ISO 28540:2011 — Determination of 16 Polycyclic Aromatic Hydrocarbons (PAH) in Water by GC-MS

Introduction to ISO 28540

ISO 28540:2011, developed by ISO/TC 147/SC 2, specifies a GC-MS method for the determination of 16 selected polycyclic aromatic hydrocarbons (PAHs) in drinking water, groundwater, and surface water. The method achieves detection limits of 0.005 µg/L for drinking and groundwater, and 0.01 µg/L for surface water. Many PAHs are known or suspected carcinogens, and regulatory limits exist in numerous countries. These compounds are byproducts of incomplete combustion and are found in fossil fuels, making them ubiquitous environmental contaminants.

The 16 Priority PAH Analytes

The standard targets 16 PAHs ranging from naphthalene (2 rings) to indeno[1,2,3-cd]pyrene (6 rings). These compounds share fused aromatic ring structures and exhibit varying degrees of toxicity, environmental persistence, and bioaccumulation potential. The 16 compounds are on the US EPA priority pollutant list and are monitored worldwide under the Water Framework Directive and similar regulations. PAHs with higher molecular weight tend to be more carcinogenic but less water-soluble, creating distinct analytical challenges.

Analytical Method Principle

PAHs are extracted from water samples by liquid-liquid extraction using hexane as the extraction solvent. An isotopically labelled internal standard mixture is added before extraction to correct for recovery losses. The extract is concentrated by evaporation under a gentle nitrogen stream and redissolved in an appropriate solvent such as toluene or acetonitrile. GC separation uses a fused silica capillary column with a non-polar or slightly polar polysiloxane stationary phase. The column must be capable of resolving benzo[a]pyrene from benzo[e]pyrene — a critical separation requirement given that these two isomers have very different toxicological properties. Detection is by mass spectrometry using electron impact ionization (EI) in selected ion monitoring (SIM) mode, which provides the sensitivity and specificity needed for trace-level quantification.

Calibration and Quantification

Calibration is performed using standard solutions covering the expected concentration range. Internal standard quantification corrects for recovery losses and instrument variability. The injection standard, added just before GC-MS injection, monitors instrument response drift. Identification relies on retention time matching and ion ratio confirmation against known standards. At least two diagnostic ions per compound are monitored in SIM mode for confident identification.

Engineering Design Insights

The practical challenges of PAH analysis at trace levels are considerable. PAHs are ubiquitous in the laboratory environment — they are present in solvents, on glassware, and even in the air of urban laboratories. Effective blank control is essential. The standard’s requirement for extracting samples within a defined holding time reflects the fact that PAHs can adsorb to container walls, volatilize (especially naphthalene), or undergo photodegradation when exposed to UV light. Sample preservation techniques including the addition of sodium thiosulfate to quench residual chlorine and storage at 4 °C in amber glass bottles are critical for sample integrity.

For laboratories implementing this method, a dedicated PAH-free workspace with UV-blocking lighting and strict solvent purity requirements is not a luxury — it is a necessity for achieving the method detection limits. Method validation should include recovery studies, precision assessment, and measurement of uncertainty.

Frequently Asked Questions