A portable platform with integrated colorimetric and electrochemical detection of nitrite and bisulfite in...

Monitoring nitrite and bisulfite in environmental waters, beverages, and food products is highly relevant due to their regulatory limits and potential risks to human health. Existing analytical techniques often face limitations such as high cost, long analysis times, and environmental impact. In this study, a new colorimetric-electrochemical method was developed for the detection and quantification of nitrite and bisulfite, integrating bromocresol green (BG) as a colorimetric reagent with square-wave voltammetry (SWV) using laboratory-fabricated screen-printed graphite electrodes (SPE-Gr) and a 3D-printed platform. The method provides dual analytical information: a visible color change from yellow to blue/green and distinct electrochemical signals that enable the simultaneous identification of both analytes. The system requires low sample volumes (60 µL), supports portability, and is suitable for on-site applications with a low cost per analysis ($1.72). Under optimized conditions, linear responses were obtained in the ranges of 10-60 µmol L^-1 for nitrite and 50-500 µmol L^-1 for bisulfite, with limits of detection equal to 1.68 and 14.5 µmol L^-1, respectively. The electrochemical response showed good stability across replicate and independent SPE-Gr devices (RSD < 2% for E_p and < 5% for I_p). Overall, the proposed methodology combines rapid screening with reliable quantification (recoveries of 90-145% and 71-113% for nitrite and bisulfite, respectively), providing a practical and selective alternative for environmental and beverage samples.