Photoinductive properties of soil humic acids and their fractions obtainedby tandem size exclusion chromatography-polyacrylamide gel electrophoresis

Humic acids (HAs) from three soils of different origin (Chernozem, Ferralso l and Ranker) have been fractionated by coupling size exclusion chromatogra phy (SEC) and polyacrylamide gel electrophoresis (PAGE) on three fractions (fractions A, B, C + D) with different molecular sizes (MSs) and exactly de fined electrophoretic mobility (EM). Fractions identically marked had simil ar EM and MS, independently of HA sources. The photoinductive properties of the whole HAs and their fractions were compared by studying the photoinduc ed transformation of fenuron at 365 nm. High MS fractions A and B appeared to exhibit poor photoinductive activities compared to the whole HAs, wherea s low MS fraction C+D in Chernozem and Ranker were more efficient than the whole HAs. A fourth intermediary fraction containing a mixture of fractions B and C + D with small amount of D was shown to photoinduce poorly the tra nsformation of fenuron. It was therefore concluded that the molecules capab le of photoinducing the transformation of fenuron were mainly contained in fraction D. Fluorescence properties of Chernozem HA and its fractions have been tested. Fraction C + D exhibited a very similar fluorescence emission spectrum in comparison with the whole HA and in contrast, the fractions A a nd B emitted very weakly. (C) 2001 Elsevier Science Ltd. All rights reserve d.