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

ABSTRACT

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 Fe3+ and Fe2+ 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 Fe3+ and Fe2+ in both aqueous solutions and solid thin film matrix. The ionic liquid exhibited a better emission and absorption based response for Fe3+ ions when compared with the Fe2+ ions. The molar absorptivity constant in presence of ionic liquid-based SCN- was enhanced 10 times to 1.21 × 104 L mol-1 cm-1 for Fe3+ ions in the solution phase. Linear absorption and emission-based calibration graphs were obtained for a wide concentration range of 8.0 × 10-8-6.2 × 10-4 M and 8.0 × 10-8-6.2 × 10-5 M for Fe3+, respectively. Limit of detection (LOD) values for absorption and emission-based methods were 2.48 × 10-5 and 2.4 × 10-8, respectively. The reaction is instantaneous and absorbance remains stable for over 4 months.