Complexation of metals by phytosiderophores revealed by CE-ESI-MS and CE-ICP-MS

CE-ESI-MS and CE-ICP-MS were implemented for studying three phytosiderophores (mugineic acid, epi-mugineic acid and deoxymugineic acid) and their metal complexes. Free ligands and ferric complexes were analyzed using the first methodology, while six free metals (Co(II), Cu(II), Fe(III), Mn(II), Ni(II) and Zn(II)) together with the corresponding complexes were investigated by the latter technique. CE separation was realized at a voltage of +25 kV employing a BGE containing 20 mM ammonium bicarbonate at pH 7.2. Both techniques revealed limits of detection in the high nM to low M range. Standard additions to hydroponic samples of H. distichon, cv. Bodega (spring barley) showed regression coefficients for the metal-ligand complexes ranging from 0.984 to 0.999. Additionally, results of a competitivity study allowed the determination of relative metal-phytosiderophore complex stability constants of deoxymugineic/mugineic acid.