Polyacrylamide gel electrophoresis of soil humic acid fractionated by size-exclusion chromatography and ultrafiltration

Abstract

A humic acid (HA) from chernozem soil has been fractionated either by size-exclusion chromatography (SEC) on Sephadex G-75 using water, Tris-HCl or 7 M urea as eluents, or by ultrafiltration (UF) in the presence of 7 M urea or water. UF-fractionated HA was classified as 100K (nominal retention size >100 000); 30K (100 000-30 000); 10K (30 000-10 000); 5K (10 000-5000). Several pools from each chromatography and all ultrafiltration retentates were assayed by polyacrylamide gel electrophoresis (PAGE). The results indicate that SEC fractionation gave a better separation of HA on fractions differing in electrophoretic mobility and molecular size (MS), and that apparently SEC is a more feasible technique than UF for soil HA fractionation; nevertheless the UF in 7 M urea solution might be useful for MS evaluation of HA fractions obtained by association SEC-PAGE. PAGE in the presence of denaturing agents can be successfully used for checking the purity of HA fractions obtained by both SEC and UF.