ISO 25101:2009

Overview

ISO 25101:2009 specifies a validated analytical method for the determination of the linear isomers of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) in unfiltered water samples. The standard targets drinking water, ground water and surface water (fresh and sea water) and combines solid‑phase extraction (SPE) sample preparation with high‑performance liquid chromatography–tandem mass spectrometry (HPLC‑MS/MS) for selective, sensitive quantification. The method reports other isomers separately as non‑linear isomers where applicable.

Key topics and technical requirements

• Analytes and scope
  • Linear PFOS and PFOA are the primary analytes. Non‑linear isomers may be reported separately.
  • Typical working ranges: PFOS 2.0 ng/L to 10 000 ng/L; PFOA 10 ng/L to 10 000 ng/L. Higher concentrations (100–200 000 ng/L) can be accommodated after dilution or reduced sample size.
• Sample handling
  • Use inert, non‑fluoropolymer sample bottles; avoid glassware for sampling to prevent adsorption losses.
  • If free chlorine is present, add a dechlorinating agent (e.g., sodium thiosulfate).
  • Store at (4 ± 2) °C and analyse within two weeks or freeze with verified stability.
• Solid‑phase extraction (SPE)
  • Copolymer‑based SPE sorbents are recommended (typical cartridges contain 150–250 mg sorbent).
  • Conditioning sequence and careful wetting of sorbent are required; extraction is performed on unfiltered (whole) samples.
• Instrumental analysis
  • Separation by HPLC followed by tandem mass spectrometry (MS/MS) for selected precursor → product ion monitoring.
  • Annex D describes limited use with single MS; Annexes A–C give sorbent, column and chromatogram examples.
• Quality control
  • Use 13C‑labelled internal standards (e.g., 13C‑PFOA, 13C‑PFOS).
  • Check for matrix effects (ion suppression/enhancement), especially in seawater and wastewater.
  • Avoid fluoropolymer contamination in instrument plumbing and vial caps; procedural blanks should be substantially lower than expected sample concentrations.

Applications and users

ISO 25101:2009 is used for:

• Regulatory compliance testing and environmental monitoring of PFOS/PFOA in water.
• Drinking‑water utilities, environmental laboratories and contract testing labs.
• Research institutions, consultants and regulatory agencies performing occurrence, fate and risk assessments.
• Situations requiring trace‑level quantification of perfluoroalkyl substances (PFAS) in unfiltered waters.

Keywords: ISO 25101:2009, PFOS, PFOA, perfluorooctanesulfonate, perfluorooctanoate, HPLC‑MS/MS, solid phase extraction, water quality, unfiltered samples.

Related standards

• ISO 3696 (Water for analytical laboratory use)
• ISO 5667‑1 (Sampling - guidance on sampling programmes)
• ISO 8466‑1 (Calibration and evaluation of analytical methods)