ISOCRATIC ION-PAIR HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC METHOD FORTHE DETERMINATION OF VARIOUS IRON(III) CHELATES

The micronutrient iron, an essential element for plant growth, is usua lly added as fertilizer in chelated form. An isocratic ion-pair chroma tographic method was developed to identify and determine the total amo unt of chelate in fertilizers. Iron(III) chelates containing ethylened iaminetetraacetic acid, diethylenetriaminepentaacetic acid, trans-1,2- cyclohexanediaminetetraacetic acid, ethylenediaminedi(o-hydroxyphenyla cetic) acid (EDDHA), also known as N,N'-ethylenebis-2-(o-hydroxyphenyl )glycine, ethylenediaminedi(o-hydroxy-p-methylphenylacetic) acid, s(2- hydroxybenzyl)ethylenediamine-N,N'-dipropionic acid and -bis(2-hydroxy benzyl)ethylenediamine-N,N'-diacetic acid were well separated by this method. The mobile phase contained 0.03 M tetrabutylammonium chloride and 30% acetonitrile at pH 6.0. The stationary phase was a LiChrospher RP-18 column, the injection volume was 20 mu 1 and the flow-rate was 1.5 ml/min. For the iron(III)-EDDHA chelate, linear range studies show ed that the method is capable of determining Fe concentrations between 0.5 and 150 mu g/ml, which permits the determination of the concentra tions found in commercial fertilizers. With this method, separation an d identification of the iron(III) complexes were obtained with good re solution and selectivity, including the separation of the geometric is omers of the complexes, in 15 min.