Characterisation of Fulvic Acids and Glycyrrhizic Acid by Time-of-Flight Secondary Ion Mass Spectrometry

Abstract

Fulvic acids of different origin, spray deposited on polished silicon after dissolution in high‐purity water without any additives, were analysed by time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) in combination with oblique 24...36 keV SF5+ ion bombardment. The observed, highly reproducible mass spectra cover more than five orders of magnitude in dynamic range, without background subtraction. Apart from lines due to atomic ions and low‐mass ion fragments, the mass spectra exhibit broad maxima between m/z 200...350, mainly due to a beat‐like superposition of lines at every single mass number, up to at least m/z 400. In the negative ion spectra the beats have a spacing of m/z 14, corresponding to a CH2‐unit. The high‐mass tails of the spectra extend well beyond m/z 5000, with similar slopes in the positive and the negative ion mass spectra. The negative spectra appear to be less affected by fragmentation products than the positive spectra. Fulvic acids (FAs) of different origin show distinctly different spectra, with mean masses ranging between m/z ≈ 450 and 580 (for a low‐mass cut‐off m/z 150). To further verify the ability of TOF‐SIMS to detect molecules and clusters with masses significantly above the maxima of the FA spectra, samples of glycyrrhizic acid (GA, as GA ammonium salt with molecular weight 840) were also analysed. Parent ions as well as multimers (GA)n were observed as positive and negative ions, up to n = 4 (m/z 3320). The results are compared with spectra recently obtained by other mass spectrometric techniques.

Hydrophilic olive cake extracts: Characterization by physicochemical properties and Cu(II) complexation

“…Solid samples for TOF-SIMS analysis were prepared by spray-deposition on cleaned silicon substrates with a hydrophilic character [20]. Solutions of 30 mg/L of extract were dissolved in a dilute aqueous solution of NH4OH and typically 400 L of solution were sprayed.…”

Combustion characteristics of water-insoluble elemental and organic carbon in size selected ambient aerosol particles

“…Thorough electrospray mass spectrometric analyses of a variety of fulvic acids, the water soluble components of humic acids, revealed broad spectra extending from about m/z 100 to m/z 500 and beyond (Plancque et al, 2001). Similarly, time-of-flight secondary ion mass spectra of solidified fulvic acids were found to exhibit tails up to at least m/z 3000 (Szymczak et al, 2000). The proposed structure of fulvic acid molecules features a benezene ring substituted with carboxyl groups and alkyl chains (Plancque et al, 2001).…”

Self‐esterification of fulvic acid model compounds in methanolic solvents as observed by electrospray ionization mass spectrometry

“…They are ubiquitous in aquatic and terrestrial environments and play an important role in the fate and transport of nutrients and contaminants. Electrospray ionization mass spectrometry (ESI‐MS) and other soft ionization mass spectrometric techniques have been found to be particularly suited to the mass analysis of humic substances 1–13. They have provided highly detailed mass data that permit study at a molecular level.…”