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|Title:||Metal Speciation Determined Using Multiresponse Fluorescence|
|Abstract:||<p>metal fate, transport and toxicity are speciation dependent. Natural organic matter (NOM) is a complex mixture of many potential metal binding sites and it is ubiquitous in the environment. Therefore, a site-specific, non-invasive, sensitive method is required to investigate metal interactions with NOM. This thesis considers the development and application of a multiresponse fluorescence method to determine site-specific binding of Al, Cu and H to model NOM ligands, fulvic acid and isolated NOM samples. Natural organic matter is treaed as a mixture of average binding sites. The minimum number of sites along with their excitation and emission wavelengths are determined from deconvolution of fluorescence surfaces using SIMPLISMA (Windig and Guilment, Anal. Chem. 1991, 63, 1425-1432). Fluorescence at wavelengths corresponding to these components is measured during metal titration and the multiresponse data are fit to a multi-site speciation model for the metal-NOM system. This multiresponse fluorescence method is validated in that it recovers known values for Al with two model ligands simultaneously and predicts free copper during a titration of Suwannee River fulvic acid within 0.1 log units when compared to the model of Cabaniss and Schuman (Geochim. Cosmochim. Acta 1988, 52, 185-193). A total of seven different fluorophores were identified in NOM isolated from nine different watersheds in Norway. Each sample contained four to six of the seven identified fluorophores. On average, at pH 4, the fluorophores bind Al with a strength similar to salicylic acid (logK'≈5.5), although there are stronger and weaker sites with logK'≈7 and logK'≈3, respectively. The speciation results are dependent on the isolation method used to obtain the NOM sample. For the NOM samples, the difference between reverse osmosis and low-pressure-low-temperature evaporative isolates are as large as the differences between sampling sites. Suwannee River fulvic acid is represented by five fluorescent binding sites for Cu, Al and H binding. The constants for Al and Cu are consistent with salicylic acid-like sites and the H binding can only be explained if diprotic sites are used. Thus, multiresponse fluorescence methods allow discrimination between monoprotic and polyprotic models. Finally, a protocol is proposed for multiresponse fluorescence determination of metal interactions with NOM.</p>|
|Appears in Collections:||Open Access Dissertations and Theses|
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