USING TEMPERATURE-CONTROLLED IONIC LIQUID-LIQUID PHASE MICROEXTRACTION METHOD FOR EFFICIENT PRE-CONCENTRATION OF CHROMIUM IONS PRIOR TO THE DETERMINATION BY HIGH RESOLUTION-CONTINUUM SOURCE FLAME ATOMIC ABSORPTION SPECTROMETRY

In this study, an efficient and simple pre-concentration procedure was proposed for the determination of chromium (VI) ions in water samples. A hydrophobic ionic liquid (1-octyl-3-methylimidazolium hexafluorophosphate or in brief [C8MIM] [PF6]) was used as extractant solvent. This ionic liquid (IL) was chosen among the other counterparts considering its high hydrophobicity, which facilitates complete separation of it from the aqueous phase. Dispersion of [C8MIM] [PF6] in aqueous phase was made just by controlling the temperature at its optimum value, without using an organic dispersant solvent. At first, chromium (VI) was complexed with ammonium pyrrolidine dithiocarbamate (APDC) as a chelating agent, then a very small amount of [C8MIM] [PF6] was dispersed in water sample at optimum temperature, instantly the complex of Cr (VI)-APDC was extracted into the fine droplets of ionic liquid phase. Determination step was made using a high resolution continuum-source flame atomic absorption spectrometer. Some important parameters such as temperature, volume of chelating agent, pH, amount of ionic liquid, centrifugation time and rate were investigated. Under optimum conditions, the calibration graph was linear (R = 0.9975) in the range of 0.04 to 2.0 μg mLˉ. The limit of detection (3σ) of the proposed method was 0.01 μg mLˉ and the relative standard deviation for seven replicated determinations of 1.0 μg mLˉ Cr (VI) was 1.03%.