3D-printed carbon black-based electrode for simultaneous determination of ascorbic acid and kojic acid in dermo-cosmetic products

A miniaturized and disposable poly(lactic acid)-carbon black-based working electrode (3D CB-PLA) was developed using 3D printing technology through fused filament fabrication to be applied to the simultaneous analysis of the antioxidant compounds ascorbic acid (vitamin C) and kojic acid. A previous chemical/electrochemical activation of the 3D CB-PLA electrode was carried out in 1.0 mol L⁻¹ NaOH, applying a fixed potential of +1.0 V vs. Ag/AgCl, KCl_(sat) for 1800 s. This procedure was necessary to remove a smooth layer of PLA polymer on the electrode surface and to allow the carbon black conductive sites to be exposed. Morphological and spectroscopic characterizations performed before and after activation revealed a rougher surface with an increased presence of oxygenated functional groups, attributed to both the activation process and the enhanced exposure of carbon black. Using cyclic voltammetry in 0.1 mol L⁻¹ Britton-Robinson buffer (pH 7.0), the irreversible oxidation reactions of ascorbic and kojic acids were observed at +0.30 and +0.87 V vs. Ag/AgCl, KCl_(sat), respectively. With the experimental conditions optimized, calibration curves were constructed for both analytes by square wave voltammetry, with detection limits of 4.80 and 5.40 µmol L⁻¹ for ascorbic acid and kojic acid, respectively. The activated 3D CB-PLA electrode enabled accurate and precise simultaneous quantification of both antioxidant compounds in facial whitening creams, demonstrating its effectiveness and analytical potential.