Capillary electrophoresis for the characterization of humic substances

The potential of high performance capillary electrophoresis (HPCE), especially in the free solution mode (FSCE), is demonstrated for the analysis/characterization of environmental humic substances (HUS). The very high efficiency of HPCE separations allows the production of electropherograms that are more characteristic for HUS than are liquid chromatograms; in addition, HUS can be analyzed by FSCE in their naturally occurring anionic forms. Fulvic and humic acid fractions of HUS extracted from soil and water by procedures of the International Humic Substances Society were analyzed using an uncoated silica column and acetate, borate or phosphate buffer systems to produce electropherograms of the anionic species. Soil fulvic acids exhibit a consistent and characteristic set of sharp peaks, extending from a humic “hump”; migration times range between 5 and 12 min depending on soil source, buffer and pH. Humic acids give only the “hump,” which sometimes has shoulders but little definition. Soil and river humic acids produce only slightly different electropherograms at pH 8.30 in a borate buffer system, and each shows a remarkable peak-sharpening as the pH is increased to just 8.55. The electropherograms of “young” and “old” groundwater fulvic acids show different fingerprints.