Conductometric determination on microfluidic thread-based analytical device for near-real-time ammonia detection in exhaled breath.

This work aims to develop a microfluidic cotton thread-based analytical device (μCTAD) as a membraneless micro scrubber for gas sampling and in-situ conductometric detection of ammonia. The μCTAD cell comprises treated cotton, without further modification, that contacts two stainless-steel rod electrodes inside the gas sampling cavity. The device serves as a micro-gas collector, utilizing 50 mmol L-1 boric acid as an absorbing solution for the detection of NH3. The analyte gas was passed through the μCTAD cell, where it cames into direct contact with a liquid film flowing over the cell and was then measured by conductometric detection for in-situ analysis. Various related parameters influencing the conductometric detection of NH3, such as gas flow rate and humidity, were investigated. Under optimized conditions, a linear range of 56 - 370 ppbv of NH3 gas was achieved, with a limit of detection (LOD, 3SDb) of 2.4 ppbv. The repeatability of the conductivity signal was 1.7% relative standard deviation. The proposed μCTAD was demonstrated and applied to the detection of NH3 in human exhaled breath, enabling non-invasive health monitoring. This device offers several advantages over a conventional online membrane-based diffusion scrubber coupled with fluorometric detection.