Hydrogen Bond Acidic Polymers for Surface Acoustic Wave Vapor Sensors and Arrays Jay W. Grate,* Samuel J. Patrash, and Steven N. Kaganove Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352 Barry M. Wise Eigenvector Research, Inc., P.O. Box 483, Manson, Washington 98831 Four hydrogen bond acidic polymers are examined as sorbent layers on acoustic wave devices for the detection of basic vapors. A polysiloxane polymer with pendant hexafluoro-2 -propanol groups and polymers with hexa- fluorobisphenol groups linked by oligosiloxane spacers yield sensors that respond more rapidly and with greater sensitivity than fluoropolyol, a material used in previous SAW sensor studies. Sensors coated with the new materi- als all reach 90% of full response within 6 s of the first indication of a response. Unsupervised learning tech- niques applied to pattern-normalized sensor array data were used to examine the spread of vapor data in feature space when the array does or does not contain hydrogen bond acidic polymers. The radial distance in degrees between pattern-normalized data points was utilized to obtain quantifiable distances that could be compared as the number and chemical diversity of the polymers in the array were varied. The hydrogen bond acidic polymers significantly increase the distances between basic vapors and nonpolar vapors when included in the array. The use of an acoustic wave device as a chemical vapor sensor typically requires the application of a sorbent material as a thin film on the surface. 1-6 Ideally, this material will strongly and selectively sorb the vapor of interest to provide a sensitive sensor. Thus, the design of such a material should optimize particular interactions with the target vapor. Where a single sensor does not provide adequate selectivity, the use of sensor arrays with pattern recognition is advantageous. 7-25 Compared to a single sensor, an array of sensors collects more chemical information about a sample so that potentially interfering vapors can be distinguished from the analyte or analytes of interest. A sensor array should be designed to include materials collecting chemical information about the full spectrum of potentially interfering vapors, as well as including one or more sensors optimized for the analyte of interest. Thus, a sorbent material for a sensor array may be selected because its sensitivity and selectivity for the vapor of interest helps to differentiate this vapor from other vapors or because the material helps to differentiate other vapors from the target analyte through its sensitivity to other vapor types and properties. 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