Dispersive liquid-liquid microextraction based on ionic liquid and spectrophotometric determination of mercury in water samples

A new simple and rapid dispersive liquid-liquid microextraction based on ionic liquid (IL) has been applied for the first time to preconcentrate trace levels of mercury as a prior step to its determination by spectrophotometric detection. In this method, small amount of an IL (1-hexyl-3-methylimmidazolium bis(trifluormethylsulfonyl)imid) as the extraction solvent was dissolved in acetone as the disperser solvent and the binary solution was then rapidly injected by a syringe into the water sample containing Hg cations which were complexed by 4,4'-bis(dimethylamino)thiobenzophenone (TMK) in the presence of sodium dodecyl sulphate as the anti-sticking agent. Thereby, a cloudy solution was formed and the Hg-TMK complex was extracted into the fine IL droplets. After centrifuging, the droplets of extractant were settled at the bottom of a conical test tube and the extracted phase was determined by spectrophotometry at 575 nm. Usually some parameters affect the complex formation and extraction, such as the type and volumes of extraction and disperser solvents, type and concentration of anti-sticking agent, salt concentration, pH and concentration of chelating agent, which have also been optimised for the presented method. Under optimum conditions, the enrichment factor of 18.8 was obtained from 10 mL of water. The detection limit of the method was found to be 3.9 g L-1 and the relative standard deviation (n = 5) for 50 g L-1 of mercury was 1.7%.