Dennis Stein Everhart

AC-impedance-based chemical sensors for organic solvent vapors

Abstract A type of chemical sensor based on impedance spectroscopy (IS) measurements utilizing an interdigital transducer structure on a glass substrate is investigated for the detection of organic solvent molecules, such as chloronated hydrocarbons, in the gas phase. The IDT structures were coated with sensitive material such as soluble tetrakis-t-butyl phthalocyaninatonickel(II), ethylcellulose, poly(ethyl acrylate), and poly(etherurethane). The target organic solvent molecules are dichloromethane, chloroform, trichloroethene, tetrachloroethene, toluene, and ethanol. The sensor responses were monitored by measuring changes in the transducer/coating composite properties upon exposure to the organic solvent molecules. The sensor parameters of interest include the electrostatic capacitance, the resistance of the composite and the relaxation time, which will lead to the implementation of a multi-information sensor. Results are presented and compared for selected samples with completely reversible sensor signals at room temperature. Based on the measurements, use of metal complexes can improve sensitivity and increase the signal-to-noise ratio.

Polymer-coated QCR sensors for the detection of organic solvents in water

Abstract Poly(ethyl acrylate) (PEA), poly(epichlorohydrin) (PECH) and a silicon-based copolymer of trimethoxypropylsilane/octadecyltrimethoxysilane (TMPS/ODTMS) were used as sensitive materials for the detection of organic solvent molecules in water. Quartz crystal resonators (QCR) with modified electrode configurations are used to monitor the changes in mass and in electrical properties by measuring the shifts in series resonance frequency ( f s ), parallel resonance frequency ( f p ), and frequency of maximum admittance ( f m ), respectively. The result is a multi-information chemical sensor. The sensor signals are completely reversible at room temperature with the response and recovery time in the order of minutes under our measurement conditions. The sensitivities obtained from the measurements of f m for all organic solvents investigated are generally larger than those obtained from f s and f p . It is also found that there is no correlation between the measured sensitivities of the series resonance frequency and the boiling point temperatures of the organic solvents investigated in the liquid phase under our experimental conditions, as is generally obtained in the gas phase.