PFAS Water Testing Lab

Water (“PFAS”) analysis in the lab typically follows a multi‑step workflow, which can be broken down into:

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## 1. Sample Collection & Preservation

* **Grab sampling** in pre‑cleaned, PFAS‑free high‑density polyethylene (HDPE) or polypropylene bottles to avoid contamination.
* **Field filtration** (e.g. 0.45 µm) if you want to separate dissolved vs. particulate‑associated PFAS.
* **Acidification** (to pH < 2 with LC‑MS‑grade formic or acetic acid) and refrigeration (4 °C) to slow microbial activity and adsorption losses.

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## 2. Internal Standards & Quality Controls

* **Isotopically-labelled PFAS standards** (e.g. ^13C‑PFOA, ^13C‑PFOS) are spiked into each sample at known concentrations. These track recoveries through extraction and correct for matrix effects in the mass spectrometer.
* **Field blanks**, **laboratory blanks**, and **matrix spikes** accompany every batch to check for contamination, carryover, and extraction efficiency.

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## 3. Extraction & Concentration

Most methods use **Solid‑Phase Extraction (SPE)**:

1. **Conditioning**: SPE cartridges (often weak anion exchange) are pre‑rinsed with methanol, then water.
2. **Loading**: Up to 1 L of water is passed slowly (\~5 mL/min) through the SPE sorbent, which binds PFAS.
3. **Washing**: A weak aqueous rinse to remove salts and interferences.
4. **Elution**: PFAS are desorbed with a small volume (e.g. 5–10 mL) of methanol or methanol/ammonium hydroxide.
5. **Concentration**: The eluate is evaporated under a gentle nitrogen stream and reconstituted in a small volume (e.g. 1 mL) of 50:50 water\:methanol for analysis.

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## 4. Instrumental Analysis

### Liquid Chromatography–Tandem Mass Spectrometry (LC‑MS/MS)

* **Separation** on a C18 or PFAS‑optimized column (e.g. polymeric phase) using a water/methanol (or acetonitrile) gradient.
* **Detection** in negative electrospray ionization (ESI−) mode, monitoring specific precursor → product ion transitions for each PFAS (MRM mode).
* **Quantification** by comparing the peak area ratios (analyte vs. labelled standard) against a calibration curve prepared in matrix‑matched standards.

### Gas Chromatography (GC‑MS)

* Used for volatile or derivatized PFAS (e.g. fluorotelomer alcohols), but less common for the “classic” perfluoroalkyl acids.

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## 5. Data Processing & Reporting

* **Method detection limits (MDLs)** and **limits of quantitation (LOQs)** are established from replicate analyses of low‑level spikes.
* **Recoveries** of internal standards must fall within an acceptable window (often 70–130%).
* DWPFAS concentrations are typically reported in ng/L (ppt) for each individual PFAS.

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## 6. Advanced & Complementary Techniques

* **Total Oxidizable Precursor (TOP) assay**: oxidizes precursor compounds to terminal PFAS (e.g. PFOA/PFOS) to estimate the “hidden” PFAS burden.
* **Particle‑bound PFAS analysis**: acid digestion of filter solids followed by SPE.
* **High‑resolution MS (HRMS)**: for non‑targeted screening of novel or unknown PFAS structures.

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### Common Standard Methods

* **EPA 537.1** (drinking water; 18 analytes by SPE + LC‑MS/MS)
* **EPA 533** (non‑drinking waters; broader suite)
* **ASTM D7979** (industrial waters; LC‑MS/MS)

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**In practice**, you’ll adopt the method best suited to your sample matrix, target analyte list, and required detection limits. But at its core, PFAS analysis in water hinges on:

1. Rigid contamination control
2. Efficient extraction/concentration (SPE)
3. Clean, sensitive LC‑MS/MS quantitation
4. Robust QA/QC with isotopic standards

This workflow ensures you can reliably detect even parts‑per‑trillion levels of these “forever chemicals.”