Journal of Chromatography A, 789 (1997) 453–460 Chromatographic determination of commercial Fe(III) chelates of ethylenediaminetetraacetic acid, ethylenediaminedi( o - hydroxyphenylacetic) acid and ethylenediaminedi( o -hydroxy-p - methylphenylacetic) acid a b a, * ´ L. Hernandez-Apaolaza , P. Barak , J.J. Lucena a ´ Agricultural Chemistry Department, Faculty of Sciences, Universidad Autonoma de Madrid, 28049 Madrid, Spain b Department of Soil Science, University of Wisconsin-Madison, Madison, WI, USA Abstract The use of synthetic iron chelates is the most common and effective way to treat iron chlorosis in plants. Using an ion-pair HPLC method previously proposed by the authors, it was found that the older commercial products reached the percentage of Fe chelated indicated by the manufacturer, but in no case did the current products reach their nominal, or legal, composition. Moreover, the current products of Fe–ethylenediaminedi( o-hydroxyphenylacetic) acid (FeEDDHA) showed significant additional chromatographic peaks that, based on published synthesis pathways for these type of compounds, may correspond to para – para FeEDDHA or ortho – para FeEDDHA, sterically-hindered isomers of FeEDDHA which are of little or no value as an iron chelate for agricultural purposes.  1997 Elsevier Science B.V. Keywords: Fertilizers; Metal chelates; Iron; Ethylenediaminetetraacetic acid; Ethylenediaminedi(hydroxyphenylacetic) acids 1. Introduction than the cost of application [4]. It is therefore necessary to evaluate the effectiveness of the com- For many crops, iron chlorosis is a major obstacle mercial products as well as to determine the most to crop production in calcareous soils. Iron normally suitable chelate from a purely chemical standpoint. exists in nature in either ferrous or ferric form. The The most common synthetic chelating agents used 31 solubility of Fe changes 1000-times with each pH to hold Fe are the polyamine-carboxylic acids, which unit change [1]. Among all methods used to correct form ferric complexes of high stability [1,5–8]. In iron chlorosis, synthetic iron chelates are currently, Europe, the 76 / 116 / EC directive allows chelates of but for their cost, the first choice for remediation of the elements Fe, Mn, Cu, Zn, and Co to be used as iron deficiencies in plants [2]. Metal chelates are such or incorporated in mixed fertilizers. Six chelat- used for micronutrient fertilization in foliar, trunk ing agents, all polyamine-carboxylic acids, are per- and soil application and in hydroponic cultures. Iron mitted for this purpose: EDTA (ethylenediamine- is by far the most common element used in fertilizers tetraacetic acid), DTPA (diethylenetriaminepen- in chelated form [3]. Nevertheless, sometimes the taacetic acid), HEDTA (hydroxy-2-ethylenediamine increased profit from using synthetic chelates is less triacetic acid), EDDHA [ethylenediaminedi( o-hy- droxyphenylacetic) acid, also known as EHPG: * Corresponding author. N,N9 - ethylene - bis - 2 - ( o - hydroxyphenyl)glycine], 0021-9673 / 97 / $17.00  1997 Elsevier Science B.V. All rights reserved. PII S0021-9673(97)00673-0