COATED-QUARTZ CRYSTAL RESONATOR (QCR) SENSORS FOR ONLINE DETECTION OFORGANIC CONTAMINANTS IN WATER

Coated-quartz crystal resonators (QCRs) with enhanced surface mass sen sitivity profile are investigated as chemical sensors for the detectio n of volatile organic compounds (VOC) in water. Various polymers that show stability in water and sensitivity to the VOCs are used as coatin g materials. These include poly(ethyl acrylate) (PEA), poly(epichloroh ydrin) (PECH), and poly(octadecyl methacrylate) (PODMA). The main dete ction mechanism investigated in this study is the mechanical loading c onsidered primarily as mass loading. Under appropriate experimental co nditions (e.g., liquid cell, coating thickness, oscillator circuit), l ower detection limits for VOCs can be achieved using QCRs, provided th at noise in the sensor signal is minimized. Inherent noise is introduc ed 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 tri chloroethene, respectively. Results also are presented and discussed f or other polymer coatings with different organic compounds. Using resu lts of the mass loading effect (i.e., the measured frequency shifts), the partition coefficients, K-L, of the analyte molecules in the compo site load are discussed in order to analyze the detection process.