A selectively rhodamine-based colorimetric probe for detecting copper(II) ion

A novel rhodamine derivative 3-bromo-5-methylsalicylaldehyde rhodamine B hydrazone (BMSRH) has been synthesized by reacting rhodamine B hydrazide with 3-bromo-5-methylsalicylaldehyde and developed as a new colorimetric probe for the selective and sensitive detection of Cu²⁺. Addition of Cu ²⁺ to the solution of BMSRH results in a rapid color change from colorless to red together with an obvious new band appeared at 552 nm in the UV-vis absorption spectra. This change is attributed to the spirocycle form of BMSRH opened via coordination with Cu²⁺ in a 1:1 stoichiometry and their association constant is determined as 3.2 × 10⁴ L mol^-1. Experimental results indicate that the BMSRH can provide a rapid, selective and sensitive response to Cu²⁺ with a linear dynamic range 0.667-240 μmol/L. Common interferent ions do not show any interference on the Cu²⁺ determination. It is anticipated that BMSRH can be a good candidate probe and has potential application for Cu²⁺ determination. The proposed probe exhibits the following advantages: a quick, simple and facile synthesis.