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Vapor

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Jay W Grate - One of the best experts on this subject based on the ideXlab platform.

  • single walled carbon nanotube paper as a sorbent for organic Vapor preconcentration
    Analytical Chemistry, 2006
    Co-Authors: Feng Zheng, David L Baldwin, Leonard S Fifield, Norman C Anheier, Christopher L Aardahl, Jay W Grate
    Abstract:

    Single-walled carbon nanotubes were examined as an adsorptive material for a thermally desorbed preconcentrator for organic Vapors. The nanotubes were processed into a paper form and packed into a metal tube for flow-through sampling. Adsorbed Vapors were released by a temperature-programmed desorption method and detected downstream with a flexural plate wave Vapor sensor. The tested Vapors, methyl ethyl ketone, toluene, and dimethyl methylphosphonate, were released from the packed column at different temperatures. The Vapors were retained more strongly than previously observed for the widely used Tenax porous polymer, indicating a significant affinity of the single walled nanotubes for organic Vapors.

  • method for unknown Vapor characterization and classification using a multivariate sorption detector initial derivation and modeling based on polymer coated acoustic wave sensor arrays and linear solvation energy relationships
    Analytical Chemistry, 1999
    Co-Authors: Jay W Grate, Barry M Wise, Michael H. Abraham
    Abstract:

    A novel method for the characterization and classification of unknown Vapors based on the response on an array of polymer-coated acoustic wave Vapor sensors is presented. Unlike existing classification algorithms, the method does not require that the system be trained on all samples to be identified. Instead, the solvation parameters of the unknown Vapor are estimated given the sensor responses and the linear solvation energy relationship coefficients of the sorbent polymer coatings. The Vapors can then be identified from a database of candidate Vapor parameters. The method is implemented in a way that is analogous to multivariate calibration with classical least squares, where the individual Vapor parameters are treated as pure compounds. It is not necessary to know the Vapor concentration of the Vapor to perform the classification. In principle, it is possible to estimate the concentration of an unknown Vapor for which the system has not been trained or calibrated. It is also possible to implement the m...

  • smart sensor system for trace organophosphorus and organosulfur Vapor detection employing a temperature controlled array of surface acoustic wave sensors automated sample preconcentration and pattern recognition
    Analytical Chemistry, 1993
    Co-Authors: Jay W Grate, S L Rosepehrsson, M Klusty, David L Venezky, Hank Wohltjen
    Abstract:

    A smart sensor system For the detection of toxic organophosphorus and toxic organosulfur Vapors at trace concentrations has been designed, fabricated, and tested against a wide variety of Vapor challenges. The key features of the system are an array of four surface acoustic wave (SAW) Vapor sensors, temperature control of the Vapor sensors, the use of pattern recognition to analyze the sensor data, and an automated sampling system including thermally desorbed preconcentrator tubes (PCTs). All the electronics necessary to control and operate the various subsystems and to collect and process the data are included in the system

Hank Wohltjen - One of the best experts on this subject based on the ideXlab platform.

G C Frye - One of the best experts on this subject based on the ideXlab platform.

  • analyzing organic Vapors in exhaled breath using a surface acoustic wave sensor array with preconcentration selection and characterization of the preconcentrator adsorbent
    Analytica Chimica Acta, 1998
    Co-Authors: William A Groves, Edward T. Zellers, G C Frye
    Abstract:

    Abstract 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 8 mm of Hg (m-xylene) to 420 mm 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 200 ppm was demonstrated.

Edward T. Zellers - One of the best experts on this subject based on the ideXlab platform.

  • Personal monitoring instrument for the selective measurement of multiple organic Vapors.
    American Industrial Hygiene Association Journal, 2000
    Co-Authors: Jeongim Park, Guo Zheng Zhang, Edward T. Zellers
    Abstract:

    Development and laboratory testing of a small instrument capable of recognizing and quantifying multiple organic Vapors at low- and sub-ppm concentrations is described. The instrument is slightly larger than a standard personal sampling pump and employs an array of three polymer-coated surface-acoustic-wave microsensors for Vapor detection. Vapors are first trapped on a miniature adsorbent preconcentrator housed within the instrument and then thermally desorbed for analysis by the microsensor array. Each measurement cycle requires 5.5 min. The collective responses from the array are stored and then analyzed using pattern recognition methods to yield the identities and concentrations of collected Vapors and Vapor mixture components. Following initial optimization of instrument operating parameters, calibrations were performed with 16 organic solvent Vapors and selected mixtures to establish a response library for each of two identical instruments. Limits of detection ≤0.1 × threshold limit value were obtai...

