Coated-quartz crystal resonator (QCR) sensors for on-line detection of organic contaminants in water

Coated-quartz crystal resonators (QCRs) with enhanced surface mass sensitivity profile are investigated as chemical sensors for the detection of volatile organic compounds (VOC) in water. Various polymers that show stability in water and sensitivity to the VOCs are used as coating materials. These include poly(ethyl acrylate) (PEA), poly(epichlorohydrin) (PECH), and poly(octadecyl methacrylate) (PODMA). The main detection mechanism investigated in this study is the mechanical loading considered primarily as mass loading. Under appropriate experimental conditions (e.g., liquid cell, coating thickness, oscillator circuit), lower detection limits for VOCs can be achieved using QCRs, provided that noise in the sensor signal is minimized. Inherent noise is introduced by the decrease in the crystal Q, the parasitic elements within the oscillator circuit, and the liquid flow on the crystal surface. Using PEA-coated QCRs operating at the series-resonant frequency, detection limits of 150 ppb and 500 ppb are found for tetrachloroethane and trichloroethene, respectively. Results also are presented and discussed for other polymer coatings with different organic compounds, Using results of the mass loading effect (i.e., the measured frequency shifts), the partition coefficients, K/sub L/, of the analyte molecules in the composite load are discussed in order to analyze the detection process.