Monitoring natural organic matter in water with scanning spectrophotometer

This study uses scanning ultraviolet-visible (UV-Vis) spectrophotometer to monitor natural organic matter (NOM) in water. The results showed that the area under the UV-Vis spectra is a good surrogate to monitor the concentration of the aqueous NOM. No apparent difference was found between the spectra of the three commercially available humic acids used in this study. The use of the scanning spectra compensates the potential random error in the absorbance determined at single wavelength due to the heterogeneous NOM compositions. The major interference of the proposed method comes from the formazine turbidity and nitrate nitrogen (NO₃^--N). Although filtration with a 0.45-υm filter can remove most of the interference from formazine, some interference is still present at a wavelength less than 250 nm. Also it is found that the presence of the NO₃^--N greatly affect the spectra of the NOM. In order to monitor the NOM in water with minimized interference, it is recommended that the area under the spectra between 250 and 350 nm should be used as a surrogate for concentration of NOM in water.