Method Considerations for Compound Identification in Complex Mixtures Using Electrospray Ionization Ultrahigh Resolution Mass Spectrometry

Comparison of Sample Preparation Techniques for the (−)ESI-FT-ICR-MS Analysis of Humic and Fulvic Acids

“…HA fractions have been previously dissolved in neutral MeOH:water mixtures, , basified MeOH:water mixtures with NaOH, basified MeOH:water mixtures with NH 4 OH, − , acidified MeOH:water mixtures with acetic acid, basified MeOH:water mixtures with NaOH followed by cation-exchange, neutral MeOH, basified water with NH 4 OH, ,− as well as in basified water with NaOH followed by cation-exchange and solvent extraction of the resin . Commonly, NH 4 OH is added after HA had been already solubilized, and thus, NH 4 OH only serves as an ionization enhancer. − ,, The addition of NH 4 OH is necessary as HA fractions are often rich in poorly ionizable aromatic and condensed aromatic molecules. , In other studies, however, NH 4 OH was simultaneously added when the powdered HA was mixed with the solubilization solution, and thus, NH 4 OH served both as a basification agent and an ionization enhancer. ,,− Recent work, however, has shown that the use of NH 4 OH can induce nitrogen-incorporation and possibly bias the mass spectrometric analytical window, but this has not been assessed for HA matrices.…”