Smartphone Digital Image Colorimetry for the Determination of Aluminum in Antiperspirant Products.

Objectives: 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).

Materials and methods: 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.

Results: 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.

Conclusion: The proposed method was successfully applied for the determination of aluminum in APPs with percentage recoveries ranging from 80.0 to 109.6%.