Hollow fiber supported ionic liquid membrane microextraction for speciation of mercury by high-performance liquid chromatography-inductively coupled plasma mass spectrometry

Abstract

With an ionic liquid as the membrane liquid and dithizone as the carrier, a novel and simple hollow fiber supported liquid phase microextraction (HF-LPME) method was developed for the preconcentration and determination of monomethylmercury (MMHg) and inorganic mercury (IHg) in environmental water samples by high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The parameters affecting the enrichment factors, including the type of ionic liquid membrane and carrier, the pH of the sample solution, the concentration of L-cysteine in the acceptor phase, stirring rate, extraction temperature and time, were optimized. With the optimal extraction conditions (ionic liquid membrane phase: [C₄MIM][PF₆] with 0.02% (m/v) dithizone; acceptor phase: 25 μL, 1 g L⁻¹L-cysteine; extraction temperature: 50 °C; extraction time: 12 h), the obtained enrichment factors of MMHg and IHg were 1620 and 1540, and the detection limits for MMHg and IHg were 0.3 ng L⁻¹ and 0.9 ng L⁻¹, respectively. There was no significant effect on the extraction efficiency in the presence of humic acid (0–25 mg L⁻¹ dissolved organic carbon). The proposed method was applied to real water samples, and the spike recoveries obtained were in the range 90.8–108.2%. These results demonstrate that the proposed ionic liquid based HF-LPME-HPLC-ICP-MS method is a simple and sensitive technique for the determination of mercury species at trace levels in water samples, with a high reproducibility and accuracy.