Characterizing Interactions between Suwannee River Dissolved Organic Matter and Cu(II) Using Fluorescence Excitation−Emission Matrices and Parallel Factor Analysis

Mingquan Yan, Xiaona Ma, Jixia Cheng

 

 

ABSTRACT

 

This study investigated the binding of Cu(II) to dissolved organic matter (DOM) using the method of fluorescence excitation−emission matrix (EEM) combined with parallel factor analysis (PARAFAC). The examined DOM samples included Suwannee River natural organic matter (SRNOM), humic acid (SRHA), fulvic acid (SRFA) and hydrophilic acid (SRHPiA). The differences in metal binding properties were discerned via the behavior of individual groups of DOM fluorophores. PARAFAC examination showed that there were up to seven independent EEM components that behave differently in terms of the effects of Cu(II) on their fluorescence intensity. Component 1 (λexem = (270, 340, 395) nm /~500 nm) and Component 2 (λexem = (~240, 330) nm /~450 nm) were found to be responsive to Cu(II) binding in all four DOM samples. Component 3 (λexem = (220, 270-310) nm/400 nm) was present in the case of Cu(II) binding to SRNOM, SRFA, and SRHPiA. Component 4 (λexem = (260, 340) nm /470 nm), Component 5 (λexem = (220, 245, 280) nm /420 nm), and Component 6 (λexem = (220, 260, 340) nm /420 nm) were found in Cu(II) binding to SRNOM and SRHA, while Component 7 (λexem = (220, 260-340) nm/430 nm) emerged as a result of in Cu(II) binding to SRFA and SRHPiA. The apparent equilibrium constants of Cu(II) binding to each PARAFAC-discerned component were determined using the Ryan and Weber equation, and the corresponding log K values were in the range of 4.9-6.1 while the percentage of fluorescence intensity (f)that was quenched by Cu(II) was in the range of 0.45-0.99 for different DOM components discerned by PARAFAC. The results demonstrate that PARAFAC analysis of metals affecting on DOM EEM is a promising approach to gain better insight into the interactions between trace metals and specific groups of DOM fluorophores.

 

Keywords: EEM; PARAFAC; copper; complexation; dissolved organic matter

 

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doi:10.11912/jws.3.3.165-177