Laboratory Testing of Online Extraction of Organic Contaminants from Water - Optimization of Online Extraction Concept
MetadataShow full item record
Real-time monitoring of the freely dissolved concentrations of PAHs in the aquatic environment is important in order to limit adverse effects on aquatic organisms. It is the freely dissolved fraction of the total concentration that is the most environmentally relevant concentration. Measuring only the freely dissolved concentrations can be challenging with regular water sampling methods. Passive samplers effectively sample the freely dissolved concentrations, but require exposure to the water over several weeks in order to produce good samples. In situ fluorometry can provide with frequent real-time measurements of PAHs in the field, but interference from other fluorescent compounds can be a problem with no separation measures. A new method that combines the passive sampler materials selectivity for freely dissolved hydrophobic contaminants and in situ fluorometry is tested as a possible online PAH sensor. Laboratory testing of the method was carried out to optimize the system for this purpose. 80 cm silicone tubing is coiled around a metal mesh cylinder and immersed in a water sample. The water sample were spiked with a predetermined amount of PAHs. The PAHs partition from the water phase and into the silicone tubing and diffuses through a tube wall. A solvent is pumped through the tubing, extracting PAHs from the inner face of the silicone tube. The solvent extracts are pumped directly into a fluorescence spectrometer and analyzed by fluorometry. The system was calibrated for four different PAHs; Naphthalene, fluorene, phenanthrene. Fluorene were measured successfully down to 1.8 ng/l, which indicated that the system is able to detect environmentally relevant concentrations. Testing of the system were carried out with PAH-16 mixes, diluted produced water and contaminated sediments. Most of the tests were performed with a nonpolar solvent (heptane) while three tests were carried out with a polar solvent (methanol). The results from these tests indicate that nonpolar solvent does not increase the extraction efficiency. Comparing the test results to analysis of the samples in a GC-MS showed that the method effectively can detect and quantify PAHs in single component mixtures. good matches for the phenanthrene samples as well as for the calculated phenanthrene and fluorene concentrations in the PAH-16 samples. The calculated concentrations in the produced water samples were a lot higher than the PAH-concentrations found with the GC-MS. This is because the concentrations were estimated without adjusting for interference from other fluorescent compounds in the sample. Further work on the calibration and interpretation is necessary.