Speciation of Fe(III)-chelate complexes by electrospray ionization ion trap and laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was employed as a relatively simple technique to investigate the speciation of complexes formed between Fe(III), the iron chelator 3-hydroxy-2-methyl-1-propyl-1H-pyridin-4-one (L) and citrate. The major species in aqueous solution at pH 6.0 of a 1:2:10 molar mixture Fe(III)/L/citrate is the Fe(III)L-2 complex. No evidence for a mixed citrate complex was observed. Furthermore, evidence for the existence of a number of dimeric iron species is presented. All observed species in ESI were singly charged as evidenced by the isotopic envelopes. Laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (LDI-FTICRMS) provided data that complemented and confirmed the ESI findings. We also demonstrate the possibility of chelated Fe(III) being converted to Fe(II) under ESI and LDI conditions. Copyright (C) 2002 John Wiley Sons, Ltd.