Sensing of organic vapor adsorption on gold using a temperature insensitive microbalance

The adsorption of organic vapor molecules onto the gold electrode surface of a dual mode 10 MHz 3rd overtone SC-cut quartz crystal microbalance (QCM) was investigated. Using this dual mode QCM, the separation of mass and temperature change can be made in real time, with resolutions of 56 pg and better than 0.01 K, respectively. The QCM experiments were performed in a UV/ozone chamber so that the gold electrodes could be maintained in a clean state. Organic vapors or liquids (e.g., benzene, hexane, methanol, ethanol, isopropanol, or butanol) were injected into the chamber while the two modes of the dual mode QCM were monitored and the mass-frequency and temperature changes were extracted. This paper demonstrates the ability of the sensor to determine in a matter of seconds, sub-ppm (ppm/spl equiv/parts per million) gas concentrations of benzene and hexane while operating in an elevated temperature environment without any temperature stabilization. In addition, the mass changes for a series of adsorbed methanol, ethanol, isopropanol, and butanol were found to be proportional to molecular weights.