Detection of Hazardous Vapors Including Mixtures in Varied Conditions Using a Surface-Acoustic-Wave Device

A surface-acoustic-wave (SAW) sensor was used to detect gaseous chemical compounds ammonia, methane and their mixtures in varied environmental conditions. The sensing chamber was improved using top-cover PMMA with 200-mu L fluidic channels, compared with a traditional 1-L four-neck bottle. Small concentrations of ammonia (approximate to 250 ppb) and methane (approximate to 9 ppm) were detectable with this SAW sensor array with a sensing film, PNVP with mesoporous carbon hollow nanospheres. Tests of the stability and repeatability showed that the noise of the frequency change is about +/- 12.5 Hz within 410 s; the signal loss is less than 9% after 16 detection cycles. According to the results of the sensing measurements, the frequency shift of the ammonia/methane mixture was equivalent to the sum of the frequency shifts of ammonia and methane. In highly humid conditions the loss of signal of ammonia was much larger than that of methane. Based on the results of quantitative measurements of ammonia/methane gaseous mixtures, we found that the superposition effect between sensing signals for ammonia and methane was useable to predict the signal intensity for ammonia/methane gaseous mixtures at varied relative concentrations. (C) The Author(s) 2018. Published by ECS.