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INFLUENCE OF BORATE BUFFERS ON THE ELECTROPHORETIC BEHAVIOR OF HUMIC SUBSTANCES IN CAPILLARY ZONE ELECTROPHORESIS
Citation:
Schmitt-Kopplin, P., N. Hertkorn, A. Garrison, D. Freitag, AND A. Kettrup. INFLUENCE OF BORATE BUFFERS ON THE ELECTROPHORETIC BEHAVIOR OF HUMIC SUBSTANCES IN CAPILLARY ZONE ELECTROPHORESIS. Analytical Chemistry 70(18):3798-3808, (1998).
Description:
The influence of tetrahydroxyborate ions on the electrophoretic mobility of humic acids was evaluated by capillary electrophoresis (CE). Depending on the molarity of borate ions in the separation buffer, the humic acids exhibit electropherograms with sharp peaks consistently extending from a "humic hump". The variations in the migration times of these peaks depend on the concentration of borate ions in the separation buffer. The complexation of borate ions and humic acid fractions was also analyzed with 11B and 1H NMR spectroscopy as well as UV spectrophotometry in solutions of the same composition as the CE separation buffers. Supplementary studies with model compounds (flavonoids, phenolic and sugar acids) indicate reaction mechanisms that include the formation of bidentate esters (monocomplexes) as well as spiranes (tetradentate esters or dicomplexes) within the humic substructure. Special attention must be given to the interpretation of CE electropherograms while fingerprinting humic substances with borate buffers since observed peaks do not necessarily indicate distinct humic components but may be artifacts caused by the interaction of the borate ions with the humic substances.