Dual-headspace microfluidic paper-based analytical device for rapid and simultaneous determination of sulfite and...

This work presents a novel dual-headspace microfluidic paper-based analytical device (μPAD) designed for simultaneous determination of sulfite and ethanol in wine. The device integrates two independent headspace chambers, each tailored for gas-phase separation and selective sensing of the target analyte. This design enables both analytes to be determined in a single sample drop without cross-interference, using distinct detection strategies in parallel. Upon sample introduction, sulfite reacts with a pre-stored acid in one chamber to generate SO_2(g), which diffuses through the headspace and is partially absorbed into a moistened detection zone. A capacitively coupled contactless conductivity detector (C4D) then records real-time conductivity changes due to H⁺_(aq) and HSO₃^-_(aq) formation. Simultaneously, ethanol in another headspace chamber volatilizes into the second detection zone, where it reduces pre-deposited dichromate reagent, resulting in a visible color change. The colorimetric signal is analyzed via smartphone imaging and ImageJ software. The device achieves linear calibration ranges of 8-100 mg L^-1 for sulfite and 0-8 % (v/v) for ethanol, with detection limits (3SD of regression/slope) of 6.35 mg L^-1 and 1.18 % (v/v), respectively. The analysis is completed within 5 min, using a single disposable μPAD that is compact, low-cost, and suitable for on-site wine testing. The device was successfully validated with real wine samples, offering a practical alternative for rapid sulfite and ethanol monitoring.