Comparative study for the separation of aquatic humic substances by electrophoresis

Various humic and fulvic acids, isolated from natural waters, were investigated by the following electrophoretic techniques: free solution capillary electrophoresis (FSCE), capillary gel electrophoresis (CGE), isoelectric focusing (IEF) in ultra-thin layers, micellar electrokinetic chromatography (MEKC) acid SDS gradient-gel electrophoresis. A broad band is dominant in FSCE. The addition of 5 M urea to the running buffer facilitates the separation of the complex humic molecular aggregates, resulting in an increase in the number of peaks in the electropherogram. Under comparable denaturing conditions, and with a gel optimised for sieving single stranded deoxyoligonucleotides, CGE gives a separation with lower resolution than for DNA. Best separation is achieved by IEF in ultra-thin layers of polyacrylamide, giving about 20 sharp bands, SDS gradient-gel electrophoresis gave three similar bands for different fulvic acid samples, corresponding to molecular masses of standards of 1000, 6000 and 8000 g/mol. (C) 1997 Elsevier Science B.V.