Preconcentration and Trace Determination of Chromium Using Modified Ionic Liquid Cold-Induced Aggregation Dispersive Liquid–Liquid Microextraction: Application to Different Water and Food Samples

An efficient microextraction procedure based on modified ionic liquid cold-induced aggregation dispersive liquid–liquid microextraction (M-IL-CIA-DLLME) was developed for trace determination of chromium in water and food samples by flame atomic absorption spectrometry (FAAS), and it was used for speciation of Cr(III) and Cr(VI) in water samples by using Na2SO3 as the reducing agent. A mixture of water-immiscible 1-hexyl-3-methylimidazolium hexafluorophosphate ([Hmim][PF6]) ionic liquid (IL) (microextraction solvent) and ethanol (disperser solvent) were directly injected into a heated aqueous solution containing bis(2-methoxy benzaldehyde) ethylene diimine as a Schiff’s base ligand (chelating agent), hexafluorophosphate (NaPF6; as a common ion) and Cr(III). Afterwards, the solution was placed in an ice-water bath and a cloudy solution was formed due to a considerable decrease of IL solubility. After centrifuging, the sedimented phase containing enriched analyte was determined by FAAS. Under the optimum conditions, the calibration graph was linear over the range of 2–50 μg L−1 with limit of detection of 0.7 μg L−1. The accuracy of the present methodology was tested by recovery experiments and by analyzing a certified reference material. Relative standard deviation (RSD %) was 2.7 % for Cr(III). The proposed method was successfully applied for trace determination of chromium in water and food samples.