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Application of response surface methodology for optimization of ionic liquid-based dispersive liquid–liquid microextraction of cadmium from water samples

A new, rapid, and simple method for the determination of cadmium in water samples was developed using ionic liquid-based dispersive liquid–liquid microextraction (IL-DLLME) coupled to flame atomic absorption spectrometry (FAAS). In the proposed approach, 2-(5-boromo-2-pyridylazo)-5-(diethyamino) phenol was used as a chelating agent and 1-hexyl-3-methylimidazolium bis(trifluoro methylsulfonyl)imide and acetone were selected as extraction and dispersive solvents, respectively. Sample pH, concentration of chelating agent, amount of ionic liquid (extraction solvent), disperser solvent volume, extraction time, salt effect, and centrifugation speed were selected as interested variables in IL-DLLME process. The significant variables affecting the extraction efficiency were determined using a Placket–Burman design. Thereafter, the significant variables were optimized using a Box–Behnken design and the quadratic model between the dependent and the independent variables was built. The optimum experimental conditions obtained from this statistical evaluation included: pH: 6.7; concentration of chelating agent: 1.1 × 10− 3 mol L−1; and ionic liquid: 50.0 mg. Under the optimum conditions, the preconcentration factor obtained was 100. Calibration graph was linear in the range of 0.2–60 µg L−1 with correlation coefficient of 0.9992. The limit of detection was 0.06 µg L− 1, which is lower than other reported approaches applied to the determination of cadmium using FAAS. The relative SD (n = 8) was 2.4%. The proposed method was successfully applied to the determination of trace amounts of cadmium in the real water samples with satisfactory results.