Abstract
For the purpose of clarifying the properties of fulvic acid, considered to contribute much to trihalomethane production, the method of determining molecular weight by using gel chromatography or ultra-filtration, for the case of samples coexisting with salts, was studied. And, the molecular weights of the fulvic acids separated from 4 humic acid reagents and Tone River water were compared.
The gel chromatograms of desalted fulvic acid samples showed a broad peak. Second peak appeared when NaCl was added into the samples. The Kd value of the second peak rose and reached the value of 1.0, with increasing NaCl concentration in the samples. The reason of this rise of Kd value was considered to be the “promotion of adsorption or dispersion”, instead of the “negation of ion exclusion effect” by NaCl. The solute separation by ultrafiltration was found to be smaller for the samples with higher NaCl concentration, and larger for the samples with higher pH.
So, for the determination of the molecular weight of fulvic acid by using gel chromatography or ultrafiltration, it is necessary to measure by desalting the samples, or extrapolating the salt concentration to zero.
