For real sample analysis, 1 mL tap water or pool water was put into a 10 mL volumetric flask. Next, RATU (100 μL) and Hg2+ (25 μL, 75 μL or 90 μL) were added, diluted with H2O to volume, and the fluorescence spectrum was assayed. To determine the relative standard deviation (RSD), three samples were measured for each Hg2+ concentration.