Visual detection of perchlorate in aqueous solution using alkali methylene blue

Perchlorate (ClO 4 − ) has aroused wide concern as a global ecosystem pollutant, especially in the aquatic environment. A rapid and visible detection of ClO 4 − in aqueous solution using alkali methylene blue (MB) and liquid–liquid extraction (LLE) was established with high selectivity and sensitivity. The alkali MB exclusively change from red into blue in an organic solvent when exposed to aqueous ClO 4 − . The organic solvent, amount of MB and the alkalinity of the solution were systematically optimized, while the underlying mechanism was revealed using UV–Vis spectroscopy and mass spectrometry. Under the optimum conditions, the UV–Vis absorbance at 600 nm showed a good linear relationship with the concentrations of ClO 4 − in the range of 0.0025–0.025 mM ( R 2 = 0.9945). The visual detection limit was 0.005 mM in environmental water and 0.02 mM in black tea infusion. This method provides an economical and simple visual detection of ClO 4 − in an aqueous solution. Graphical abstract