Design and Implementation of QCM Virtual Sensing Schemes for Analyses of Volatile Organic Compounds

Abstract

Sensor arrays have evolved as powerful approaches for providing detection and discrimination of volatile organic compounds (VOCs) as required across numerous analytical applications. Such systems typically comprise a number of cross reactive sensor elements, which generate analyte specific response patterns upon exposure to VOCs, and are known as multisensor arrays. When evaluated using statistical methods, these response patterns facilitate classification of VOCs. As an alternative, a single dynamically operated sensor could also be used to generate analyte specific response patterns. This approach is known as a virtual sensor array (VSA) and can exhibit significant advantages when compared to MSAs. Some advantages include lower power consumption, sensor drift, material cost, and experimental preparatory time. Furthermore, several dynamically operated sensors could be used in tandem (using the MSA and VSA scheme in a complementary fashion) to fabricate virtual multisensor arrays (V-MSAs). Such systems would exhibit greater data density than either the MSA or VSA, and are promising for samples that are particularly challenging to discriminate. Among the various systems utilized for VOC discrimination, sorption based systems hold considerable promise because they are simple and inexpensive yet highly effective. This dissertation is focused on the development of array sensing schemes using ionic liquids (ILs), a group of uniform materials based on organic salts (GUMBOS), and binary blends of either IL or GUMBOS with polymer as recognition elements and the quartz crystal microbalance (QCM) as the transducer. Towards this end, ILs, which are defined as organic salts with melting points below 100 °C, and group of uniform materials based on organic salts (GUMBOS) which extend the melting range of ILs to 250 °C to encompass similar solid phase salts, were used to design the first examples of QCM based VSAs, and V-MSAs, for pure VOC and complex mixture analyses. Furthermore binary blends of organic salts and polymer were used to fabricate the first VSA with the capability to identify and approximate molecular weight of pure VOCs. By and large, the studies presented here demonstrate the excellent potential of these materials and techniques for advancement of vapor phase measurement science.