Electrospray ionisation-mass spectrometry of hydroxamate siderophores

Electrospray ionisation-mass spectrometry (ESI-MS) was applied to the detection of the iron complexes of the hydroxamate type siderophores ferrioxamine (FO), ferrichrome (FC) and iron(III) rhodotoluate (FR). Mass spectra of the three siderophores produced by ESI-MS were dominated by the protonated (M + 1)+ parent ions, except for FR at pH 4.3, which was present as the positively charged 1:1 complex. On collision with He ions, fragmentation proceeded largely via cleavage of C-N bonds. Flow injection analysis of the siderophores with detection by ESI-MS produced detection limits of 1.9 fmol for FO, 31.1 fmol for FC and 524 fmol for FR.