Spectroscopic Detection of Water Pollution

The pollution of water by oil, gasoline or other pollutants is unfortunately increasing. Several spectroscopic techniques have been developed to measure the concentration of specific pollutants. These techniques are not only helpful in tracing the polluting source, but they can also initiate measures against the pollution. 

Often the absorption spectra of several pollutants overlap. It is therefore not possible to determine the specific concentrations of different pollutants from a single absorption measurement at a given wavelength A. Either several well-selected excitation wavelengths Aj have to be chosen (which is time consuming for in situ measurements) or time-resolved fluorescence-excitation spectroscopy can be used. If the excited states of the different components have sufficiently different effective lifetimes, timegated fluorescence detection at two or three time delays Atj after the excitation pulse allows a clear distinction between different components. 

This has been demonstrated by Schade [15.79], who measured laser-induced fluorescence spectra of diesel oil and gasoline, excited by a nitrogen-laser at A = 337.1 nm. Time-resolved spectroscopy exhibits two different lifetimes that are determined by measuring the intensity ratio of the LIF in 

Often the combination of spectral and temporal resolution is helpfiil to simultaneously determine the individual concentrations of the different components in a mixture of pollutants, even if their absorption spectra overlap. An example is the pollution of water by different types of oil. In Fig. 10.25a the transmission curves of three different oil sorts (Diesel oil, gasoline and heavy oil) are shown and in Fig. 10.25b their emission spectra, while Fig. 10.25c shows the decay curves of the different sorts. Such measurements can help to find the polluter. In Fig. 10.26 the total fluorescence spectrum of a mixture of different aromatic hydrocarbons is shown together with the contributions of the different components, obtained by the different detection techniques discussed above [1481]. 

This was demonstrated by Schade [1482], who measured laser-induced fluorescence spectra of diesel oil and gasoline, excited by a nitrogen laser at X = 337.1 nm. Time-resolved spectroscopy exhibits two different lifetimes that are determined by measuring the intensity ratio of the LIF in two different time windows (Fig. 10.25). This time-resolved spectroscopy increases the detection sensitivity for field measurements. Mineral-oil pollutions of 0.5 mg/1 in water or 0.5 mg/kg in polluted soil can be detected [1482]. Using photoacoustic spectroscopy with a dye laser, concentrations down to 10 -10 mol/1 of transuranium elements could be detected in 

When a laser beam is vertically incident on the ocean surface the refraction and inclination of the reflected beam gives information on the momentary slope of the water surface at the point where the laser beam hits the surface. Rapid scanning of the laser over a certain area allows to determine the momentary amplitudes and frequencies of water waves and gives a detailled picture of the wave spectrum. Spectral resolution of the reflected light provides previously unobtainable information on the 

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Analytical needs and opportunities in this area are challenging, particularly for pollutants of emerging concern such as endocrine disrupting compounds and pharmaceutical derivatives. Direct spectroscopic measurements of the sort than can be used for atmospheric measurements are not usually applicable. Sample collection, preparation, and analysis typically have been carried out in separate steps. Consequently, the development of techniques for in situ measurement capability, remote sensing and detection, and sensors for monitoring in soil and water would afford significant progress. 

In heterogeneous photocatalysis experiments, especially in reactions dealing with water detoxification and gaseous pollutant removal, the disappearance of target chemicals, the degree of mineralization of total organic carbon (TOC), and the reaction intermediates can be detected by spectroscopic optical methods (UV-vis and IR), TOC measurements, and chromatographic analysis. 

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