Determination of long-chained alkylimidazolium ionic liquids based on the hypochromic effect

Abstract

The hypochromic effect of bromocresol green (BCG) resulted from long-chained imidazolium ionic liquids was investigated. The hypochromic effect may be caused by the formation of the neutral complex [C_nmim]₂⁺[BCG]²⁻via electrostatic interaction and hydrophobic interaction. Based on the spectral characteristics, a new method for determination of long-chained imidazolium ionic liquids is developed. The proposed method can be performed using a UV-vis spectrophotometer, at the optimum λ_min. Beer's law is obeyed in the concentration range of 0.004–0.04 mmol L⁻¹ for [C₁₄mim]Br and [C₁₆mim]Cl, and the detection limits are 0.0011 and 0.00095 mmol L⁻¹ for [C₁₄mim]Br and [C₁₆mim]Cl, respectively. Meanwhile, precision, accuracy and tolerance are also very good. The method is fast, economical and does not require organic solvents; it can be applied for determination of long-chained imidazolium ionic liquids.