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Measurement of breath NH3 is of interest in clinical applications as it can be used as a measure of kidney/liver functions as well as halitosis. We have developed a liquid-film conductivity sensor to measure NH3 in human breath. A film of dilute H2SO4 is formed on the top of two metal capillary tubes placed in a concentric annular arrangement. The tube exterior has been specially treated to render it hydrophilic. As breath passes over the sensor tip, the film collects NH3 and the solution conductivity (measured by the concentric capillaries functioning as electrodes) decreases accordingly. This initial rate of conductivity decrease was determined to be the best metric (most rapid and least dependent on breath pCO2) for ammonia, relative to time to attain complete neutralization (conductivity minimum) or the final rate of conductivity increase as more ammonia dissolves after neutralization. The absorbing solution composition was optimized so that CO2 does not interfere. Both dynamic measurement using mask sampling and offline balloon sampling were performed. Ammonia readily absorbs on surfaces when significant concentrations of water vapor are present. As such, memory effects are common when analyzing human breath for ammonia. This problem was successfully eliminated. The results from this sensor agreed well with data obtained by a solution-phase fluorometric technique using a porous membrane diffusion scrubber and o-phthalaldehyde derivatization chemistry. For breath CO2 measurement, the applicability of a similar sensor that relies on a NaOH film was also demonstrated.

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The association constants of ferrocene with cyclodextrins (CyD’s) in an aqueous medium at 25 °C have been determined by solubility measurements of ferrocene in both the absence and presence of CyD. The solubility of ferrocene in pure water was found to be (4.25 ± 0.02) × 10−5 mol dm−3 at 25.0 ± 0.1 °C. The β- and γ-CyD’s form only 1 : 1 complexes with ferrocene. The 1 : 1 association constants were determined to be (1.39 ± 0.21) × 102 (α), (1.65 ± 0.04) × 104 (β), and (9.04 ± 0.11) × 102 dm3 mol−1 (γ). The 2 : 1 (CyD : ferrocene) association constant was (2.36 ± 0.06) × 103 dm3 mol−1 (α). Ferrocene-included CyD precipitates were also prepared in water, and their stability upon drying in air was studied. The sublimation enthalpy of ferrocene in the temperature range of 290.65 to 298.15 K was estimated to be 74.2 ± 1.5 kJ mol−1.

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A honeycomb structure microchannel scrubber was developed to achieve efficient and stable gas collection. A thin porous membrane was pasted on a microchannel by the adhesive force of a fresh polydimethylsiloxane surface. The microchannel scrubber achieved much more efficient gas collection than conventional impingers and diffusion scrubbers. Two sets of the microchannel scrubbers and detectors were integrated in a 10 cm x 9 cm plastic board to create a micro gas analysis system (microGAS) for simultaneous measurements of H2S and SO2. The whole system including a battery was incorporated in a carrying case 34 cm W x 16 cm D x 17 cm H for use in the field. Liquid flows at 30 microl min(-1) were obtained by bimetal micropumps. The estimated detection limits were 0.1 ppbv for H2S and 1 ppbv for SO2. The system was demonstrated for real atmospheric gas analysis, and the results agreed well with data concurrently obtained by ion chromatography coupled with a cylindrical diffusion scrubber. The system we developed allowed automated continuous analyses in the field and achieved a much higher time resolution compared to those by ion chromatographic analysis.