3,164,004 1/1965 King, Jr. ................................. 73/23 3,89.4:3 6/1975 Sievers et al. ......... ... S5/386 X 4,029,583 6/1977 HoChang et al. ................ 55/386 X 4,140,653 2/1979 Inura et al. ...................... 55/386 X 4,277,322 7/1981 Kane ................................ 204/95 S 4,335,017 6/1982 Miles et al. ......................, 55/386 X 4,348,296 9/982 Bauman et al. ..., ... 55/386 X 4,348,297 9/1982 Bauman et al. .... ... 55/386 X 4,504,522 3/1985 Kaiser et al. ........................ 427/103 4,520,122 5/1985 Arena ............. ... 55A386 X 4,652,280 3/1987 Boeren et al. . ... 55A386 X 4,782,040 l/1988 Revis et al. ........ ... 55A386 X 4,834,496 5/1989 Blyler, Jr. et al. . ... 350/96.29 4,847,594 7/1989 Stetter ................ ...... 350/540 4.950,634 8/1990 Wiians et al. ... ... 55/386 X 4,950,635 8/1990 Williams et al. ... ... SSA386 X

A portable SAW sensor array instrument with integrated chemometric software has been developed to identify a variety of chemical classes like paraffinics, aromatics, chlorinated hydrocarbons, ketones and alcohols. The system was trained with known chemicals and a chemometric model was developed for two applications: bulk VOC identification and environmental monitoring of trace level VOCs. The instrument was then successfully tested in the lab and in the field for these two applications. The ability to identify and quantify these VOCs over a dynamic range from low ppm trace levels to high concentrations (close to the chemical's vapor pressure) was demonstrated.

The analysis of organic vapors in exhaled breath can provide information about chemical exposures and health status. This article describes work aimed at developing a small prototype instrument that employs an array of four polymer-coated surface acoustic wave (SAW) sensors and a thermally desorbable adsorbent preconcentrator for rapid breath analysis. The adsorbent used in the preconcentrator is critical to achieving adequate sensitivity and compensating for the high background of water vapor. Eight granular adsorbents packed into narrow bore glass tubes wrapped with NiCr wire were evaluated individually and in selected dual-bed configurations with respect to the pressure drop of the packed bed, retention of water vapor, and adsorption/desorption efficiency of each of several organic solvent vapors. Although adsorbents of Tenax GR® and Carbotrap® performed well, a highly porous styrene-divinylbenzene resin demonstrated superior overall performance and was selected for further testing. Solvents ranging in vapor pressure from 8mm of Hg (m-xylene) to 420mm of Hg (dichloromethane) were efficiently trapped from 0.25-l spiked breath samples and efficiently desorbed at 170°C. Incorporating an intermediate dry-air purge step prior to thermal desorption of samples selectively removed co-adsorbed water and reduced the limits of detection (LOD) by an order of magnitude. Results of detailed breakthrough studies were considered in the context of the modified Wheeler and Langmuir adsorption models and used to determine the minimum quantity of adsorbent required to prevent saturation of the adsorbent bed for each test vapor. Measurement of vapors at concentrations ranging from sub-ppm to 200ppm was demonstrated.

The analysis of organic vapors in exhaled breath can provide information about chemical exposures or medical abnormalities. This paper describes work toward development of a prototype instrument employing an array of four polymer-coated SAW sensors and an adsorbent preconcentrator for rapid breath analysis. The adsorbent used in the preconcentrator is a critical system component. Test results led to the selection of a highly porous styrene-divinylbenzene resin from among other candidate adsorbent materials on the basis of its high vapor adsorption capacity, low pressure drop, and low water vapor retention. Limits of detection well below accepted exposure standards were achieved in 250-ml spiked breath samples for all of the 16 vapors tested. Response patterns permitted reliable discrimination and identification of ail individual vapors and many vapor mixtures. Predictive performance models were used to determine the nature and frequency of expected errors in vapor identification.

