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Conventional fluorescence methods are usually applied for the detection of fluorescent substances. A simple technique taking into account nonfluorescent substances has been introduced applying two different signals: (i) the linear or conventional fluorescence (CF) occurring at relatively short path-lengths of the exciting radiation in the fluids, and (ii) the multi-path saturation fluorescence (MPSF) originating at long path-lengths, as in multi-path reflection cells, where the radiation is fully absorbed by the fluid. A relation between the fluorescence signals and the absorption coefficients of fluorescent and nonfluorescent substances has been theoretically derived. An experiment has been performed with drinking water polluted by aromatic substances. The fluorescence ratio between CF and MPSF obtained has yielded the total absorption. Thus, it has been influenced by both fluorescent and nonfluorescent substances. In comparison to the conventional absorption technique, CF/MPSF has been characterized by high correlations to substance concentrations and has shown a much higher sensitivity. The method of CF/MPSF combines the advantage of fluorescence being very sensitive and of absorption spectrometry measuring the total absorption coefficient.

Using the method of multipath-saturation fluorescence, which considers both fluorescent as well as nonfluorescent substances, the total absorption coefficient can be determined with high sensitivity. This new fluorescence method is appropriate, e.g. for in-situ applications. Thus a portable absorption-fluorometer has been constructed. The main part of the device is a multireflection cell based on a design of Herriott with a 1 cm quartz-cuvette. Two pairs of spherical dielectric mirrors are used to realize the multireflection of the excitation radiation in the UV and blue spectral range. The combination of a cylindrical and a convace mirror leads to a long pathway of the excitation radiation and, thus, to a full absorption by the fluid. A first experiment has been performed with drinking water samples defined polluted by non-fluorescent p-nitrophenol and 2-nitroaniline. Based on the method of multipath-saturation fluorescence a good correlation to the substance concentration was achieved, whereas the conventional absorption failed.