CHROMATOGRAPHIC SEPARATIONS OF METAL-CHELATES PRESENT IN COMMERCIAL FERTILIZERS .2. DEVELOPMENT OF AN ION-PAIR CHROMATOGRAPHIC-SEPARATION FOR THE SIMULTANEOUS DETERMINATION OF THE FE(III) CHELATES OF EDTA, DTPA, HEEDTA, EDDHA AND EDDHMA AND THE CU(II), ZN(II) AND MN(II) CHELATES OF EDTA

The determination of the iron(III) chelates of EDTA, DTPA, HEEDTA, EDDHA and EDDHMA and the Cu(II), Zn(II) and Mn(II) chelates of EDTA by ion-pair chromatography has been investigated. Addition of the ion-pairing reagent tetrabutylammonium hydroxide to the mobile phase gave rise to a separation of all iron(III) chelates on a Chromspher C-18 column. A solvent-switching system was used to achieve this separation. The switching sequence was 5 min mobile phase A (0.05 M TBAOH, pH 7.5), 20 min mobile phase B (0.05 M TBAOH, pH 7.5, 30% acetonitrile) and 25 min mobile phase A. For the iron(III) chelates, both limit of determination and linear range studies showed that the method is capable of analysing the concentration ranges found in commercial fertilisers. The Cu(II), Zn(II), and Mn(II) chelates of EDTA were separated using 0.01 M tetradecyltrimethylammonium bromide, 0.01 M KH2PO4, pH 7.5.