Development and validation of a method for analyzing polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in sewage sludge samples

A method has been developed for the analysis of polychlorinated dibenzo- p-dioxins (PCDD) and dibenzofurans (PCDF) in sewage sludge samples. It was found that PCDD/F are best Soxhlet extracted from the matrix with toluene for 24 h, after having tested other solvents (dichloromethane and hexane/acetone 41/59) and other extraction times. Several dean up steps (sulfuric acid, multilayer silica and Florisil columns) and concentration are required prior to analysis of the extract by high resolution gas chromatography-high resolution mass spectrometry (HRGC-HRMS). The complete procedure has been validated and the accuracy and precision data (repeatability and reproducibility) are given. The method is linear in the range studied and the limit of detection ranges between 0.2 and 2.2 pg g^-1 of dry matter for the 2,3,7,8-substituted congeners. Moreover, the suitability of the method has been checked in an international interlaboratory comparison. The successful application of this method to several samples from Catalan and Dutch urban wastewater treatment plants was demonstrated.