Electron paramagnetic resonance (EPR) studies on stable and transient radicals in humic acids from compost, soil, peat and brown coal

Quantitative EPR method was applied to characterise four types of humic aci ds (HA) derived from composts. soil, peat and soft brown coal. For each sam ple of HA the level of native (indigenous) radicals was estimated. Interact ions of the HA with various gaseous agents and organic solvents were invest igated. Strong effects of gaseous ammonia and aliphatic amines on spin conc entration enhancement were observed: additionally, higher values of g-value were found to be associated with the formed 'transient' radicals. Correlat ion of copper(II) ions uptake by different HA with effect diminishing prima ry spin concentration was established. It was recognised that the radical c entres, which are enhanced by 'ammonia effect' are quenched in the formed H A-Cu(II) complexes. The both opposite effects are competitive from each oth er, where 'copper(II) quenching effect' prevails. Reaction of nitrogen diox ide with the humic acids was also examined. The presence of diketones and;o r other compounds with active methylene group results in formation of the i minoxy radicals; these radicals are immobilized in the solid (macromolecula r) matrix of the humic acids. (C) 2000 Elsevier Science B.V. All rights res erved.