Two D-π-A Schiff-Base-Functionalized Silica Gel Adsorbents for Preconcentration of Copper Ions in Foods and Water for Detection

Copper is an essential element in many biological processes and plays an important role in carbohydrate and lipid metabolism. Excess or deficiency of Cu ions can cause disturbances in cellular homeostasis and damage the central nervous system. Here, for the first time, two functionalized silica gel (SG-A and SG-B) adsorbents were prepared and tested for copper detection via the reactions of chlorinated silica gel with two novel D-π-A Schiff base compounds: 2-amino-3-(quinolin-2-ylmethyleneamino)maleonitrile (A) and 2-(4-(diethylamino)-2-hydroxybenzylideneamino)-3-aminomaleonitrile (B) in the thionyl chloride solution, respectively. SG-A and SG-B as adsorbents filled in a microcolumn were used to enrich trace Cu ions in foods and water with the detection of flame atomic absorption spectrometry. Because of the strong coordination between two D-π-A Schiff base compounds and Cu ²⁺ ions, the stable heterocyclic Cu ²⁺ -SG-A/B complex is formed. For a sample volume of 30 mL, detection limits of 0.09 μg L ^-1 and 0.15 μg L ^-1 have been achieved. The results of selectivity study show that the two adsorbents can selectively extract Cu ²⁺ in complex matrixes with other metal cations. The methods have been successfully applied to the determination of Cu ²⁺ content in various real samples, and the detection sensitivity that we report here is better than most results reported using modified silica gels.