  • Vapor recognition with an integrated array of polymer coated flexural plate wave sensors
    Sensors and Actuators B-chemical, 2000
    Co-Authors: Jeongim Park, Dylan Heldsinger, Meng Da Hsieh, Edward T. Zellers
    Abstract:

    Abstract Preliminary testing of a prototype instrument employing an integrated array of six polymer-coated flexural plate wave (FPW) sensors and an adsorbent preconcentrator is described. Responses to thermally desorbed samples of individual organic solvent Vapors and binary and ternary Vapor mixtures are linear with concentration, and mixture responses are equivalent to the sums of the responses of the component Vapors, which co-elute from the preconcentrator in most cases. Limits of detection as low as 0.3 ppm are achieved from a 60-s (34 cm 3 ) air sample and peak widths at half-maximum range from 1 to 4 s. Tests at different flow rates suggest that the kinetics of Vapor sorption in the sensor coating films may limit responses at higher flow rates, however, low data acquisition rates may also be contributory. Assessments of array performance using independent test data and Monte Carlo simulations with pattern recognition indicate that individual Vapors and certain binary and ternary mixtures can be recognized/discriminated with very low error. More complex mixtures, and those containing homologous Vapors, are problematic. This is the first report demonstrating multi-Vapor analysis with an integrated FPW sensor array.

  • analyzing organic Vapors in exhaled breath using a surface acoustic wave sensor array with preconcentration selection and characterization of the preconcentrator adsorbent
    Analytica Chimica Acta, 1998
    Co-Authors: William A Groves, Edward T. Zellers, G C Frye
    Abstract:

    Abstract 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 8 mm of Hg (m-xylene) to 420 mm 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 200 ppm was demonstrated.

Xudong Fan - One of the best experts on this subject based on the ideXlab platform.

  • self referenced composite fabry perot cavity Vapor sensors
    Optics Express, 2012
    Co-Authors: Karthik Reddy, Xudong Fan
    Abstract:

    We develop a versatile, self-referenced composite Fabry-Perot (FP) sensor and the corresponding detection scheme for rapid and precise measurement of Vapors. The composite FP Vapor sensor is formed by etching two juxtaposed micron-deep wells, with a precisely controlled offset in depth, on a silicon wafer. The wells are then coated with a Vapor sensitive polymer and the reflected light from each well is detected by a CMOS imager. Due to its self-referenced nature, the composite FP sensor is able to extract the change in thickness and refractive index of the polymer layer upon exposure to analyte Vapors, thus allowing for accurate Vapor quantitation regardless of the polymer thickness, refractive index, and light incident angle and wavelength. Theoretical analysis is first performed to elucidate the underlying detection principle, followed by experimental demonstration at two different incident angles showing rapid and consistent measurement of the polymer changes when the polymer is exposed to three different analytes at various concentrations. The Vapor detection limit is found to be on the order of a few pico-grams (~100 ppb)

  • on chip fabry perot interferometric sensors for micro gas chromatography detection
    Sensors and Actuators B-chemical, 2011
    Co-Authors: Karthik Reddy, Yunbo Guo, Jing Liu, Wonsuk Lee, Maung Kyaw Khaing Oo, Xudong Fan
    Abstract:

    Abstract We fabricated and characterized on-chip Fabry–Perot (FP) Vapor sensors for the development of on-column micro-gas chromatography (μGC) detectors. The FP sensors were made by coating a thin layer of polymer on a silicon wafer. The air–polymer and polymer–silicon interfaces form an FP cavity, whose resonance wavelengths change in response to the Vapor absorption/desorption, thus allowing for rapid detection and quantification of Vapors. For proof-of-concept, two polymers (PDMS and SU-8) were used independently and placed in an array in a microfluidic channel, and showed different sensitivities for different Vapors. A sub-nano-gram detection limit and sub-second response time were achieved, representing orders of magnitude improvement over those previously reported. This on-chip design will enable the unprecedented integration of optical Vapor sensors with μGC systems.