Properties of the Yellow Organic Acids of Natural Waters1

Gel filtration profiles obtained from a variety of naturally colored waters indicate that color producing molecules are mostly in the apparent molecular weight range of 700–10,000 relative to dextrans. One fraction seems to have a molecular weight in excess of 50,000. The apparent size of the color molecules was found to be pH dependent, increasing as pH increases. Size increases are attributed to increased functional group ionization and a decrease in the adsorbability on Sephadex. The degree of association of color molecules with iron was also found to be pH dependent, being greater at both high and low pH than in the range of 7–8.