Synthesis of a quinoxaline–hydrazinobenzothiazole based probe—single point detection of Cu2+, Co2+, Ni2+ and Hg2+ ions in real water samples

Abstract

A novel quinoxaline–hydrazinobenzothiazole based sensor was synthesized and characterized using NMR, FTIR, and Mass spectroscopy techniques. The sensor achieves the distinct “single-point” colorimetric and fluorescent detection of Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions with distinguishable color changes from yellow to red, pale red, pale brown and orange, respectively. The UV-visible and fluorescence emission spectral investigation revealed the excellent single-point sensing ability of the probe towards four different heavy metal ions with a ratiometric response. Nanomolar levels of detection of about 1.16 × 10⁻⁷ M, 9.92 × 10⁻⁸ M, 8.21 × 10⁻⁸ M, and 1.14 × 10⁻⁷ M for Cu²⁺, Co²⁺, Ni²⁺ and Hg²⁺ ions, respectively, were achieved using our sensor, which are below the US-EPA permissible limits. Additionally, the sensor was utilized for naked eye detection under normal daylight. Quantitative determination of the metal ions in real water samples was also demonstrated.