Direct incorporation of babassu biochar into graphite conductive ink for the voltammetric determination of flunixin using a screen-printed electrode.

The development of sustainable electrochemical sensors based on renewable carbon materials has gained increasing attention within the framework of Green Analytical Chemistry. In this work, a screen-printed electrode (SPE) was fabricated using a lab-made conductive ink composed of graphite (Gr) and babassu-derived biochar (BBC), employing nail polish as a low-cost binder. The incorporation of BBC directly into the conductive ink provided improved electrochemical performance compared to the unmodified electrode, with the composition containing 2.5% BBC showing the best analytical response. The electrochemical behavior of flunixin (FNX), a widely used non-steroidal anti-inflammatory drug in veterinary medicine, was investigated using square-wave voltammetry (SWV). Under optimized conditions, the proposed SPE-Gr/BBC sensor exhibited a linear response in the concentration range of 0.25-40 μmol L-1, with a detection limit of 0.07 μmol L-1. The sensor demonstrated good repeatability (RSD < 4.0%) and inter-electrode reproducibility (RSD < 5.0%). Selectivity studies indicated satisfactory tolerance toward most evaluated coexisting species. The applicability of the proposed platform was evaluated through the determination of FNX in commercial veterinary pharmaceutical formulations and synthetic serum samples, yielding recoveries between 97.3% and 110% and showing good agreement with a spectrometric reference method. In addition, the environmental profile of the analytical procedure was assessed using the AGREE metric, yielding a score of 0.81 and indicating favorable alignment with the principles of Green Analytical Chemistry. The results demonstrate that the direct incorporation of BBC into conductive inks represents a simple strategy for fabricating electrochemical sensors based on biomass-derived carbon materials.