mass spectrometry (LC-MS/MS) then identifies each compound by its mass and fragmentation pattern and quantifies it against a known standard. Modern methods use isotope dilution, spiking the sample with labeled versions of the target compounds so that losses during extraction are corrected automatically.
The strength of the approach is breadth and sensitivity: it resolves dozens of individual PFAS, including the most studied ones, PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate), at single-digit parts per trillion. The limitation is that it only finds the compounds it is told to look for. A target list of 25 or 40 compounds is a small slice of a family that numbers in the thousands.
| Method | Media | Analytes | Notes |
|---|---|---|---|
| EPA 537.1 | Drinking water | 18 PFAS | The original compliance method; solid-phase extraction then LC-MS/MS. |
| EPA 533 | Drinking water | 25 PFAS | Adds short-chain compounds; isotope dilution. Used alongside 537.1 for the national drinking-water rule. |
| EPA 1633 | Groundwater, surface water, wastewater, soil, sediment, biosolids, leachate, tissue | 40 PFAS | Finalized in 2024; the method for site investigation and remediation samples. |
| SW-846 8327 | Non-potable water | 24 PFAS | Direct injection, faster and cheaper, but detection limits in the tens of ppt. |
| Draft 1621 (AOF) | Wastewater | Total adsorbable organic fluorine | A screening number, not a compound list; flags fluorine the targeted methods miss. |
For a remediation site the usual answer is Method 1633 for groundwater and soil, with 537.1 or 533 reserved for samples that will be compared to drinking-water standards. Confirm with the laboratory and the regulator before sampling; a result generated by the wrong method can be rejected for compliance purposes.
Sensitivity. Many PFAS are present at parts-per-trillion concentrations, and the federal limit for PFOA and PFOS is 4 ppt. Reporting limits near that number demand clean instruments, rigorous blanks and careful extraction. A laboratory’s reporting limit is worth asking about before you send samples; a 10 ppt reporting limit cannot demonstrate compliance with a 4 ppt standard.
Selectivity. With thousands of distinct PFAS, each with different chain lengths and functional groups, isolating specific compounds in the presence of others is difficult, and co-extracted substances can interfere. Branched and linear isomers of the same compound complicate quantification further.
Cost. The instruments are expensive, the analysis is slow, and it requires trained analysts. Routine, dense monitoring is a real budget line, which is one reason screening methods are gaining ground.
The sample. PFAS are everywhere, including in the gear used to collect them. PTFE-lined caps and tubing, waterproof field notebooks and clothing with stain-resistant coatings, some sunscreens and insect repellents, and low-density polyethylene bottles have all contaminated samples. Laboratories supply certified bottles (typically HDPE or polypropylene) and sampling protocols for a reason. Field blanks, equipment blanks and trip blanks are not optional at the ppt level; without them, a low-level detection cannot be distinguished from a sampling artifact.
Targeted LC-MS/MS misses two things that matter on remediation sites. The first is precursors: polyfluorinated compounds that are not on the list but transform in the environment, or in a treatment system, into the regulated perfluoroalkyl acids. The total oxidizable precursor (TOP) assay addresses this by oxidizing a sample under controlled conditions and re-analyzing it; the increase in PFOA, PFOS and their relatives after oxidation reveals the hidden precursor mass. A site whose targeted results look modest can carry several times that mass as precursors, which matters for sizing an adsorption remedy.
The second is everything else. Total organic fluorine (TOF) and adsorbable organic fluorine (AOF) methods burn the sample and measure the fluoride released, giving a single number for all organofluorine present. They cannot say which compounds are there, but a large gap between the AOF result and the sum of targeted compounds is a signal that the target list is not telling the whole story.
Detection technology is moving on two fronts. High-resolution mass spectrometry (HRMS) with non-target and suspect screening can identify PFAS that have never been on a method list, by matching exact masses and fragmentation patterns against libraries; it is a research and forensic tool today and is finding its way into source attribution work. At the other end, field-deployable sensors, including biosensors that use enzymes or antibodies to bind specific PFAS and produce a measurable signal, promise rapid, low-cost screening at the wellhead. None has yet replaced laboratory LC-MS/MS for a compliance decision, but as screening tools they can tell a project where to spend its laboratory budget.
PFAS do not degrade in the environment, so monitoring is how a site learns where they are, how they move and where they accumulate. That record drives the risk assessment, guides the remedy, and is the only evidence that source controls and treatment are working. The stakes rose in 2024: EPA finalized the first national drinking-water limits for PFAS, 4 ppt each for PFOA and PFOS, and designated PFOA and PFOS as hazardous substances under CERCLA, which brings them into site investigations and liability in a way they were not before. In 2025 EPA announced that it would keep the PFOA and PFOS limits, extend the compliance deadline to 2031, and reconsider the limits set for four other PFAS; the rulemaking on that reconsideration was still in progress as of this writing. Standards this strict make sensitive, defensible detection, and a plan for what to do when PFAS are found, more important than ever.
Detection is step one; treatment is where Hepure comes in. We supply the activated carbon that most PFAS remedies are built on: injectable Fluxsorb RC colloidal carbon for in situ adsorption zones that arrest a plume in the aquifer, and CarbPure TRA powdered activated carbon, certified to NSF/ANSI 61, for water treatment. Learn more on our PFAS Solutions page or review current PFAS remediation techniques.
Two ways to get started: call 866-727-4776 to discuss your project, or send us your sampling results and site assessment for review.