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Fluorescent Dissolved Organic Matter in Natural Waters
In case of tryptophan-like substance or extracellular polymeric substances
(EPS), the fluorescence intensities at peak T- and peak T UV -regions are the highest at neutral pH (7.0) and often decrease when the solution pH increases (9.0)
or decreases (4.0) (Fig. 9) (Zhang et al. 2010). The EPS is mostly composed of
tryptophan-like substances that show a twice higher fluorescence intensity at peak
T UV than at peak T (Fig. 9). The pH effect on tryptophan-metal complexation has
some characteristic features. The fluorescence intensity of peak T UV is highest at
pH 6 and peak T is similar at pH 6–8, differently from the trend of tryptophan fluorescence (Fig. 9) (Zhang et al. 2010). The fluorescence intensities of tryptophan
Fluorescence intensity (a.u.)
pH
Peak T
Peak T UV
(a)
(b)
Fig. 9 Changes in the fluorescence intensities of peak T (a) and peak T UV (b) for extracellular
polymeric substances (EPS) with solution pH in the absence and presence of 3.0 mg L −1 Hg(II).
The error bar indicates the standard deviation of three independent measurements. Data source
Zhang et al. (2010)