This European Standard specifies a method for the chromatographic determination of the chelating agent [S,S]-EDDS in fertilizers. The method allows the identification and the determination of the total concentration of the water-soluble fraction of this chelating agent. It does not allow distinguishing between the free form and the metal bound form of the chelating agent.
This method is applicable to EC fertilizers containing chelates of one or more of the following micro-nutrients: cobalt, copper, iron, manganese and zinc, covered by Regulation (EC) No 2003/2003 [4]. It is applicable to a mass fraction of the metal chelated of at least 0,35 %.
NOTE 1 The substance EDDS (ethylenediamine-N,N'-disuccinic acid) exists as several different stereo isomeric forms. [S,S] (with CAS Number 20846–91–7), [R,R] and [R,S] optical isomers are possible. [S,S] and [R,R] are mirror images with equal chemical characteristics. However only the [S,S] isomer is biodegradable. When both are present, they form the racemic mixture. The [R,S] isomer (the meso isomer) is only slowly biodegradable.
Only the [S,S]-EDDS isomer is allowed by the Regulation (EC) No 2003/2003. Since the Cu chelate of the [R,R]-EDDS isomer presents the same stability than the [S,S]-EDDS, both should coelute. The absence of [R,S]-EDDS indicates that only a pure isomer ([S,S] or [R,R]) exist. An additional test based on polarimetry can be used to ascertain the isomeric characteristic of the sample, or the standard.