Selective and sensitive spectrophotometric method to determine trace amounts of copper metal ions using Amaranth food dye.

Copper is an essential element in some biological processes in organisms, so it was important to find ways to identify trace amounts of it. Minimal amounts of copper ions can be determined in aqueous solutions in the spectrophotometric method suggested in this study. The method depends on the reaction between Cu(II) and Amaranth dye at the pH 6.0. The gradual disappearance of Amaranth colour at 520 nm occurring with an increase of Cu(II) concentration from 0.13 up to 2.0 μg cm-3. The molar absorptivity coefficient and Sandell's sensitivity of the complex are found to be 0.94 × 104 L mol-1 cm-1, 6.8 ng cm-2 respectively. The advantages of this method are simple, selective, and highly sensitive. The method was used for determination of copper ions in aqueous solutions containing several metal ions, where excellent agreements between reported and obtained results were achieved in aqueous solutions containing copper metal ions only. The postulated method is in an excellent agreement with the determination of Cu(II) ion concentrations by atomic absorption spectroscopy (AAS). The interference was studied to determine the copper metal ions concentration, and do not interfere with eleven of other metal ions.