The environmental samples including tap water, ground water, ice and snow were collected from Beijing, the Tibetan Plateau and Macao. The specific information for sample collection is as follows: Tap water was collected from Macao. Ground water was collected from Haidian District in Beijing. Snow samples 1–3 were collected from different residential areas near our laboratory. Ice samples 1 and 2 were collected from the Tibetan Plateau. All samples were stored in a refrigerator at 4uC before analysis. Before the samples were run on the IC system, they were subjected to a series of processes including filtration using 0.22 mm nylon membrane, elimination of sulphate and
chloride using On-Guard Ba and Ag–H column and 20 ml of the sample was concentrated online. In the preconcentration process the pretreated samples or standards were introduced into the concentrator column (AG19) by DX-300 at a flow-rate of 2.0 mL/min for 10 min. Each sample was injected in triplicate.