Ionic liquid-based zinc oxide nanofluid for vortex assisted liquid liquid microextraction of inorganic mercury in environmental waters prior to cold vapor atomic fluorescence spectroscopic detection

• ZnO nanofluid based vortex assisted liquid liquid microextraction was developed.
• Hg2+ in waters was extracted prior to CV-AFS detection.
• Free from dispersive solvent and no requirement of back extraction.
• The method is simple, fast, inexpensive and environmental friendly.

Zinc oxide nanofluid (ZnO-NF) based vortex assisted liquid liquid microextraction (ZnO-NF VA-LLME) was developed and employed in extraction of inorganic mercury (Hg2+) in environmental water samples, followed by cold vapor atomic fluorescence spectrometry (CV-AFS). Unlike other dispersive liquid liquid microextraction techniques, ZnO-NF VA-LLME is free of volatile organic solvents and dispersive solvent consumption. Analytical signals were obtained without back-extraction from the ZnO-NF phase prior to CV-AFS determination. Some essential parameters of the ZnO-NF VA-LLME and cold vapor generation such as composition and volume of the nanofluid, vortexing time, pH of the sample solution, amount of the chelating agent, ionic strength and matrix interferences have been studied. Under optimal conditions, efficient extraction of 1 ng/mL of Hg2+ in 10 mL of sample solution was achieved using 50 μL of ZnO-NF. The enrichment factor before dilution, detection limits and limits of quantification of the method were about 190, 0.019 and 0.064 ng/mL, respectively. The intra and inter days relative standard deviations (n=8) were found to be 4.6% and 7.8%, respectively, at 1 ng/mL spiking level. The accuracy of the current method was also evaluated by the analysis of certified reference materials, and the measured Hg2+ concentration of GBW08603 (9.6 ng/mL) and GBW(E)080392 (8.9 ng/mL) agreed well with their certified value (10 ng/mL). The method was applied to the analysis of Hg2+ in effluent, influent, lake and river water samples, with recoveries in the range of 79.8–92.8% and 83.6–106.1% at 1 ng/mL and 5 ng/mL spiking levels, respectively. Overall, ZnO-NF VA-LLME is fast, simple, cost-effective and environmentally friendly and it can be employed for efficient enrichment of the analyte from various water samples.

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