Characterization of organic nitrogen in natural waters: Its molecular size, protein content, and interactions with heavy metals

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Abstract
The nitrogenous organic matter from two freshwater lakes and from the filtrate of a unialgal culture of Anabaena sp. was characterized chemically and evaluated for metal complexation ability. Proteinaceous matter was isolated from acidified samples by cellulose cation exchange columns and eluted with a basic salt solution. Isolated proteinaceous matter accounted for 14–34% of the original dissolved organic nitrogen. Gel permeation chromatography and ultrafiltration methods used to separate dissolved organic nitrogen into various size fractions yielded differing results, but most of the organic nitrogen had apparent molecular weights between 10,000 and 50,000 daltons. The copper‐complexing capacity of the proteinaceous matter was determined by differential pulse anodic stripping voltammetry. Conditional stability constants, which represent the mixed stability of all nonlabile ligands in the sample, ranged from 1.6 × 106 to 1.3 × 107 for the three samples.