Ion-pair Solid-Phase Extraction of Trace Amounts of Ionic Liquid Cations in Fresh and Seawater Samples

The usefulness of ion-pair reagents in selective solid reversed-phase extraction of one N-butyl-4-methylpyridinium and four short-chain alkylimidazolium ionic liquid cations from aqueous media was investigated using various concentrations of alkylsulfonates with different alkyl chain lengths. Final recoveries of the two cations with the shortest alkyl residues were poorer than those of the other, more hydrophobic compounds. Moreover, the recovery values were little affected by the different concentrations of the reagents. In nearly all cases, the best recoveries were obtained with the 2-heptanesulfonate reagent. The analytical performance parameters included excellent linearity over four orders of magnitude, with limits of detection ranging from 0.01 to 0.06 ppm, and very good precision and accuracy. The method was successfully used to extract ionic liquids from spiked seawater and freshwater samples. Recoveries and limits of detection were quite similar to those obtained with preconcentrated standard solutions.