Determination of ionic liquid cations in soil samples by ultrasound-assisted solid-phase extraction coupled with liquid chromatography-tandem mass spectrometry
Liquid chromatography-tandem mass spectrometry coupled with an ultrasonic-assisted extraction and solid phase extraction procedure has been investigated for the separation and detection of imidazolium, pyridinium, pyrrolidinium, ammonium and phosphonium-based ionic liquid (IL) cations in soil samples. First, the samples were extracted with acetonitrile–0.2 mol L−1 ammonium chloride solution (8 : 2, v/v; pH 3) using an ultrasonic assisted extraction procedure and then eluted on a Strata-X-CW solid-phase extraction column. The target compounds were effectively separated with an Agilent SB-C18 (1.88 μm, 3.0 mm × 100 mm) chromatographic column by gradient elution, in which acetonitrile–water (containing 0.1% formic acid) acted as the mobile phase. The IL cations were determined by electrospray positive ionization (ESI+) combined with multiple reaction monitoring (MRM) mode, and quantified by the matrix-matched external standard method. The limits of detection (LODs) ranged from 0.15 to 2.88 ng g−1 and the limits of quantification (LOQs) from 0.50 to 9.50 ng g−1. The average recoveries of the twenty-three IL cations in soil samples were in the range of 69.3–106.8%, with relative standard deviations of 2.17–12.1%. This assay showed greater sensitivity and accuracy, to meet the requirements of the determination of IL cations in soil.