Fractionation by molecular weight of organic substances in Georgia coastal

• Main Author: John R. Wheeler
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1976
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.596.9819; http://www.aslo.org/lo/toc/vol_21/issue_6/0846.pdf

Ultrafiltration membranes were used to separate organic substances in Georgia coastal water into fractions to which approximate molecular weight (MW) ranges could be as-signed. Salt marsh water contained high concentrations of dissolved organic carbon between 1,000 and 30,000 MW, as well as high concentrations of dissolved carbohydrate in all MW classes. Concentrations of dissolved carbohydrate in offshore waters were low, and in some MW fractions ( especially those>30,009 MW) carbohydrate was at times undetectable. Absorbances at 254 mn by MW fractions roughly paralleled concentrations of dissolved organic carbon. Most of the color of marsh, sound, nearshore, and offshore waters, once the particles were removed, was due to substances between 1,000 and 30,000 MW. All organic material in seawater that passes through a filter with a 0.8-p or 0.45-p pore size has commonly been con-sidered dissolved. Recently attempts have been made to fractionate what should be termed filter-passing (rather than dis-solved) organic substances. Ogura ( 1970) showed that some organic material in the East China Sea that passed a 0.45, ~ pore-size filter was retained by a 0.1-p pore-size filter, indicating the existence of particles <0.45 p in diameter. He also suggested that some organic substances that pass a 0.45-p pore-size filter may be colloidal rather than dissolved. Sharp (1973) used a 0.025-p pore-size filter and an ultrafiltra-tion membrane with a cutoff of 50,000 mo-lecular weight (a nominal pore size of about 0.003,x) to fractionate organic sub-stances in the western North Atlantic Ocean; he found that the 0.025-0.8-p size fraction and the 0.003-0.025 ~ fraction each contained about 8 % of the total organic material, and that about SO % of the total passed the ultrafiltration membrane. Ogura ( 1974) used ultrafiltration membranes to fractionate by molecular weight ( MW) dissolved organic carbon (DOC) at two stations in Tokyo Bay. There was a ten-dency for the [DOC] in the>lOO,OOO-MW