172 Original Paper Soil & Water Res., 10, 2015 (3): 172–180 doi: 10.17221/256/2014-SWR Study of Interactions between Relevant Organic Acids and Aluminium in Model Solutions Using HPLC and IC Ondřej DRÁBEK 1 , Isaac KIPKOECH KIPLAGAT 1 , Michael KOMÁREK 2 , Václav TEJNECKÝ 1 and Luboš BORŮVKA 1 1 Department of Soil Science and Soil Protection, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Prague, Czech Republic; 2 Department of Environmental Geosciences, Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Prague, Czech Republic Abstract Drábek O., Kipkoech Kiplagat I., Komárek M., Tejnecký V., Borůvka L. (2015): Study of interactions between relevant organic acids and aluminium in model solutions using HPLC and IC. Soil & Water Res., 10: 172–180. The interactions of different organic acids such as citric, malic, oxalic, and fulvic with aluminium were studied using ion-exchange chromatography (IC) and high performance liquid chromatography (HPLC). The experi- ments were carried out at low pH (1.5–3.1). The results of IC experiments on the interaction between Al and oxalate, citrate, and malate were compared with model chemical equilibrium calculations. The strongest effect on Al speciation was observed with oxalic acid and fulvic acid. These two ligands formed more than one type of complex with Al. In contrast, there was no significant effect of malic acid on Al speciation and a rather weak effect caused by citric acid. The studies show that the formed complexes are stable even at low pH. Keywords: aluminium speciation; citric acid; fulvic acid; malic acid; oxalic acid Aluminium (Al) occurs ubiquitously in the terres- trial environment. It is the most abundant metal in the lithosphere, comprising about 8% of the Earth’s crust (Hendershot et al. 1996). Soil acidification may substantially mobilize and release Al into soil solu- tion, ground and surface waters. This phenomenon is emphasized particularly in poorly buffered soils (Ščančar & Milačič 2006). The released mononu- clear ionic Al species may undergo polymerization or may be complexed by available organic or inorganic ligands (Poléo 1995; Bi et al. 2004). In the soil solu- tion of an unacidified forest soil, about 80% of Al in the upper horizons is organically bound (Dahlgren & Ugolini 1989; Lundström & Giesler 1995). Soil solution contains a wide variety of organic substances including organic acids with the ability of forming complexes with Al. Among these acids, high molecular mass (HMM) acids are fulvic acids (FA). However, low molecular mass (LMM) organic acids like oxalic and citric acids are also present (Tipping 2005). Al speciation controls its mobility in the environment, bioavailability, and toxicity (e.g. Ma & Hiradate 2000). Al is recognized as a potentially toxic element for all living organisms including human beings (Exley & Korchazhkina 2001). In the case of toxicity towards plants it has been shown, by laboratory bioassay, that Al-organic binding can reduce or diminish Al toxicity (Alvarez et al. 1992). Moreover, organic acids play a key role in Al tolerance mechanisms. Some plants de- toxify Al in the rhizosphere by releasing organic acids that chelate Al (Jones et al. 2001). Hue et al. (1986) found that organic acids with hydroxyl and carboxyl groups are able to form stable ring structures with Al 3+ that consist of 5 or 6 bonds conferring the greatest protection from Al toxicity. Te secretion of organic acids is highly specifc to Al and the site of secretion is localized to the root apex (Ma & Hiradate 2000). Te kind of organic acids secreted as well as secretion pattern difer among plant species. Also internal de- toxifcation of Al in Al-accumulating plants is achieved