Alizarin Complexone as a highly selective ratiometric fluorescent probe for Al3+ detection in semi-aqueous solution

Abstract A simple and selective spectrofluorimetric method for the determination of trace levels of aluminum has been developed using Alizarin Complexone (AC). Exhibiting absorption and fluorescence changes in the presence of Al 3+ in EtOH–H 2 O solution at pH 4.6, AC could be used as a colorimetric and fluorescent chemosensor for the detection of Al 3+ . In the presence of Al 3+ ions, AC undergoes fluorescence quenching at 487 nm and shows the formation of a new red-shifted band at 558 nm. A good linear relationship could be obtained between the fluorescence intensity ratio ( I 487 / I 558 ) and the concentration of Al 3+ ions in the range of 0.3–4.5 × 10 −5  M ( R 2  = 0.9825). The intensity changes allow a ratiometric detection of Al 3+ in acid semi-aqueous solution with the detection limit of 5.2 × 10 −7  M. Moreover, the colorimetric and fluorescent response of AC to Al 3+ can be conveniently detected by the naked eye, which provides a facile method for visual detection of Al 3+ . The optimized ground state geometry and corresponding UV–vis absorption spectral characteristics of AC and AC·Al 3+ complex have also been calculated using Density Functional Theory (DFT) with CEP-31G basis sets.