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. Commercialmineralwater
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.