A comparison of surface acoustic wave (SAW) and quartz crystal microbalance (QCM) based sensors for portable, online mercury vapour sensing

The development of effective elemental mercury (Hg 0 ) vapour sensor is required to monitor the efficiency of Hg 0 removal technologies within industrial processes. In this paper, two different mass based transducers; surface acoustic wave (SAW) and quartz crystal microbalance (QCM) based Hg 0 vapour sensors were tested simultaneously in order to compare the performance of the two transducer platforms in real time. The sensors were tested towards low concentrations (24 to 365 ppbv) of Hg 0 vapour at close to room temperature (35°C). It was found that the SAW based sensor had up to 80 times higher response magnitude than the QCM based sensor when exposed to the Hg 0 vapour concentrations tested. The calculated coefficient of variance (COV) for both the SAW and QCM based sensors were found to be equivalent to ±5 ppbv and ±7 ppbv, respectively when tested towards a Hg 0 vapour concentration of 104 ppbv. The results indicated that the SAW based sensor had a lower limit of detection (LOD) of ~2.6 ppbv, whereas the QCM had a LOD of ~8ppbv.