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(38-64) Analytical methods for assessment of Al species in soil solutions and their uptake by plants. Milačič, Radmila*,1, Polak, Tjasa Bantan1, Mitrovic, Bojan1, 1 Jožef Stefan Institute, Ljubljana, Slovenia ABSTRACT- Al chemistry depends strongly on pH. Positively charged aqua- and hydroxy-monomeric forms were found to be the most toxic Al species. In aqueous solutions spectrophotometry and chelating ion-exchange chromatography offer determination of the sum of positively charged lablie Al species. Cation-exchange FPLC-ICP-AES procedure developed in our group is much more selective and enables determination of Al3+, Al(OH)2+ and Al(OH)2+ species. In complex matrices all these techniques suffer from interferences of various inorganic and organic Al complexes. On the basis of the specific selectivity of particular technique and comparison of analytical data it was demonstrated that in aqueous extracts of forest soils Al exists predominantly as monomeric species bound to organic molecules. Combination of size-exclusion chromatography with UV and ICP-AES detection and cation-exchange FPLC-ETAAS provided more complex information. About 40% of monomeric Al is bound to humic complexes, the remaining Al exists as AlF2+, Al-oxalate and Al-citrate species, but these species were not quantified. Al-citrate and some other carboxylate Al complexes play and important role in the environment. However, there was a lack of reliable analytical techniques for their speciation. In our group an analytical procedure was developed for quantitative determination of Al-citrate and some other low molecular weight (LMW) Al complexes by anion-exchange FPLC - ETAAS. The characterisation of LMW-Al species was performed not only on the basis of the retention time (ETAAS detection), but also by ES-MS-MS analysis. The technique was applied in speciation of LMW-Al complexes in plant sap and in the investigation of the uptake of various Al species in the Brasica rapa pekinesis. Speciation analyses were performed in the nutrient solution treated with various Al species. The results indicate that 70% of Al3+ added to the nutrient solution was transformed in roots to Al-malate. Al-citrate and Al-malate added to the nutrient solution were transferred to the upper parts of the plant without transformation of their chemical forms. Combination of complementary speciation techniques is necessary and enables a reliable interpretation of analytical data to be made. Key words: Al speciation, Combination of various speciation techniques, Soil extracts, Plants |
