Capillary electrophoretic behaviour of humic substances in physical gels

We investigated the principles of the capillary electrophoretic behaviour o f humic substances (HSs) in physical gels. Long chain (M-r 4000, 6000 and 2 0 000) polyethylene glycols (PEGs) at concentrations above their entangleme nt threshold caused the separation of HS fractions according to molecular s ize differences. Close linear relationships between effective mobilities an d mean apparent molecular masses were observed at PEG concentrations betwee n 2.5 and 15%. The efficiency of the separation does not increase in gels o f increasing polymer concentrations. The possibility of interactions betwee n HSs and gel-forming polymers was also investigated. Short chain (M-r 400) PEGs, added to the buffer at concentrations from 2.5 to 12.5%, increased t he migration times of all HS fractions, but no separation was obtained even at large polymer concentrations, showing that gel formation was essential for the separation. In 2.5% polyvinyl alcohol (PVA) 49 000 all fractions sh ow two unresolved, but well defined peaks. This separation is probably arte factual and depends on the relative concentration of HSs and PVA, as the re lative abundance of the peaks changes with the sample concentration. (C) 19 99 Published by Elsevier Science B.V. All rights reserved.