Analysis of Metal‐EDTA Complexes by Electrospray Mass Spectrometry

Abstract

Solutions of the strong complexing agent ethylenediaminetetraacetic acid (EDTA) and Cu, Pb, Cd, AI, and Fe(III) were examined electrospray mass spectrometry (ES/MS). Uncomplexed EDTA and metaI-EDTA complexes survive the electrospray process intact and can be detected simultaneously by mass spectrometry. Best sensitivity was achieved in the positive ion mode in which EDTA and EDTAmetal complexes (present in solution as anions) were detected protonated species with a single positive charge. Except for the protonation, the aqueous metaI-EDTA complexes are preserved and neither fragmentation of complexes nor formation of clusters with more than one metal or iigand were observed in the mass spectra. Detection limits are between approximately 1 to 2 p~M for uncomplexed EDTA and for the Cu-EDTA and Pb-EDTA complexes, with a linear range up to 10 4 M. Calibrations based on solutions with eqnimolar concentrations of EDTA and Cu or Pb can be used to quantify EDTAmetal complexes in solutions with excess EDTA or metal, and in solutions with more than one metal present. Isotopic signatures of metals in the metal-ligand complexes are preserved, allowing the identification of the metal in a metaMigand complex. Isotopic signatures of metals can therefore aid in the identification of metaMigand complexes in unknown samples.

Electrospray Ionization Mass Spectrometry for the Quantification of Inorganic Cations and Anions

“…From comparisons of the LODs, sensitivities, formation constants of complexes (data not presented in this review), and from a consideration of the advantages in separation by size-exclusion chromatography, as outlined in the next section (i.e., the ligand with highest molecular weight was preferred), CyDTA was selected as being the best chelating agent for our purposes. These LODs are one to two orders smaller than those reported earlier for the detection of metal-EDTA complexes using ESI-MS, [16][17][18] or are comparable to those obtained in positive ion mode using cationic ion-pairing reagents with a metal-APC complex 19 . These values are almost the same, or slightly lower than, those for direct elemental measurement by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and atomic absorption spectrometry (AAS), although they are still three orders of magnitude larger than those of ICP-MS.…”

Electrospray mass spectrometry (ESI‐MS) in the study of metal–ligand solution equilibria

“…Refer to the cited studies (e.g., Combariza & Vachet (2003)) for a complete discussion. Other less common applications were the kinetic study of the complexation reaction (Boukhalfa & Crumbliss, 2000;Combariza & Vachet, 2002), and the determination of the concentration of metal ions in solution through complexation with a suitable ligand (or, vice versa, the determination of the concentration of a ligand through complexation with a suitable metal ion) (Baron & Hering, 1998;Satterfield & Brodbelt, 2000) (see also above, the auxiliary ligand strategy).…”

Characterization of aluminum species with nitrate, perchlorate and sulfate ions in the positive and negative ion mode by electrospray ionization mass spectrometry

“…In this study, a system containing aluminum and several anions other than Cl − in solution is examined. Studies of solutions containing Al 3+ and chelating agents [11] (anions), such as ethylenediaminetetraacetic acid (EDTA), [12,13] by ESI-MS have been reported and some of them indicate the applicability of ESI-MS to the study of aluminum-ligand solution equilibria. [14,15] However, the coordination of such ligands with Al 3+ is too strong to allow the discussion of the possibility of chemical modification such as fragmentation in a mass spectrometer (i.e.…”