Temperature-controlled ionic liquid dispersive liquid–liquid microextraction combined with fluorescence detection of ultra-trace Hg2+ in water

Abstract

Significant efforts have been devoted to developing trace-level quantification of Hg²⁺. In this work, a novel fluorescence detection (FD) approach combined with preconcentration of Hg²⁺ in ionic liquid (IL), N-octylpyridinium tetrafluoroborate ([OPy]⁺[BF₄]⁻), was developed for the determination of trace Hg²⁺ in water. The temperature-controlled ionic liquid dispersive liquid–liquid microextraction (TC-IL-DLLME) technique was used to improve the enrichment factor. After extraction and centrifugal separation, precipitated IL was diluted with water and acetonitrile containing the fluorescent probe. Under optimum conditions, the photoluminescence intensity of the fluorescence emission peak was found to be linear with the concentration of Hg²⁺ in the range from 0.1 to 0.5 μg L⁻¹. The limit of detection for the TC-IL-DLLME-FD method was calculated to be 0.0342 μg L⁻¹ (S/N = 3). Further, the selectivity of the sensor was measured by evaluating its response to other heavy-metal ions and was shown to be excellent. Recoveries were assessed by spiking water samples with different Hg²⁺ standard stock solutions, giving satisfactory recoveries from 80 to 110%.