Gradient ion-pair chromatographic method for the determination of iron N,N′-ethylenediamine-di-(2-hydroxy-5-sulfophenylacetate) by high performance liquid chromatography–atmospheric pressure ionization electrospray mass spectrometry

The most effective remedy for iron deficiency is the use of synthetic iron chelates, specifically chelates derived from polyamine-carboxylic acids as EDDHSA (N,N′-ethylenediamine-di-(2-hidroxy-5-sulfophenylacetic) acid). A gradient ion-pair chromatographic method was developed to quantify the total amount of chelated iron in EDDHSA/Fe3+ fertilizers. Two mobile phases were used containing, respectively, 35 and 75% acetonitrile in a 0.005 M tetrabutylammonium hydroxide aqueous solution at pH 6.0. The stationary phase was a reverse phase C-18 column (150 mm × 3.9 mm i.d., dp = 5 μm). Two chromatographic peaks appeared and were identified by Electrospray Mass Spectrometry. The first peak corresponds to the monomer of EDDHSA/Fe3+ and the second peak has been assigned to condensation molecules. Quality parameters indicate that the method is suitable for the quantification of iron chelate by EDDHSA fertilizers.