Xuanwu Lake water was sampled from Xuanwu Lake in Nanjing, China and tap water was collected from the local supply system in Nanjing, China. Before use, the lake water wasfiltered through a 0.45μm membranefilter (Tianjin, China). The pH value of the two water samples were both adjusted to 6.5 and 9.1, respectively. The pH of Certified Reference Material of Environment Water (GBW08607) was adjusted to 6.5 and 9.1 respectively after 1000 fold dilution