APPLICABILITY AND RELIABILITY OF GEL-FILTRATION TO STUDY AQUATIC HUMIC SUBSTANCES REVISITED - THE EFFECTS OF PH ON MOLECULAR-SIZE DISTRIBUTIONS

The effect of pH on the molecular size distribution of dissolved humic substances (DHS) in surface waters from four different lakes in north ern Europe was studied using Sephadex G-100 gel filtration chromatogra phy (GFC). New methods for the analysis of the elution profiles obtain ed are introduced, employing parallel graphical and statistical approa ches. For all samples investigated, the proportion of the DHS eluted i n the excluded fraction tended to diminish with decreasing pH. At the same time, the remaining DHS eluted tended to decrease in apparent mol ecular size with decreasing pH. Analyses of the elution profiles revea led that the apparent conformational flexibility of the DHS in the sam ples was greatest for the samples of lowest ionic strength. The applic ability and reliability of GFC as a tool for the investigation of aqua tic humic substances are discussed.