Speciation of 2′-deoxymugineic acid–metal complexes in top soil extracts by multi-modal stationary phase LC-ICP-MS
2′-Deoxymugineic acid (DMA) is a principal representative of phytosiderophores exuded by graminaceous plants in response to iron limiting soil conditions. In the present work a method for selective quantification of metal–DMA complexes has been developed enabling us to investigate the interplay of DMA with transition metals at the root–soil interface, i.e. the rhizosphere. Chromatographic separation was performed via gradient elution preserving complex integrity at pH 6.6 in 55 mM ammonium acetate and 10% methanol on a mixed-mode reversed phase/weak anion exchange stationary phase. Quantification of the DMA–complexes of Fe, Co, Cu, Ni, Mn and Zn in soil related matrices was performed via an ICP-MS utilizing dynamic reaction cell technique with methane as reaction gas. Limits of detection and quantification were obtained in the range of 10 to 120 nM and 40 to 400 nM, respectively. Long term precision of the method was <10% relative standard deviation (n = 10). The suitability of the method for the metal–DMA complex speciation was evaluated within three calcareous soil extracts exhibiting various metal abundances. Prior to this, the top soil solutions were spiked with 100 μM DMA to induce the complex formation. Metal complexes of DMA in a concentration range of 0.4 to 30 μM were detected.