Characterization of humic and soil particles by analytical pyrolysis and computer modeling

The methodology for analytical pyrolysis of humic acids (HA), fulvic acids (FA), dissolved organic matter (DOM), and humic as well as soil particles, is reviewed. This includes recent developments in off-line pyrolysis, direct pyrolysis-mass spectrometry (Py-MS), and Curie-point pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in combination with library searches. In addition, investigations of extracted soil organic matter (SOM), organic-mineral fractions and whole soils are reported. Preliminary results of structural modeling and geometry optimization of HA, SOM, and soil particles are introduced. Molecular mechanics calculations to evaluate the conformation of structural, three-dimensional models and to determine first quantitative structure-activity relationship (QSAR) properties are put forward. QSAR investigations allow the correlation of molecular structures with soil properties such as mass, surface area, volume, partial charges (electronegativity), polarizability, refractivity, hydrophobicity, and hydration energy. The principal aim and long-term strategy are to develop structural concepts of SOM and soil particles which explain their composition as well as their ecological meaning, dynamic character and structure-property relationships in whole soils. Focal points in the applications of analytical pyrolysis in soil science are, first, the dynamics of soil organic matter such as formation, turnover, seasonal variations, and influence of soil managements and second, ecological consequences such as characterization of contaminated soils (sewage farms, bound residues).