Identification of metal species by ESI-MS/MS through release of free metals from the corresponding metal-ligand complexes

Electrospray ionization-mass spectrometry (ESI-MS) is used to analyze metal species in a variety of samples. Here, we describe an application for identifying metal species by tandem mass spectrometry (ESI-MS/MS) with the release of free metals from the corresponding metal–ligand complexes. The MS/MS data were used to elucidate the possible fragmentation pathways of different metal–deoxymugineic acid (–DMA) and metal–nicotianamine (–NA) complexes and select the product ions with highest abundance that may be useful for quantitative multiple reaction monitoring. This method can be used for identifying different metal–ligand complexes, especially for metal species whose mass spectra peaks are clustered close together. Different metal–DMA/NA complexes were simultaneously identified under different physiological pH conditions with this method. We further demonstrated the application of the technique for different plant samples and with different MS instruments.