High-Performance Gas Sensing of CO: Comparative Tests for Semiconducting (SnO(2)-Based) and for Amperometric Gas Sensors.

A comparison of the stability and sensitivity for two different sensor types (semiconductor SnO(2) devices, amperometric electrochemical sensors) has been performed. Sensitivities and drifts in the signal and in the background for various concentrations of CO have been studied for thick-film SnO(2) sensors (Pt and Pd doped) for a period in excess of 8 months. Similar performance data have been recorded for commercial amperometric sensors for a period in excess of 4 years. The two different sensor types investigated here were also compared to the well-known commercial Figaro TGS 822 sensor at similar concentrations. An objective approach for comparing different types of sensors has been developed using the "analytical sensitivity".

Impedance based sensing of the specific binding reaction between Staphylococcus enterotoxin B and its antibody on an ultra-thin platinum film.

Immunobiosensing techniques to measure specific antigen-antibody binding reactions are important in the development of biosensor applications in biotechnology, in vitro diagnosis, medicine and food technology. An immunobiosensor was constructed to measure the specific binding reaction between Staphylococcus enterotoxin B (SEB) and anti-SEB antibodies. The biosensor comprised an anti-SEB bioactive layer covalently immobilized on an ultra-thin platinum (Pt) film sputtered onto a 100 nm thick silicon dioxide layer on a silicon chip. The Pt film was discontinuous with a normal thickness of 25 A. The impedance of the Pt film decreased during the binding of the anti-SEB to SEB in phosphate buffered saline (PBS) at room temperature. The impedance decreases were irreversible in PBS before saturation of the specific binding sites. When saturated, the impedance at 100 Hz was 14% of the value obtained for the fresh anti-SEB layer in PBS. The magnitude of the impedance (Z) decrease followed a simple relationship with SEB concentration in the range between 0.389 and 10.70 ng/ml SEB. The specificity of the biosensor was demonstrated by showing that no irreversible impedance decreases occurred when the sensor was exposed to 100 ng/ml kappa-casein, or alpha-lactalbumin, in PBS.

Preliminary evaluation of an active end-of-service-life indicator for organic vapor cartridge respirators.

Data are presented on a microwatt chemiresistor microsensor for use with negative-pressure organic vapor respirators. This sensor would operate at or within a sorbent bed and detect parts per million levels of chemical vapors and/or gases as a function of sensor resistance. Sensors were evaluated against four challenge concentrations of ethyl acetate (750 ppm, 1000 ppm, 1500 ppm, and 2000 ppm). Direct comparison of breakthrough times and curves for the chemiresistor microsensor and a standard infrared (IR) detector system were made. The chemiresistor sensor responses were found to correlate well with the IR system. The evaluation showed that although the chemiresistor sensors were not as sensitive as the IR detectors, they could be used if located inside the charcoal bed. Thus, these sensors could function as organic-vapor detectors and could be used in cartridge applications. However, further improvements in stability and sensitivity of these chemiresistor sensors is necessary.

An optical waveguide acid vapor sensor.

An optical waveguide sensor for the detection of acid vapors is described. The chemically sensitive reagent coating consists of bromothymol blue indicator suspended in a Nafion polymer film. The sensor uses a 562 nm LED source and a phototransistor detector. Response to hydrochloric acid and hydrogen sulphide vapours is both rapid and reversible, with an estimated detection limit for hydrogen sulphide of less than 15 ppm. The sensors exhibits generalized response to protonic acid vapours, but does not produce an indicator response to carbon dioxide, even at large concentrations (1100 mg/l.) in the presence of water vapor. The sensor exhibits a systematic interference from water vapor which may be corrected by a different approach, either using a reference sensor (Nafion/no indicator) or by monitoring sensor response at two wavelengths.

Portable instrumentation for on - site analysis of toxic vapors

The center for Environmental Research at Argonne National Laboratory has developed a versatile toxic vapor analyzer. This instrument, the chemical Parameter Spectrometer (CPS-100), was designed to detect, identify, and monitor any one of 26 - compounds strored in the library, which itself may be update or expanded (perhaps to >50 compounds). Implementation of such an algorithm would effectively expanded the library size and would still provide the user with sufficient data (perhaps class identification of compounds) so as to assess many potential hazards on the spot.The reliability of such a algorithm for "hazard classification" has been evaluated and compared to the present algorithms which selectively identify unknow vapors.(AU)

Characterization of airborne trace metal and trace organic species from coal gasification.

