Molecular Weight Characterization of Humic Substances by MALDI-TOF-MS

Abstract

This study involved the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to determine the molecular weight distribution of the humic substances, humic acid (HA), and fulvic acid (FA), extracted from peat and soil. The results of MALDI-TOF-MS were compared with the conventional method of high performance size exclusion chromatography (HPSEC) for determining the molecular size distribution of the humic substances. The number-average molecular weight (Mn) of peat-based HA, peat-based FA, soil-based HA, and soil-based FA evaluated by MALDI-TOF-MS were 3,700, 2,900, 10,500, and 9,700, respectively. These results indicate that FA has a lower molecular weight than HA in samples of the same origin, and peat-based HA and FA have considerably lower molecular weights than soil-based HA and FA.