Fingerprinting Metal-Containing Biomolecules after Reductive Displacement of Iron by Gallium and Subsequent Column-Switched LC−ICPMS Analysis Applied on Siderophores

Column-switching liquid chromatography followed by low-resolution ICPMS was evaluated as a tool for speciation analysis of metal-containing biomolecules. The strategy was applied on siderophores, strong iron chelators of low molecular weight (M w < 1500). Prior to the LC−ICPMS analysis, reductive displacement of iron by gallium was performed using ascorbate as the reducing agent to increase the sensitivity. Different experimental conditions during the exchange reaction were tested using ferrichrysin and ferrichrome for evaluation. A reaction time of 30 min and a pH of 3.9 gave an exchange yield of 27 and 83% for ferrichrysin and ferrichrome, respectively. A gradient elution profile was also developed to separate gallium-chelated siderophores on a PGC column. Detection limits for standard solutions of ferrichrysin and ferrichrome in the low-nanomolar range were obtained by monitoring the gallium-69 isotope. The combined use of LC−ICPMS and LC−ESI-MS/MS was also evaluated as a tool to identify unknown metal complexes, here siderophores, in field soil solution samples.