POLYACRYLAMIDE-GEL ELECTROPHORESIS OF SOIL HUMIC-ACID FRACTIONATED BYSIZE-EXCLUSION CHROMATOGRAPHY AND ULTRAFILTRATION

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 presenc e of 7 M urea or water. UF-fractionated HA was classified as 100K (nom inal retention size >100 000); 30K (100 000-30 000); 10K (30 000-10 00 0); 5K (10 000-5000). Several pools from each chromatography and all u ltrafiltration retentates were assayed by polyacrylamide gel electroph oresis (PAGE). The results indicate that SEC fractionation gave a bett er separation of HA on fractions differing in electrophoretic mobility and molecular size (MS), and that apparently SEC is a more feasible t echnique than UF for soil HA fractionation; nevertheless the UF in 7 M urea solution might be useful for MS evaluation of HA fractions obtai ned by association SEC-PAGE. PAGE in the presence of denaturing agents can be successfully used for checking the purity of HA fractions obta ined by both SEC and UF.