Smartphone-assisted paper-based colorimetric analytical platform for simultaneous determination of barium and strontium ions

Heavy metal contamination especially in aqueous media has become an important risk to human health and environment. Therefore, due to the broad distribution of barium (Ba²⁺) and strontium (Sr²⁺) ions in the environment and wide variety of their harmful health effects for human, development of efficacious systems for their accurate and selective determination is of great importance. Aiming to develop a point-of-care and easy-to-use sensing device, a paper-based colorimetric sensing device was designed for simultaneous measurement of Ba²⁺ and Sr²⁺ ions standing on the basis of the color change of sodium rhodizonate (SR) in the presence of various concentrations of the target analytes. These color changes were photographed using a smartphone, and after analyzing with Photoshop 2022 software, the average variations in the intensities of colors (RGB (red, green, blue) model) were used to draw the calibration curves. The quantitative identification of Ba²⁺ and Sr²⁺ ions in a single solution was carried out by masking one of them at a moment. The average color intensities (G) displayed a linear relationship with the concentration of the analytes in the ranges of 5––300 ppm and 5–350 ppm with the limit of detection (LOD) values of 3.64 and 4.75 ppm for Ba²⁺ and Sr²⁺ ions, respectively. Moreover, the selectivity of the proposed analytical device was assessed; SR was selective for the target analytes versus the other ions causing a considerable color change. Furthermore, the practical application of this colorimetric device was investigated by the excellent performance in real samples indicating its potential for field applications.

Graphical abstract