Usage of thiocyanate-based ionic liquid as new optical sensor reagent: Absorption and emission based selective determination of Fe (III) ions.

In this work, the ionic liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]) was evaluated for the first time for its probable usage as new optical sensor reagent for the determination of several metal ions. The ionic liquid exhibited a selective and sensitive response to iron ions in acidic aqueous solutions among all of the tested metal ions. The ([BMIM][SCN]) was encapsulated in ethyl cellulose (EC) matrix in the form of continuous thin films. The effect of [BMIM][SCN] concentration and pH to iron response, the fluorescence quantum yield, the absorption, emission and excitation based characteristics of the ionic liquid in presence of Fe and Fe ions were investigated in both EC and [BMIM][SCN]/aqueous buffer solution mixtures. As a result, the highly sensitive, selective and rapid responding optical sensor reagent which does not need any time-consuming extraction, oxidation and reduction procedures was presented for the distinguishing determination of Fe and Fe in both aqueous solutions and solid thin film matrix. The ionic liquid exhibited a better emission and absorption based response for Fe ions when compared with the Fe ions. The molar absorptivity constant in presence of ionic liquid-based SCN was enhanced 10 times to 1.21 × 10 L mol cm for Fe ions in the solution phase. Linear absorption and emission-based calibration graphs were obtained for a wide concentration range of 8.0 × 10-6.2 × 10 M and 8.0 × 10-6.2 × 10 M for Fe, respectively. Limit of detection (LOD) values for absorption and emission-based methods were 2.48 × 10 and 2.4 × 10, respectively. The reaction is instantaneous and absorbance remains stable for over 4 months.