3.3. Interferences
Because dithizone is a versatile chelating agent, interferences may occur due to the competition of other heavy metal ions for dithizone and their subsequent co-extraction with cadmium (II). To evaluate the selectivity of the proposed method, the effect of typical potential interfering ions was investigated and the results were shown inTable 1(tolerable limit was taken as a relative error ≤10%). According to the data, the major matrix ions in the natural water sample have no obvious interferences, while other heavy metal ions, which possibly competed with Cd (II) for the chelating agents, have less tolerable limits. If excessive amounts of foreign metal ions were present, higher concentration of dithizone may be used to weaken the competition effect. Considering the ultra sensitivity for the determinationof cadmium, proper dilutionof samples could effectively decrease the matrix effect