Combination of various analytical techniques for speciation of low molecular weight aluminium complexes in plant sap

The possibilities for speciation of low molecular weight aluminium organic acid complexes (LMW-Al) in plant sap were investigated by applying a combination of various chromatographic and spectroscopic techniques. The behavior of different LMW-Al complexes was investigated in synthetic aqueous solutions on anion and cation exchange fast protein liquid chromatography (FPLC) columns with inductively coupled plasma – atomic emission spectrometry (ICP-AES) or electrothermal atomic absorption spectrometry (ETAAS) detection. Plant sap of Sempervivum tectorum with a high concentration of Al (9.3 μg cm^–3) and Sansevieria trifasciata with an appreciably lower Al concentration (0.065 μg cm^–3) were analyzed. The speciation study in plant sap indicated that the species present in these samples, existed as negatively charged LMW-Al complexes which were eluted at the retention time typical for Al-citrate and Al-aconitate. In order to identify Al binding ligands eluted under the chromatographic peak analysis by electrospray ionization (ESI)-MS technique using Z spray ion source were also applied. The predominant LMW-Al negatively charged complexes in Sempervivum tectorum and Sansevieria trifasciata were found to be Al-citrate and Al-aconitate. It was shown that other LMW organic acids do not form complexes with Al in the samples studied.