Cross sensitivity effects of volatile organic compounds on a SAW-based elemental mercury vapor sensor

The detection of anthropogenic elemental mercury (Hg0) is the first step for evaluating the efficiency of mercury removal technologies implemented in many industrial processes. In order to determine the feasibility of a Hg0 vapor sensor for real world applications, it is very important to study the cross sensitivity performance of the sensor toward Hg0 vapor in the presence of common gas species present in industrial effluents. In this paper, we report the cross-sensitivity effect of several common VOCs; Ethylmercaptan (EM), Dimethyl Disulfide (DMDS) and Methyl Ethyl Ketone (MEK) on a surface acoustic wave (SAW) based sensor, when measuring low concentrations (<400 ppbv) of Hg0 vapor at operating temperatures of 35 and 75 °C. The sensor response magnitudes toward the tested Hg0 vapor concentrations (calibration curve) were found to follow the Langmuir extension isotherm at both operating temperatures (R2 > 0.98) indicating that the developed sensor is well designed to detect low concentrations of Hg0 vapor. In fact, the limit of detection (LOD) of the developed sensor toward Hg0 vapor was found to be ~2.6 and ~1 ppbv at 35 and 75 °C, respectively, which are well below the current threshold exposure limit set by the World Health Organization (5.6 ppbv). Moreover, the sensor showed excellent repeatability (95 ± 1%) at both operating temperatures. When tested for its selectivity toward Hg0 vapor in the presence of other gaseous species, the sensor exhibited a loss in response magnitude of only up to 7%; thus indicating the sensor has excellent selectivity toward Hg0 vapor and can potentially be used for online monitoring of low concentrations of Hg0 vapor within industrial processes and stack effluents.