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Anal Bioanal Chem (2013) 405:54115419 DOI 10.1007/s00216-013-6959-1
RESEARCH PAPER
Iron (Fe) speciation in xylem sap by XANES at a high brilliant synchrotron X-ray source: opportunitiesand limitations
Roberto Terzano & Tanja Mimmo & Bart Vekemans &
Laszlo Vincze & Gerald Falkenberg & Nicola Tomasi &
Magali Schnell Ramos & Roberto Pinton & Stefano Cesco
Received: 4 March 2013 /Revised: 27 March 2013 /Accepted: 28 March 2013 /Published online: 24 April 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract The development of highly brilliant synchrotron facilities all around the world is opening the way to new research in biological sciences including speciation studies of trace elements in plants. In this paper, for the first time, iron (Fe) speciation in xylem sap has been assessed by X-ray absorption near-edge structure (XANES) spectroscopy at the highly brilliant synchrotron PETRA III, beamline P06. Both standard organic Fe-complexes and xylem sap samples of Fe-deficient tomato plants were analyzed. The high photon flux provided by this X-ray synchrotron source allows on one side to obtain good XANES spectra in a reasonable amount of time
(approx. 15 min for 200 eV scan) at low Fe concentrations (sub parts-per-million), while on the other hand may cause radiation damage to the sample, despite the sample being cooled by a stream of liquid nitrogen vapor. Standard Fe-complexes such as Fe(III)-succinate, Fe(III)--ketoglutarate, and Fe(III)-nicotianamine are somehow degraded when irradiated with synchrotron X-rays and Fe(III) can undergo photoreduction. Degradation of the organic molecules was assessed by HPLC-UV/Vis analyses on the same samples investigated by X-ray absorption spectroscopy (XAS). Fe speciation in xylem sap samples revealed Fe(III) to be complexed by citrate and acetate. Nevertheless, artifacts created by radiation damage cannot be excluded. The use of highly brilliant synchrotrons as X-ray sources for XAS analyses can dramatically increase the sensitivity of the technique for trace elements thus allowing their speciation in xylem sap. However, great attention must be paid to radiation damage, which can lead to biased results.
Keywords Iron . Synchrotron . XANES . Speciation . Xylem sap . Radiation damage
Introduction
It is widely accepted that the available pool of iron (Fe) in soil solution, especially within the rhizosphere, is represented by a mixture of Fe-complexes [1] with a variety of natural ligands (organic acids, phenolic compounds, siderophores...