Fugitive emissions from a slagging fixed-bed coal-gasification pilot plant were analyzed by flameless atomic absorption spectrophotometry, gas chromatography, and mass spectrometry for trace metal and trace organic species. Analysis of the size distributions of airborne particulate matter inside the plant showed an abundance of large metal-containing particles; outdoor distributions in the vicinity of the plant resembled the indoor distributions, suggesting the importance of the gasifier in influencing ambient air quality. This conclusion was further supported by identification of similar organic compounds inside and outside the plant. Trace element enrichment factors based on the earth's crustal composition were greater than those based on the composition of the lignite used in the gasifier, showing the importance of characterizing the proper source material when inverstigating chemical fraction during aerosol formation. Enrichments in the present study were much greater than those found in previous sampling during aborted start-up and cleaning procedures, where normal operating temperatures had not yet been reached. Both studies showed evidence of enrichment factors which decreased with increasing particle size. Although much of the airborne mass was associated with large particles having low respirability, the high concentrations of some metals indoors suggests that further assessment of potential occupational exposures is warranted.

Characterization of airborne particles at a high-btu coal-gasification pilot plant.

Airborne particles in fugitive emissions have been measured at a slagging fixed-bed coal-gasification pilot plant using lignite. Sampling was conducted during shutdown operations and opening of the gasifier following an aborted startup. Aerosol collected with a Sierra high-volume impactor was subjected to analysis by gas chromatography, mass spectrometry, and scanning electron microscopy; aerosol collected with an Andersen low-volume impactor was subjected to flameless atomic absorption analysis. The data show that the bulk of the trace organic material is associated with small particles: these data are similar to data on ambient air reported in the literature. Particle morphologies resemble those of fly ash from coal combustion, including smooth spheres, vesicular spheres, and crystalline material. Trace element size distributions are bimodal and resemble data for ambient air. Pb-containing particles are generally submicron, while particles containing Al, Fe, and other crustal species are mostly of supermicron size. Aluminum-based aerosol enrichment factors calculated from the lignite composition show that the composition of the aerosol resembles that of the coal, with the exception of modest enrichments of Mg, Na, As, and Pb in the submicron size range. Aerosol enrichment factors based on the earth's crustal composition are somewhat greater than those based on coal composition for several elements, suggesting potential errors in using crustal enrichment data to investigate chemical fractionation during aerosol formation.

Instrumental carbon monoxide dosimetry.

Modern technology for the ambient monitoring of carbon monoxide has been developed to produce a portable electrochemical instrument capable of the personal exposure to carbon monoxide. The performance characteristics of this device have been studied so that the unambiguous interpretation of field data could be performed. A study of the carbon monoxide exposure in a light manufacturing facility illustrate that effective dosimetry can be performed with expectations of accuracy typically better than +/- 15%, and that voluntary carbon monoxide exposures such as smoking were a significant contribution to the individual's exposure. Significant definition of the carbon monoxide exposure profile can be achieved with an instrument approach to the collection of the dosimetric data.

Electrochemical determination of hydrazine and methyl- and 1,1-dimethylhydrazine in air.

An electrochemical cell capable of detecting levels of hydrazine, methylhydrazine (MMH) and 1,1-dimethylhydrazine (UDMH) in air is described. It is coupled with a dynamic air-sampling system and electronic control and amplification circuitry to provide a direct-reading portable analyser. The characteristics of this monitoring instrument are discussed. While most of the reported data are specifically for MMH vapour analysis, qualitatively similar results can be obtained when using this instrument for hydrazine or UDMH measurements.

Electrochemical gas chromatographic detection of hydrogen sulfide at PPM and PPB levels.

An electrochemical detector for gas chromatographic analysis of hydrogen sulfide is described and its operating characteristics are discussed. The detector operation is based upon the measurement of the current when hydrogen sulfide is electrochemically oxidized at a diffusion electrode. The lower detectable limit was 3 X 10(-12) grams H2S, the precision was 0.5% and analysis was achieved within 2 minutes. Accuracy was limited principally by the preparation of calibration samples and the availability of standard reference gas mixtures.