Fast Atom Bombardment Mass Spectrometry of EDTA Complexes

Abstract

The mass spectra of EDTA salts and complexes were measured by means of FABMS. Three main quasi-molecular ions, (M-A+H+H)⁺, (M+H)⁺, and (M+A)⁺ were detected, in which M and A represent EDTA molecule and alkali metal element, respectively. In the case of EDTA containing only alkali metal element, six characteristic ions {(H_5-n AnY)⁺ n=0 to 5, and Y represents (^-OOCCH₂)₂ NCH₂CH₂N (CH₂COO^-)₂} were observed. Comparing the intensities of three characteristic ions of EDTA containing alkali earth metal elements (Mg, Ca, and Sr) with (2G+H)⁺ ion of glycerin, we found that the intensities of characteristic ions were in proportion to the order of the inverse of the ionic radii of the elements. However, in the cases of the EDTA complexes containing transition metal elements, the order of the intensities of characteristic ions are turned out to be as follows,
Mn²⁺ > Co²⁺ > Ni²⁺ > Cu²⁺ < Zn²⁺.
In the case of EDTA containing Fe(III), both oxidation and reduction reactions were recognized. Moreover, in the case of non-metal EDTA compound, both (M+H)⁺ and (M+NH₄)⁺ quasi-molecular ion were detected. In a few EDTA complexes, dimer quasi-molecular ions were also detected.