A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base sensor for expeditious detection of Al3+ and HSO3− in aqueous media

Abstract

A reversible fluorescent-colorimetric imino-pyridyl bis-Schiff base receptor L(N¹E,N⁴E)-N¹,N⁴-bis(pyridine-4-ylmethylene)benzene-1,4-diamine for the detection of both Al³⁺ and HSO₃⁻ in aqueous medium has been developed. Receptor L exhibits an excellent selective fluorescent-colorimetric response toward Al³⁺. The sensitivity of the fluorescent based assay (0.903 μM) for Al³⁺ is far below the limit recommended in the World Health Organization (WHO) guidelines for drinking water (7.41 μM). From ¹H NMR data, the Job plot and the ESI-MS spectrum, 1 : 2 stoichiometric complexation between L and Al³⁺ has been established. Receptor L shows remarkable detection ability in a wide pH range of 4–11 and was successfully utilised in the determination of Al³⁺ in aqueous solution of bovine serum albumin protein, and of HSO₃⁻ in real food samples. Moreover, L shows a highly selective colorimetric response to HSO₃⁻ by changing its colour from yellow to colorless immediately without any interference from other anions.