CHARACTERIZATION OF SOIL ORGANIC-MATTER USING ISOELECTRIC-FOCUSING - A COMPARISON OF 6 COMMERCIAL CARRIER AMPHOLYTES

The use of isoelectric focusing (IEF) to characterize soil humic subst ances is a technique that appears to be of widespread interest. The us e of carrier ampholytes permits the electrophoretic separation in the presence of a pH gradient, but until now the problem of interferences that could occur between the soil organic matter and the carrier ampho lytes during the IEF separations have not been recognized. The commerc ial carrier ampholytes have different chemical structures; thus, inter ferences with soil humic substances could be different. In this study, two soil extracts were fractionated using the IEF technique in the pr esence of six commercial carrier ampholytes with a wide pH range (abou t 310). The main results can be summarized as follows: (i) Each amphol yte used had a marked influence on the patterns obtained, and good res olution of the focused bands was obtained only in the presence of some carrier ampholytes (Ampholine and Preblended Ampholine from Pharmacia -LKB and Bio-Lyte from Bio-Rad). (ii) The carrier ampholytes influence d both the number and the apparent isoelectric point of the focused ba nds. The achievement of a pH gradient that allows electrophoretic runs without formation of complexes and of possible interferences between carrier ampholytes and humic substances is still to be shown. However, the IEF technique is highly reproducible and useful for the character ization of soil humic substances once the experimental conditions and the carrier ampholytes are precisely defined.