Multi-site aluminum speciation with natural organic matter using multiresponse fluorescence data

A revised method for determining conditional binding constants and site concentrations for Al and natural organic matter (NOM) is presented. By using total luminescence spectroscopy and multiresponse parameter estimation, the method is capable of resolving Al complexation at discrete sites within NOM. The method is tested on a mixed model ligand system of salicylic acid and 2-hydroxy-3-napthoic acid and recovers known values for stability constants and ligand concentrations. The method is also applied to a sample of filtered river water at pH 4.02 and reveals three sites with conditional stability constants with log values of 5.77, 5.56 and 5.81 and standard deviation of 0.09. In addition, for the same three sites the densities are determined to be 0.427, 0.448 and 0.354 μmol mg−1 of dissolved organic carbon (DOC), with a standard deviation of 0.14 μmol mg−1 of DOC.