Studies of thin film chemical sensors using the quartz crystal microbalance

The quartz crystal microbalance (QCM) is emerging as a powerful new tool in sensor technology. In the course of this work, the QCM is used to study solvent and ion transport in poly(vinyl chloride) (PVC) ion-selective electrode (ISE) membranes and as a base for thin film analytical sensors for specific ionic species in solution.; Thin (approximately 1.5{dollar}mu{dollar}m) PVC-based ISE membranes can be easily attached to the QCM. When these membranes swell is solution due to solvent and/or ion uptake, the resultant mass change in the film causes the resonant frequency of the quartz crystal to decrease. The frequency measurements obtained when exposing ISE-type membranes containing neutral carrier type ionophores to analyte-containing solutions allow one to approximate the mass of solvent and analyte ions that entered the films during sensor operation. QCM mass measurements and conductance analysis of the membranes evaluated in this study indicate that they are extensively hydrated, implying that, at the least, the surface layers of PVC-based ISE membranes are extensively hydrated. This study therefore gives further insight into the operation of these membrane-based sensors.