This International Standard specifies a method for the determination of tetra to hepta- Dioxin-likepolychlorinated Biphenyls (PCBs) in waters and waste waters (containing less than 1 % suspended solids) using high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS). The method is optimised for Dioxin-like PCBs, but may include other co-planar compounds such as Polychlorinated Dioxins and Furans (PCDDs/PCDFs), Polychlorinated Naphthalenes (PCNs) and Polychlorinated Diphenylethers (PCDEs). This method may be used to determine Dioxin-like PCBs in other matrices (e.g. biota, sediments, air), however additional cleanup steps and technique