This method describes the procedure for the ion chromatographic determination of the total amount of each of the individual ortho-ortho isomer of the chelating agents EDDHA and EDDHMA in fertilizers containing one or both of these substances. The method allows the identification and the determination of the total water soluble fraction of each of these chelating agents. It does not allow to distinguish between the free form and the metal bound form of the chelating agents.
NOTE 1 EDDHA and EDDHMA are abbreviations used in this standard for the sake of simplicity. For complete names see annex A.
NOTE 2 The substances EDDHA and EDDHMA exist under several different isomeric forms. Positional isomers (ortho, meta, and para forms) as well as stereo isomers (meso and dl forms) are known.
This method applies to fertilizers containing chelates of one or more of the following micro-nutrients: cobalt, copper, iron, manganese, zinc and with a mass fraction of at least 0,1 %.
NOTE 3 At present, analytically pure standards only exist for ortho-ortho EDDHA. All other substances being unavailable as a standard, the influence of their eventual presence in the samples (with respect to the sensitivity and the selectivity of this method) has not been studied. For EDDHMA, the method has been developed with samples of iron EDDHMA of uncertain purity and composition, any standard product being unavailable.
NOTE 4 In the chromatographic conditions of this method, the stereo isomers of EDDHA and EDDHMA are eluting together as a single peak. Using an eluent with a lower exchange strength, the meso and the dl forms of EDDHA and EDDHMA can be separated.