Dispersive Liquid-Liquid MicroExtraction technique based on Solidification of a Floating Organic drop (DLLME-SFO) combined with flame atomic absorption spectrometry was developed for determination of thallium in water sample. An appropriate mixture of acetone and 1-undecanol was rapidly injected into an aqueous sample containing TlCl4- which forms an ion pair with brilliant green reagent and as a result a cloudy mixture was formed. After centrifugation, the test tube was cooled for 5 min and the solidified 1-undecanol drop formed on the top of the solution was transferred into a suitable vial and it was dissolved in 300µL of acetone and finally introduced into the flame atomic absorption spectrometer. Several factors affecting the extraction process, such as the volume of the extractant and disperser solvents, centrifugation time, concentration of brilliant green, concentration of HCl, ionic strength, volume of diluting solvent and interferences were studied. Under the optimum operating conditions, the calibration graph was linear in the range of 240-6000ng/mL with a limit of detection of 90 ng/mL and preconcentration factor was 17. The Relative Standard Deviation (RSD) for five replicate measurements of thallium was 3.6%. The accuracy of the method was assessed using a certified reference material (unalloyed zinc) and spiked tap water. The results demonstrated high accuracy, recovery and applicability of the presented method.

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