Increased sensor sensitivities obtained by polymer-coated quartz microbalances

Polymer-coated quartz microbalances were produced and studied. They exhibited high sensitivities for heavy noncyclical hydrocarbons and CO2 concentration measurements. Detection limit of 1 ppm CO2 and 10 ppm Shellsol (Shell solvent containing: 28.7% C10H22; 66.4% C11H24; 5% C12H26) are obtained and reported. The time constants of the absorption and desorption processes were investigated also. A diffusion-free behaviour was observed and related to the porosity of the layer. Collateral AFM (atomic force microscopy) analysis of the polymer structure was performed. We explain big values of the absorption–desorption time constant for CO2 and small values for CnH2n+2 mixtures in connection with the peculiarities of the chemical reaction involved by the sensing mechanisms.