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Abstract
Dissolved organic matter and water-extractable organic matter influence soil biological activity, affect the transport of metals and organic pollutants, and contribute to mineral weathering and podzolisation. An important part of soil organic matter (SOM) are humic substances (HS), the major sinks of organic carbon on Earth, found everywhere including Antarctica. HS and humic acids are isolated from soils using various extraction agents and isolated products are often characterised by mass spectrometry. In this work, detailed study of laser desorption ionisation of SOM and of humic acids directly from soils was performed. The micro-extraction procedure was optimised and the most suitable method was found to be direct ionisation of SOM from a soil after addition of a diluted NaOH solution. In this way, in situ release of adsorbed and bound SOM from soils is achieved and direct analysis by laser desorption ionisation time-of-flight mass spectrometry is possible without any tedious extraction procedure. The developed methodology enables fast screening of soil organic matter to obtain fingerprints and thus to follow the differences between soils from various environments. The developed procedure was applied to soil samples from several continents, including Antarctica, and to volcanic soils from the Canary Islands.
Acknowledgements
Support from Ministry of Education, Youth and Sports of the Czech Republic (Projects MSM 0021622411 and LC 06035) and Academy of Sciences of the Czech Republic (Project KAN 101630651) are greatly acknowledged. E.M. Peña-Méndez thanks to the Dirección General de Universidades of the Canarian Government (Spain) for the financial support. English usage was kindly revised by Mr Philip G. Watson.