This study aims to present a method for the determination of the aluminum in antiperspirant products (APPs) by chelating it with quercetin before its detection by smartphone digital image colorimetry (SDIC). Samples were prepared by closed-vessel acid digestion in PTFE cups. This was followed by complexation of aluminum in the sample solution using quercetin as a chelating agent. Sample solutions were transferred into a quartz ultraviolet/visible detection microcuvette for detection in a homemade colorimetric box designed for capturing images of the yellow complex with a smartphone camera. The pixel intensity of the images was converted to numbers for quantitation using ImageJ software for a personal computer. An independent study using high-performance liquid chromatography-diode-array detection was conducted to check the accuracy of the proposed method. Optimum SDIC conditions included a Samsung C9 smartphone as the detection camera, a cropped region of interest of 6400 px², and the side position of the colorimetric box were selected for capturing the images of the sample solutions placed 10.0 cm from the detection camera, whereas optimum complexation conditions were found to be as sample pH of 5.5, sample volume of 3.0 mL, complexation time of 1.0 min and a ligand concentration of 0.28 mmol L^-1. Analytical performance of the method included a limit of detection of 0.5 μmol L^-1 and a coefficient of determination (R²) of the calibration graph of 0.9981. The proposed method was successfully applied for the determination of aluminum in APPs with percentage recoveries ranging from 80.0 to 109.6%.

Colorimetric determination of proteins in serum is proposed based on the biuret method and replacing ultraviolet-visible spectrometric (UV-Vis) detection with a simple and affordable smartphone digital image colorimetric (SDIC) method. Optimum SDIC conditions were found as a detection wavelength of 555 nm, a region of interest of 1600 px², and 9.0 cm between the detection camera and sample solution. Under the optimum conditions, the coefficient of determination was 0.9982 within a linear dynamic range of 0.022 to 0.35 g dL⁻¹. The precision of the method based on the percent relative standard deviation was below 5%. The limit of detection and limit of quantitation were found to be 0.007 and 0.022 g dL⁻¹ respectively, which were sufficient for the quantification of the total protein, albumin, and globulin in serum. The method was validated with an independent experiment using a UV-Vis method and both methods showed good statistical agreement, indicating the accuracy of the proposed SDIC method.