Advances in mass spectrometry for iron speciation in plants

Iron is an important nutrient essential for plants and critical for human health. The state-of-the art of methods for iron speciation in cereal grains and plant fluids is critically reviewed. Particular attention is given to the latest developments in the coupling of HPLC with the parallel ICP MS and electrospray ionization (ESI) MS/MS detection, usually QTOF MS or Q-Orbitrap MS, for the identification and quantification of iron species. The coupled techniques allow the direct microanalysis of plant intracellular fluids (xylem and phloem) and complement X-ray absorption spectroscopy (XANES and EXAFS). The increasing resolution and sensitivity of electrospray mass spectrometers and emergence of software allowing extraction of iron specific data from large chromatographic data sets are responsible for the growing role of electrospray MS/MS in speciation studies. The use of stable isotopes for the probing of the reactivity and stability of endogenous metal complexes and quantitative analysis are rising in importance.