Rapid and sensitive analysis of microcystins using ionic liquid-based in situ dispersive liquid–liquid microextraction

• IL-based in situ DLLME was coupled to HPLC-MS in the analysis of microcystins.
• The IL structures were optimized to enhance selectivity toward microcystins.
• LODs for MC-RR and MC-LR were achieved at low part-per-trillion level.
• High accuracy of the analytical method was demonstrated using tap and river water.

Three structurally different ionic liquids (ILs), namely 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), 1-(6-hydroxyethyl)-3-methylimidazolium chloride ([HeOHMIM][Cl]) and 1-benzyl-3-(2-hydroxyethyl)imidazolium bromide ([BeEOHIM][Br]), were applied as extraction solvents using in situ dispersive liquid–liquid microextraction (in situ DLLME) for the preconcentration of two microcystin variants, microcystin-RR (MC-RR) and microcystin-LR (MC-LR) from aqueous samples. Extraction parameters including sample solution pH, ratio of IL to metathesis reagent, sample volume, IL quantity, and salt concentration were optimized to achieve the best extraction efficiency. The [BeEOHIM][Br] IL, which contains both an aromatic moiety and a hydroxyl group within its chemical structure, exhibited superior extraction efficiency compared to the other two ILs. The analytical performance of the [BeEOHIM][Br] IL as an extraction solvent for in situ DLLME of microcystins was investigated using HPLC-UV and HPLC-MS. The limits of detection (LODs) for MC-RR and MC-LR were 0.7 μg L−1 using UV detection with a linear range from 1 to 50 μg L−1. The separation method was successfully adapted for ESI-MS/SIM detection, wherein the LODs for MC-RR and MC-LR were greatly improved to 0.005 and 0.003 μg L−1, respectively. The accuracy of the method was demonstrated by examining the relative recovery using tap water and river water and produced recoveries ranging from 45.0 to 109.7% and from 46.3 to 103.2%, respectively.