Gas sensing with zeolite-coated quartz crystal microbalances—principal component analysis approach

Three different zeolites, which are zeolite A, silicalite-1 and sodalite, were deposited on quartz crystal microbalance (QCM) oscillators with fundamental resonance frequency of 4.7 MHz. Three QCMs, as well as one without zeolites as a reference, were exposed to single gases such as NO, SO2 and H2O in He at 443 K. The frequency shifts and their differential values to time were measured, and both of them are tested to elucidate which is more useful to quanlify and quatify these single gases using principal component analysis (PCA). Based on these results, mixed gases of NO and SO2 in several compositions in He are examined. Mixed-gas data are also qualified and quantified using PCA. These results suggest that the sensor system with the differential values which represent sorption-kinetics, instead of the frequency shifts representing sorption-equilibria, overcame the disadvantages of the conventional QCM sensors and showed favorable qualification and quantification performances for the gas mixture.