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23 November 1999 Characterization of polymer-coated QCRs in the detection of organic compounds in liquid environments
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The design of sensor arrays using polymer-coated QCRs for the practical detection of organic compounds in aqueous environments requires the appropriate selection of sensitive coatings. This selection of the coatings is performed through a study of the sorption processing terms of the partition coefficients of the analytes in the coatings. However, the determination of the partition coefficients in only accurate if all contributions to the total measured frequency shifts, (Delta) fs can be accounted for. While mass loading is often assumed to be the dominant factor used in determining partition coefficients, viscoelastic effect may also contribute to changes in (Delta) fs, especially in liquid environments. Both the effect of viscoelastic properties and the effect of the mass loading on the sensor responses are investigated by using a network analyzer and oscillator circuits. Different types of coatings including rubbery and glassy polymers are investigated, and the targeted analytes include classes of polar compounds, nonpolar compounds and chlorinated hydrocarbons. It is shown that changes in viscoelastic properties during and after analyte sorption can be significant enough to place the sensor in the non-gravimetric regime. However, for most applications invovling relatively low concentrations of organic compounds, the subsequent change in viscoelastic properties are still such that the sensors operate in the linear regime. In that case, the measured (Delta) fs, hence the calculated partition coefficients can still be used for an approximate classification and selection of the coatings.
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Fabien J. Josse, Rongnong Zhou, Rupa Patel, Kristofer Zinszer, and Richard W. Cernosek "Characterization of polymer-coated QCRs in the detection of organic compounds in liquid environments", Proc. SPIE 3856, Internal Standardization and Calibration Architectures for Chemical Sensors, (23 November 1999);

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