Determination of synthetic ferric chelates used as fertilizers by liquid chromatography-electrospray/mass spectrometry in agricultural matrices

11 pages, 5 figures, 4 tables.-- PMID: 17010641 [PubMed].-- Available online Sep 28, 2006.A high-performance liquid chromatography-electrospray ionization/mass spectrometry (time of flight) method has been developed for the simultaneous determination of synthetic Fe(III)-chelates used as fertilizers. Analytes included the seven major Fe(III)-chelates used in agriculture, Fe(III)-EDTA, Fe(III)-DTPA, Fe(III)-HEDTA, Fe(III)-CDTA, Fe(III)-o,oEDDHA, Fe(III)-o,pEDDHA, and Fe(III)-EDDHMA, and the method was validated using isotope labeled 57Fe(III)-chelates as internal standards. Calibration curves had R values in the range 0.9962–0.9997. Limits of detection and quantification were in the ranges 3–164 and 14–945 pmol, respectively. Analyte concentrations could be determined between the limits of quantification and 25 μM (racemic and meso Fe(III)-o,oEDDHA and Fe(III)-EDDHMA) or 50 μM (Fe(III)-EDTA, Fe(III)-HEDTA, Fe(III)-DTPA, Fe(III)-CDTA and Fe(III)-o,pEDDHA). The average intraday repeatability values were ~0.5 and 5% for retention time and peak area, respectively, whereas the interday repeatability values were ~0.7 and 8% for retention time and peak area, respectively. The method was validated using four different agricultural matrices, including nutrient solution, irrigation water, soil solution, and plant xylem exudates, spiked with Fe(III)-chelate standards and their stable isotope-labeled corresponding chelates. Analyte recoveries found were in the ranges 92–101% (nutrient solution), 89–102% (irrigation water), 82–100% (soil solution), and 70–111% (plant xylem exudates). Recoveries depended on the analyte, with Fe(III)-EDTA and Fe(III)-DTPA showing the lowest recoveries (average values of 87 and 88%, respectively, for all agricultural matrices used), whereas for other analytes recoveries were between 91 and 101%. The method was also used to determine the real concentrations of Fe(III)-chelates in commercial fertilizers. Furthermore, the method is also capable of resolving two more synthetic Fe(III)-chelates, Fe(III)-EDDHSA and Fe(III)-EDDCHA, whose exact quantification is not currently possible because of lack of commercial standards.This work was supported by the Spanish Ministry of Science and Education (MEC) (projects AGL2003-1999 and AGL2004-0194, cofinanced with FEDER) and the Commission of European Communities (project Isafruit). IO and AA-F were supported by a CONAID-DGA predoctoral fellowship and a "Ramón y Cajal" research contract from the Spanish MEC, respectively. Acquisition of the HPLC-MS(TOF) apparatus was cofinanced with FEDER.Peer reviewe