Amount of Copper(II) Ions in a Solution Cannot Be Determined Using the Hue Values

Conventional mobile phone colorimetry usually utilizes the RGB color mode to measure concentration of solutions, but the paper entitled "Determining the Amount of Copper(II) Ions in a Solution Using a Smartphone" proposes the use of hue (H) to measure the concentration. It is pointed out that the H value increases with the increase of copper nitrate concentration. However, our experimental results show that the H value does not change with the concentration, which indicates that the amount of copper ions in a solution cannot be determined by H values. The errors in the paper may come from the deficiencies of materials and methods, resulting in large deviations.