A Sensitive and Selective Method for Visual Chronometric Detection of Copper(II) Ions Using Clock Reaction

We report a visual chronometric method for the detection of copper(II) ions (Cu2+) using the clock reaction between methylene blue (MB) and hydrazine (N2H4). The addition of Cu2+ greatly accelerates the clock reaction due to the formation of the Cu cluster between Cu2+ and N2H4. By recording the change of the reaction time and solution color, different concentrations of Cu2+ in buffer and environmental water have been detected. As low as 300 nM Cu2+ can be visually identified by the naked eye without the assistance of any advanced instruments. This visual chronometric assay shows a dynamic range from 0.2 to 16 μM with a limit of detection of 20 nM. Additionally, it has good selectivity toward Cu2+ and against other common metal cations.