IMEP-23 is linked to the Water Framework Directive (WFD). It studied the capability of control laboratories to measure the eight WFD PAHs in the presence of humic acid in a water matrix. Humic acid simulates natural colloidal organic matter and is known to adsorb PAHs. This gives rise to various issues that are of large importance for the control laboratories.
Participants' results were benchmarked against the IMEP certified reference values. On average 80 % of the z scores was satisfactory. Zeta scores were calculated for those laboratories who provided an uncertainty estimate. These were less satisfactory and this shows that many laboratories encounter difficulties to provide a reasonable uncertainty estimate.JRC.D.4-Isotope measurement
