Comparative study of colorimetric sensors based on newly synthesized Schiff bases

New sensitive cation receptors 2a and 2b containing oligoether linked Schiff bases were prepared and their ability to calorimetrically sense transition metal ions was investigated. Addition of metal ions to a methanol solution of 2a, 2b can result in an obvious colour change (from colourless to yellowish-brown for Cu2+ and colourless to yellow for Co2+, Ni2+, Cd2+, Zn2+) and UV–vis absorption spectral change in a short time. The colour change and binding ability of receptors with Cu2+ ion are more compare to other ions, the detection limit is allowable to 1.0 × 10−5 and 1.0 × 10−6 M level of Cu2+, 1.0 × 10−4 and 1.0 × 10−5 M level of Co2+, Ni2+, Cd2+, Zn2+ according to visual colour change and UV–vis spectral change, respectively. This indicated that these two receptors are highly selective for those metal ions over other ions like Ca2+, Mg2+, Mn2+, Hg2+, Cr3+, Fe2+, Pb2+.