Highly sensitive and selective naked-eye detection of Cu2+ in aqueous medium by a ninhydrin–quinoxaline derivative

A simple ninhydrin–quinoxaline based colorimetric receptor 1 was designed, synthesized and characterized. The same exhibited high sensitivity and selectivity towards Cu2+ in aqueous medium (ethanol:H2O, 1:9, v/v) over a wide variation of cations such as Na+, Mg2+, Al3+, Co2+, Fe3+, Ni2+, Zn2+, Cd2+, Hg2+ and Pb2+. The addition of Cu2+ to the receptor 1 solution gave clear colour change from olive green to pink. The detection limit of receptor 1 was found to be 3.43 × 10−7 M which is probably the lowest one for the Cu2+ in an aqueous solution by any naked-eye receptor till date. The sensitivity and specificity of receptor 1 towards Cu2+ along with control compound receptor 2 were investigated in detail. This is only the second report where ninhydrin is used for the construction of any colorimetric sensor.