Detection of Hexavalent Chromium by Copper Sulfide Nanocomposites.

Chromium (Cr) is a vital environmental contaminant. In environmental matrixes, Cr presents dominantly in hexavalent chromium [Cr(VI)] and trivalent chromium [Cr(III)], which are two different inorganic states. Cr(VI) is a well-known human carcinogen, while Cr(III) is a naturally occurring micronutrient for the human body. Hence, speciation of Cr is crucial for ensuring environmental water and food safety. The distinction between each chromium species is almost impossible with commonly used methods like atomic spectrometric techniques, due to the low level of Cr and the high complexity of the matrix. Typically, a preconcentration step is required prior to determining and improving the selectivity and detection limit of the inspection instrument. For this process, nanocomposites, which are emerging high-quality adsorbents are used. However, preparation of previous nanocomposites suffered from a trivial synthesis process, had high reagent consumption, and was time-consuming. Therefore, we succinctly designed and fabricated the novel triadic silica gel-supported copper sulfide (CuS) nanocomposites for ultrasensitive detection of Cr(VI). CuS nanocomposites in a solid phase system were successfully applied to extract Cr(VI) in reference materials, such as food and water samples. Cr(VI) were detected by use of flame atomic absorption spectrometry (FAAS). By loading 30 mL of sample solution, a linear range of 0.5-300 µg L-1 with R = 0.998, a detection limit of 0.15 µg L-1, and an accuracy of 1.7% (20 µg L-1, n = 11) were obtained by this method. The detection limit and the precision of this procedure are superior to those reported in the literature with the same detection technique, indicating that CuS nanocomposites have a good potential for Cr(VI) detection which is essential for food safety and human health.

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 Cu2+ ions, the stable heterocyclic Cu2+-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 Cu2+ in complex matrixes with other metal cations. The methods have been successfully applied to the determination of Cu2+ content in various real samples, and the detection sensitivity that we report here is better than most results reported using modified silica gels.