2.6. Determination of the presence of dioxin-like compounds using H4IIE-luc bioassay
Briefly, 10 g of each sediment sample was extracted using pressurized liquid extraction (PLE), using n-hexane as extraction solvent, at a temperature of 150 °C and three static cycles of 15 min. An aliquot of the extract was cleaned up on a column, filled with 10 g of 10 percent deactivated silica and 1 cm of Na2SO4 on the top. Another aliquot of the extract was purified on a multilayer column, designed to eliminate all the labile compounds, prepared as follows: 30 percent KOH silica, 5 percent neutral silica, 30 percent H2SO4 (40 percent) silica, 15 percent H2SO4 (20 percent) silica, 10 percent neutral silica and 10 percent Na2SO4. Eluates were evaporated into 50 µl in DMSO. All samples were analysed following the guidelines developed by Olsman (2005). Dose–response curves were performed for the extracts and TCDD using a sigmoidal dose–response (variable slope) curve fitting equation (GraphPad Prism® 4.0). Bio-TEQs were calculated from the dose–response curves by relating the luciferase induction potency of the samples to that of the positive reference TCDD.