Paper-based microfluidic devices for electrochemical quantification of the explosive picric acid

A high-throughput analytical method for quantifying the explosive picric acid (PA) is reported. The approach first involves developing a three-electrode thermoplastic chip, which was then integrated with circular paper structures to generate microfluidic paper-based analytical devices (µPADs). The electrochemical setup was fabricated using a 3D printing pen, a tool commercialized as a toy for kids. The electrochemical chips were initially tested using differential pulse voltammetry to promote the analyte's reduction. After evaluating the PA electrochemical behavior, the µPADs were assembled using a practical procedure with clamps and filter paper. The µPAD assembly was optimized by evaluating the paper substrate, injection volume, and detection potential. Larger-pore papers resulted in a superior response due to greater accessibility of the analyte solution to the electrode surface during injection. Increasing the injection volume enhanced the signal intensity, besides providing better repeatability. Increasing the detection potential enhances the system response. However, this parameter affects selectivity as other species could also be reduced on the electrode surface. Under optimal conditions, the proposed system enabled the sequential injection of an analyte solution into a single device, yielding a sample throughput of (131 ± 14) injections h^-1. Furthermore, a linear response was obtained from 10 to 100 µmol L⁻¹ picric acid, with a limit of detection of 5.0 µmol L^-1. Moreover, the system's applicability was further demonstrated for lake water analyses through recovery studies. Therefore, this work reports a practical analytical tool for the PA quantification in environmental analyses.