Proposed guidelines for sample preparation and ESI-MS analysis of humic substances to avoid self-esterification

摘要

Standard humic substances (HS) were stored in C-13-labelled methanol, ethanol, 2-propanol and d(3)-methanol to investigate whether they underwent self-esterification with the solvents or not. Data from stable carbon isotope analysis: C-13 NMR spectroscopy and electrospray ionisation mass spectrometry (ESI-MS) showed that significant self-esterification of carboxyl groups began immediately after dissolution. The major implication is that data collected in previous studies using these solvents in conjunction with HS are likely to be compromised. Self-esterification was minimised by varying parameters such as % water, temperature, concentration, storage time and buffer. Solvent reactivity was found to be: ethanol > 2-propanol > methanol. The study proposes preliminary guidelines for the preparation and storaqe of HS and their analysis by ESI-MS. The primary recommendation is to avoid the use of these solvents and use alternatives such as acetonitrile and water. (c) 2004 Elsevier Ltd. All rights reserved.