The relative importance of molecular size and charge differences in capillary electrophoresis of humic substances of different origin

摘要

In conventional polyacrylamide gel electrophoresis (PAGE), molecular size differences can explain more than 95% of variations in the electrophoretic mobility of fractions of humic substances of reduced molecular weight polydispersity extracted from the same soil. Capillary electrophoresis (CE) is, however, entirely peculiar in that specific factors such as the electro-osmotic flow (EOF) can affect not only the efficiency but even the mechanism of the separation itself. In particular, humic substances (HSs) that would naturally migrate towards the anode under the influence of the electric field are instead driven to the cathode by the EOF generated by the migration of cations near the negatively charged surface of the capillary. However, the main factor influencing the capillary electrophoretic behaviour of HSs, even under conditions where the normal migration direction is reversed, is still the molecular size. The enormous separation efficiency of CE might allow the detection of significant charge effects when comparing the mobilities of corresponding fractions of reduced molecular size polydispersity of HSs extracted from different peats and soils.