Separation and preconcentration system based on microextraction with ionic liquid for determination of copper in water and food samples by stopped-flow injection spectrofluorimetry

In this work, an efficient in situ solvent formation microextraction (ISFME) was combined with stopped-flow injection spectrofluorimetry (SFIS) for the determination of copper. In the proposed approach, thiamine was oxidized with copper(II) to form hydrophobic and highly fluorescent thiochrome (TC), which was subsequently extracted into ionic liquid as an extractant phase. A small amount of an ion-pairing agent (NaPF6) was added to the sample solution containing a water-miscible ionic liquid ([Hmim][BF4]) to obtain a hydrophobic ionic liquid ([Hmim][PF6]), which acted as the extraction phase. After centrifuging, phase separation was performed and the enriched analyte was determined by SFIS. ISFME is an efficient method for separation and preconcentration of metal ions from aqueous solutions with a high ionic strength. Variables affecting the analytical performance were studied and optimized. Under optimum experimental conditions, the proposed method provided a limit of detection (LOD) of 0.024 μg L−1 and a relative standard deviation (RSD) of 2.1%. The accuracy of the combined methodology was evaluated by recovery experiments and by analyzing certified reference material (GBW 07605 Tea). Finally, the proposed method was successfully applied to copper determination in water and food samples.