River water and lake water were gotten from Xier River and Erhai Lake (Dali, China). All the real water samples above were filtered through a 0.25 μm micropore member and acidified to pH about 5.0 with HAC-NaAC buffer solution prior to use. Tap water was collected in our laboratory after flowing for about 5 min. Commercialmineral water was purchased in the local market. To further validate the accuracy of the proposed method, some certified reference samples such as food and water of different cadmium and copper concentrations were selected for the determination, which were purchased from National Standard Center of China. Closed-vessel microwave digestion was chosen for decomposing the food samples and the digestion procedure
was based on a reference method for corn [27]. While water samples were prepared by simple dilution of the certified reference water samples to suitable concentration in the linear dynamic range of the method. The resultant digests/dilution were then subjected to DLLME
and subsequently analyzed by spectrophotometer.