Digital images for colorimetric determination of copper in dietary supplements

This study proposes a digital image analysis-based procedure for the determining copper content in dietary supplements. The method was established by measuring the color of the copper(II)-salicylic acid complex. Digital images obtained during analysis were captured using a smartphone equipped with the ColorMeter® application, which provided corresponding RGB (Red, Green, Blue) color values. The experimental chemical conditions were optimized using multivariate experimental design, and the optimal parameters were determined. The proposed method was validated, and the limits of detection (LD) and quantification (LQ), and precision for the RGB channels were established. A comparison with ultraviolet-visible (UV/Vis) spectroscopy results revealed no statistically significant differences at a 95% confidence level. The proposed method was applied to ten dietary supplement samples, which exhibited copper content ranging from 278 ± 13 to 3530 ± 75 µg (R channel) and 268 ± 14 to 2706 ± 275 µg (G channel). The mean values obtained showed excellent agreement with the values declared by manufacturers on product labels. These results demonstrate that the proposed method is suitable for copper determination in dietary supplements using digital images.