This report summarizes the results of a Laboratory Directed Research and Development (LDRD) effort to study and model surface acoustic wave (SAW) devices for environmental applications. The response of polymer-coated SAW devices to temperature changes and polymer vapor absorption is examined. A perturbational approach is used to relate velocity and attenuation responses to film translational and strain modes generated by the SAW. Two distinct regimes of film behavior arise, causing different SAW responses. For glassy films, displacement is nearly uniform across the film thickness, varying only in the direction of propagation. A model developed to predict velocity and attenuation in this regime, reduces to the familiar Tiersten (Wohltjen) equation for purely elastic films. For elastomeric (rubbery) films, inertial effects cause a phase lag to occur across the film for shear displacements. A model to account for these cross-film displacement gradients predicts a characteristic resonant response when the film phase shift reaches np/2, where n is an odd integer. These model predictions are compared with measured responses from polyisobutylene-coated SAW devices as temperature is varied and during exposure to high vapor concentrations.

Sensors UpdateVolume 2, Issue 1 p. 37-83 Sensor Technology Acoustic Wave Sensors Jay W. Grate, Jay W. Grate Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352Search for more papers by this authorGregory C. Frye, Gregory C. Frye Microsensor Research and Development Dept., Sandia National Laboratories, Albuquerque, NM 87185Search for more papers by this author Jay W. Grate, Jay W. Grate Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352Search for more papers by this authorGregory C. Frye, Gregory C. Frye Microsensor Research and Development Dept., Sandia National Laboratories, Albuquerque, NM 87185Search for more papers by this author First published: October 1996 https://doi.org/10.1002/1616-8984(199610)2:1<37::AID-SEUP37>3.0.CO;2-FCitations: 40AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume2, Issue1October 1996Pages 37-83 RelatedInformation

Jet fuel is used as a coolant in the aviation fuel system and thermal loads on fuel are anticipated to increase concurrently with the performance of advanced aircraft. Hydrocarbon-based fuel form deposits at high temperatures, reducing heat exchanger efficiencies and obstructing values, filters and nozzles. Real-time monitoring of degradation product deposition from thermally-stressed jet fuels is possible using a QCM. Deposition rates of Amgstroms par minute are easily measurable

On-line chemical monitoring systems can help ensure safe, environmentally sound operation of industrial processes using hazardous chemicals. Using polymer-coated surface acoustic wave (SAW) sensors, we have demonstrated monitors that are capable of detecting dilute concentrations of volatile organic species. Using changes in both wave velocity and wave attenuation, the identity and concentration of an isolated chemical species can be determined. A polysiloxane coating has been found to provide unique properties for monitoring chlorinated hydrocarbons (CHCs) such as trichloroethylene: good discrimination of CHCs from most other organic species, rapid and reversible sensor response, and low detection limits. Using this technology, a portable acoustic wave sensor (PAWS) system has been constructed. 7 refs., 4 figs.

ABSTRACTWe have investigated the use of porous oxide coatings, formed using sol-gel chemistry routes, as the discriminating elements of acoustic wave (AW) chemical sensors. These coatings provide several unique advantages: durability, high adsorption capacity based on large surface areas, and chemical selectivity based on both controlled pore size and acid/base, ion exchange or chelation chemistry. The porosity of these coatings is determined by performing nitrogen adsorption isotherms using the AW device response to mass changes to monitor the uptake of nitrogen at 77 K. These studies demonstrate how sol-gel chemistry and film deposition can be combined to tailor the microstructure of thin oxide coatings. The chemical sensitivity and selectivity obtained with this class of coatings will be demonstrated using several examples: hydrous titanate ion exchange coatings, zeolite/silicate microcomposite coatings, and surface-modified silicate films.

Inert hydrophobic solid particles have been found to exhibit antifoam action for many systems. A mechanism for particle-induced film rupture is proposed, and a hydrodynamic analysis is performed to determine criteria for effective action. A comparison of predictions from the analysis with experimental data indicates that the particle shape, the receding contact angle, qrec, and the adsorption rate for the surfactant solution are the critical parameters.