INFLUENCE OF BORATE BUFFERS ON THE ELECTROPHORETIC BEHAVIOR OF HUMIC SUBSTANCES IN CAPILLARY-ZONE-ELECTROPHORESIS

The influence of tetrahydroxyborate ions on the electrophoretic mobili ty of humic acids was evaluated by capillary electrophoresis (CE). Dep ending on the molarity of berate ions in the separation buffer, the hu mic acids exhibit electropherograms with sharp peaks consistently exte nding from a ''humic hump''. The variations in the migration times of these peaks depend on the concentration of borate ions in the separati on buffer. The complexation of berate ions and humic acid fractions wa s also analyzed with B-11 and H-1 NMR spectroscopy as well as UV spect rophotometry in solutions of the same composition as the CE separation buffers. Supplementary studies with model compounds (flavonoids, phen olic and sugar acids) indicate reaction mechanisms that include the fo rmation of bidentate esters (monocomplexes) as well as spiranes (tetra dentate esters or dicomplexes) within the humic substructure. Special attention must be given to the interpretation of CE electropherograms while fingerprinting humic substances with berate buffers since observ ed peaks do not necessarily indicate distinct humic components but may be artifacts caused by the interaction of the berate ions with the hu mic substances.