Detection of PCBs in natural waters by front face fluorometry on solid sorbent on account of their fluorescence quantum yields and interaction with humic substances

A method for the detection of PCBs in natural water, based on extraction/concentration with tab shaped elements cut from C18 fiber glass SPE disks coupled with a fluorescence detection has been evaluated. The potential of the method was estimated through the measurement of the fluorescence quantum yields in acetonitrile and limits of detection (LOD) of 11 PCBs congeners and Arochlors 1221 and 1242 in pure water. Most of the LOD values are within the range of PCB concentrations found in highly polluted waters (<1microg l(-1)) and thus confer some interest to the method. However, as expected, naturally present humic substances was shown to compete with the solid phase for PCBs adsorption thus reducing the capability of the method when applied to natural waters. A Stern-Volmer plot of the fluorescence signal reduction in the presence of various type of humic substances leads to apparent sorption coefficients (K(DOC)) significantly higher than the literature values determined for PCBs or for polycyclic aromatic hydrocarbons, indicating that besides complexing PCBs, humic substances may also block some of the adsorption sites at the sorbent surface. An increase of the pH up to 11 was shown to reduce the negative effect of humic substances but their preliminary total denaturation or destruction appears as a prerequisite condition for taking full advantage of the present method.