Development of differential absorbance spectroscopy for the study of metal complexation behavior of natural organic matter

Corrosion processes in drinking water distribution systems can result in release of metals which have harmful human health effects and can also result in destruction of plumbing materials requiring costly replacement and repairs. The role of NOM in promoting corrosion is not fully understood, and analytical techniques capable of elucidating the mechanisms of NOM-metal interactions under realistic drinking water conditions are lacking.;This study examined the utility of differential absorbance spectroscopy to identify mechanisms of NOM interactions with metals commonly found in drinking water distribution systems. The protonation and metal-binding behavior of standard fulvic and humic acids was examined, and the differential spectra were compared to those generated for simple model organic compounds as well as for unfractionated NOM from the Potomac River. The differential spectra could distinguish between contributions of carboxylic and phenolic-type chromophores to the acid-base behavior of these compounds. The differential spectra could also reveal the difference between complexation and oxidation mechanisms of NOM interactions with metals. Differential spectra features could be correlated with other independent spectroscopic measurements as well as to well-attested metal complexation model predictions. This study suggests that differential absorbance spectroscopy is capable of providing information about these interactions at concentrations of NOM and metals which are realistic for drinking water systems without a need for time-consuming pre-concentration or separation processes.