ORIGINAL PAPER Piotr Stepnowski Solid-phase extraction of room-temperature imidazolium ionic liquids from aqueous environmental samples Received: 12 October 2004 / Accepted: 26 October 2004 / Published online: 23 December 2004 Ó Springer-Verlag 2004 Abstract Owing to their favorable properties, ionic liq- uids have recently gained recognition as possibly envi- ronmentally benign solvents. Now among the most promising industrial chemicals, they have already been labeled ‘‘green’’, but this appellation seems due entirely to their very low vapor pressure. This growing interest in the various applications of ionic liquids will soon result in their presence in the environment. Therefore, reliable analytical tools for the environmental analysis of ionic liquids need to be developed urgently. This paper pre- sents a newly developed analytical procedure for the enrichment of 1-alkyl- and 1-aryl-3-methylimidazolium ionic liquids from water samples. The method is based on cation exchange solid-phase extraction followed by selective elution. Pre-concentrated samples are subjected to high-performance liquid chromatography (HPLC) with an advanced methodology for qualitative and quantitative analysis. The overall procedure was verified by using standard spiked samples of tap water, seawater, and freshwater. Keywords Ionic liquids Æ Analysis Æ SPE Æ Cation exchange Æ Environmental samples Introduction In recent years, room-temperature ionic liquids have increasingly attracted attention as the green, high-tech reaction media of the future. Typical ionic liquids con- sist of an organic cation with a delocalized charge and an organic or inorganic fluoro anion. The dispropor- tionately large, bulky organic cations with a low degree of symmetry, such as N-alkylpyridinium or 1-alkyl-3- methylimidazolium, tend to reduce the lattice energy of the crystalline form of the salt and hence lower the melting point. These ionic solvents possess numerous fascinating properties and are of fundamental interest to modern chemistry and the chemical industry; this is mainly as a result of their lack of vapor pressure, high conductivity, wide tuneability regarding hydrophobicity, polarity, solvent solubility and miscibility, as well as high thermal stability [1–4]. The application of ionic liquids as reaction media for organic synthesis, catalysis, or biocatalysis is well documented, and their synthesis has been reviewed [3, 5–9]. However, the thermody- namics and kinetics of the reactions carried out in these neoteric solvents are different from those in conven- tional molecular solvents; hence their chemistry is dif- ferent and unpredictable, given the current state of knowledge [9]. Additionally, there is still a conspicuous lack of knowledge about such questions as their toxicity, eco-toxicity, bioaccumulation, environmental chemistry, eco-kinetics, and distribution in the environment. Pio- neering work in these fields [10–12] has already indicated that further research aiming towards a better under- standing of the environmental properties and the pro- spective risk assessment of ionic liquids is a matter of urgency. Therefore, the development of new analytical methods for the rapid and reproducible separation and identification of ionic liquids is a prerequisite for future biological and environmental research into these sub- stances. The direct analysis of the cationic constituents of ionic liquids from aqueous samples has been already reported. A method for reversed-phase high-perfor- mance liquid chromatography (HPLC) with electro- spray mass detection was developed and applied to biological samples [13]. A systematic study of the sepa- ration of imidazolium ionic liquids using ionic chroma- tography has also been performed [14]. Ionic liquid cations and related imidazole derivatives have also been separated by alpha-cyclodextrin-modified capillary electrophoresis [15]. More recent work has focused on a capillary electrophoretic method for resolving selected P. Stepnowski Faculty of Chemistry, University of Gdan´sk, ul. Sobieskiego 18/19, 80-952 Gdan´sk, Poland E-mail: sox@chem.univ.gda.pl Tel.: +48-58-3450448 Fax: +48-58-3450454 Anal Bioanal Chem (2005) 381: 189–193 DOI 10.1007/s00216-004-2932-3