Smartphone-Enabled Copper(II) Ion Quantification with an Optical Platform and Image Processing Algorithm

Copper(II) ions, Cu(II), were quantified using a smartphone camera and an optical platform designed to measure the turbidity changes of a solution. An aqueous solution with Cu(II) ions was mixed with dithiooxamide chelate, which forms particles of barely soluble copper dithiooxamide, Cu(dto), chelate polymer. The mixture was placed in a transparent sample container, and the intensity of light transmitted through the solution was captured as an image using a smartphone camera. The images obtained were analyzed by a custom image-processing algorithm, which enabled transformation of the image data from RGB (red, green, blue) to HSV (hue, saturation, value) color space and calculation of a mean value of the light-intensity component, known as the V value. The V value was proportional to the concentration of Cu(II) ions in a sample, based on a previously determined standard calibration curve obtained with the same optical platform and smartphone camera settings. The results obtained with the smartphone-enabled method were cross-validated using UV-vis spectroscopy and inductively coupled plasma mass spectrometry. The linearity range of the method was 0.22-15 mg/L, and the relative standard deviation (RSD) (%) value was 1.2-9% (for n = 10). The limit of detection (LOD) of the method was 0.30 mg/L, which is below the World Health Organization (WHO) maximum recommended copper(II) concentration for drinking water (2 mg/L). The limit of quantification (LOQ) was 0.89 mg/L.