Monitoring of fluorescent and nonfluorescent aromatics in waste water by rapid cyclohexane extraction and fluorometric detection: first measurements

摘要

Abstract: Recently a new fluorescence method has been introduced applying two different signals: (1) the conventional fluorescence CF occurring at short path-lengths of the exciting radiation in the fluids, and (2) the multi-path saturation fluorescence MPSF originating at long path-lengths, which can be achieved by multi-path reflection cells, where the exciting radiation is fully absorbed by the fluid. This method considers both fluorescent as well as nonfluorescent substances. The ratio between CF and MPSF yields the total absorption. First experiments were performed to investigate this method for in-situ monitoring of aromatic substances in waste water. For this purpose samples of a waste water plant near Berlin were extracted with cyclohexane within 5 minutes in a first step yielding extracts with a waste water matrix. Then polycyclic aromatic substances were added directly to the cyclohexane extracts. The fluorescence CF and MPSF were measured at different excitation wavelengths in the UV part of the spectrum using a lab-standing experimental setup as well as a portable device. Synchronously, the conventional absorption of each sample was determined by an optical multi- channel analyzer. Regression analyses between the fluorescence ratio MPSF($lambda$-1$/)/MPSF($lambda$-2$/) and substance concentration yielded squared correlation coefficients r$+2$/ higher than these of conventional absorption spectrometry. Thus, the MPSF method is more accurate than the conventional absorption leading to lower detection limits. The MPSF method is obviously able to detect fluorescent and nonfluorescent aromatic hydrocarbons in cyclohexane extracts of waste water without further sample pre-treatment. Thus dangerous and harmless samples could be discriminated in field measurements. !9