Comparative study for separation of aquatic humic substances by capillary zone electrophoresis using uncoated, polymer coated and gel-filled capillaries

Several comparative capillary zone electrophoresis (CZE) experiments were carried out by means of uncoated, polyvinyl alcohol (PVA) and polyacrylamide (PAA) coated silica open tubular capillaries and gel-filled capillaries (linear non-cross-linked polyacrylamide, PAGE, by a pre-coated PAA capillary) using different kinds of background electrolytes (BGEs) and organic modifiers for characterization of aquatic dissolved humic matter (DHM). Organic compounds, such as acetic acid, acetate buffer, methanol, ethylene glycol, acetonitrile, dimethylsulphoxide, 5 M urea and sodium dodecyl sulphate (SDS) were tested as sample modifiers to improve the separative power. The fractionation mode by a PVA coated open tubular capillary using 40 mM phosphate buffer at pH 6.8 and 5 M urea–water as the sample modifier turned out to be fairly practical as well as its PAA homologue. Linear non-cross-linked PAGE with 10% gel concentration and 5 M urea–water as the sample modifier using 40 mM phosphate buffer at pH 6.8 produced the most reliable results as to the adaptation of physical gels, especially if the interactions of humic solutes with the gel matrix are not critical. The addition of SDS in the linear PAGE gel increased the interaction of humic solutes with the gel matrix but also improved the separative power and strengthened the chaotropic effect of the urea modifier.