A paper-based analytical device for rapid colorimetric detection of aluminium in aerosol antiperspirants†

This work focuses on developing a simple and low-cost methodology for colorimetric analysis of aluminum in aerosol antiperspirants using paper-based analytical devices (PADs). The devices were manufactured by combining a layer of paper with two layers of pouch film, consisting of 35 circular zones with a diameter of 6 mm each. Subsequently, analytical parameters were optimized by capturing the colorimetric responses of the reaction between aluminium (III) and Eriochrome Cyanine R in proportions of 3 μL of Eriochrome Cyanine R in the concentration of 1.5 g L⁻¹ to 7 μL of aluminium solution. The effect of impregnating the paper with three different nanomaterials to improve the PAD response was also evaluated. With the help of a smartphone and an app capable of analyzing color generated from photos, the analytical curve was established in the concentration range from 1 to 6 mg L⁻¹, achieving a LOD of 0.52 mg L⁻¹ and a LOQ of 1.56 mg L⁻¹, with the modification of the paper with multi-walled carbon nanotubes. Subsequently, aluminium levels in aerosol antiperspirant brands were analyzed by evaluating different sample preparation methods. The results were compared with those obtained by performing the analyses using Microwave Plasma-Atomic Emission Spectroscopy (MP-AES), revealing statistically comparable results, and the recovery assay achieved recoveries ranging from 91.7 to 105.9%. Among the innovations brought by this work are the testing of new methods for preparing aerosol antiperspirant samples and the first application of the proposed modified PAD. There is the possibility of performing chemical analyses in environments with few resources and opening opportunities for many applications.