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

• A new approach for the determination of Al3+ in semi-aqueous solution is reported.
• Alizarin Complexone (AC) was used as the probe.
• AC exhibits ratiometric and colorimetric fluorescent selectivity for Al3+.
• The color changes between AC with Al3+ can be observed by the naked eye.
• AC is sensitive to Al3+ with detection limit of 5.2 × 10−7 M.

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 Al3+ in EtOH–H2O solution at pH 4.6, AC could be used as a colorimetric and fluorescent chemosensor for the detection of Al3+. In the presence of Al3+ 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 (I487/I558) and the concentration of Al3+ ions in the range of 0.3–4.5 × 10−5 M (R2 = 0.9825). The intensity changes allow a ratiometric detection of Al3+ in acid semi-aqueous solution with the detection limit of 5.2 × 10−7 M. Moreover, the colorimetric and fluorescent response of AC to Al3+ can be conveniently detected by the naked eye, which provides a facile method for visual detection of Al3+. The optimized ground state geometry and corresponding UV–vis absorption spectral characteristics of AC and AC·Al3+ complex have also been calculated using Density Functional Theory (DFT) with CEP-31G basis sets.