ASFit - An all-inclusive tool for analysis of UV–Vis spectra of colored dissolved organic matter (CDOM)

The study of dissolved organic matter (DOM) in natural waters is hindered by its complex structure and low concentration. Spectroscopic methods (e.g. UV–Vis spectrometry) can be used for the characterization of its chromophoric fraction (CDOM) due to their simplicity, rapid response, low price and high sensitivity. The absorption spectrum of CDOM is unstructured with an exponential decrease in absorbance at increasing wavelength. Absorbance intensity gives an indirect estimate of CDOM concentration, whereas the shape of the spectrum provides insights into its composition. Changes in absorbance spectra can therefore be useful indicators of sources, degree of degradation as well as interactions of DOM with metals. There are over 20 different parameters that can be derived from the UV–Vis spectra in order to gain information on CDOM in natural waters. Only few of these parameters are commonly used (e.g. S275-290, S350-400, SR, SUVA, a254), the others are proposed based on "well correlated" relationship with other DOM specific parameters. Analysis and interpretation of UV–Vis spectra are challenging since there are numerous possibilities to treat the raw spectra and there is still no general agreement among scientists on the interpretation of all these parameters. Here we present ASFit, a new, windows-based "all-inclusive" software tool, for the basic and advanced treatment of CDOM UV/Vis spectra. It computes the most used parameters in few seconds and presents data in interactive graphs. ASFit can also be used to study trace metals complexation with DOM based on differential spectra.