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This paper describes an experimental system for simultaneous permeation of a pressurized test gas through different gas permeable membranes and provides a proof of concept for a novel approach for gas identification/fingerprinting for potential construction of electronic noses. The design, construction, and use of a six-channel system which allows simultaneous gas permeation from a single pressurized gas compartment through six different parallel membranes are presented. The permeated gas is accumulated in confined spaces behind the respective membranes. The rate of gas pressure accumulation behind each membrane is recorded and used as a measure of the gas permeation rate through the membrane. The utilized gas permeable membranes include Teflon AF, silicone rubber, track-etch hydrophilic polycarbonate, track-etch hydrophobic polycarbonate, track-etch polyimide, nanoporous anodic aluminum oxide, zeolite ZSM-5, and zeolite NaY. An analogy between the rate of pressure accumulation of the permeating gas behind the membrane and the charging of an electric capacitor in a single series RC circuit is proposed and thoroughly validated. The simultaneous permeation rates through different membranes demonstrated a very promising potential as characteristic fingerprints for 10 test gases, that is, helium, neon, argon, hydrogen, nitrogen, carbon dioxide, methane, ethane, propane, and ethylene, which are selected as representative examples of mono-, di-, tri-, and polyatomic gases and to include some homologous series as well as to allow testing the potential of the proposed system to discriminate between closely related gases such as ethane and ethylene or carbon dioxide and propane which have almost identical molecular masses. Finally, a preliminary investigation of the possibility of applying the developed gas permeation system for semiquantitative analysis of the CO 2 -N 2 binary mixture is also presented.

Biological and biomedical applications of accelerator mass spectrometry (AMS) use isotope ratio mass spectrometry to quantify minute amounts of long-lived radioisotopes such as (14)C. AMS target preparation involves first the oxidation of carbon (in sample of interest) to CO 2 and second the reduction of CO 2 to filamentous, fluffy, fuzzy, or firm graphite-like substances that coat a -400-mesh spherical iron powder (-400MSIP) catalyst. Until now, the quality of AMS targets has been variable; consequently, they often failed to produce robust ion currents that are required for reliable, accurate, precise, and high-throughput AMS for biological/biomedical applications. Therefore, we described our optimized method for reduction of CO 2 to high-quality uniform AMS targets whose morphology we visualized using scanning electron microscope pictures. Key features of our optimized method were to reduce CO 2 (from a sample of interest that provided 1 mg of C) using 100 +/- 1.3 mg of Zn dust, 5 +/- 0.4 mg of -400MSIP, and a reduction temperature of 500 degrees C for 3 h. The thermodynamics of our optimized method were more favorable for production of graphite-coated iron powders (GCIP) than those of previous methods. All AMS targets from our optimized method were of 100% GCIP, the graphitization yield exceeded 90%, and delta (13)C was -17.9 +/- 0.3 per thousand. The GCIP reliably produced strong (12)C (-) currents and accurate and precise F m values. The observed F m value for oxalic acid II NIST SRM deviated from its accepted F m value of 1.3407 by only 0.0003 +/- 0.0027 (mean +/- SE, n = 32), limit of detection of (14)C was 0.04 amol, and limit of quantification was 0.07 amol, and a skilled analyst can prepare as many as 270 AMS targets per day. More information on the physical (hardness/color), morphological (SEMs), and structural (FT-IR, Raman, XRD spectra) characteristics of our AMS targets that determine accurate, precise, and high-hroughput AMS measurement are in the companion paper.

This paper describes the development and evaluation of instrumentation for the breath-by-breath determination of oxygen and carbon dioxide in respiratory gases. The method is based on nondispersive absorption and uses the 145-nm absorption band for detection of oxygen and the 4.3-micron band for detection of carbon dioxide. A xenon discharge lamp with a sharp band at 147 nm was chosen as the source for the determination of oxygen, and a carbon dioxide discharge lamp with a sharp band at 4.3 micron was chosen for determination of carbon dioxide. A vacuum photodiode was used as the detector for oxygen, and a photoconductive cell with a built-in interference filter was used for detection of carbon dioxide. Plots of absorbance (A) vs concentration (C, %) were linear for oxygen and were nonlinear for carbon dioxide. Typical least-squares calibration equations were A = 0.020C + 0.02 for oxygen (0-100%) and A = 0.0012C2 + 0.050C + 0.008 for carbon dioxide (0-8%). Comparisons of computed (y) vs prepared (x) values for the concentrations given above were linear for both gases, yielding y = (1.00 +/- 0.01)x - 0.13 +/- 0.73 for oxygen and y = (1.07 +/- 0.02)x - 0.04 +/- 0.06 for carbon dioxide. The standard deviations were 1.2% at 50% oxygen and 1.5% at 4% carbon dioxide. Records are presented to illustrate breath-by-breath monitoring of these gases in a healthy subject.

This paper describes calibration strategies in laboratory conditions that can be applied to ensure accurate measurements of the isotopic composition of the CO2 in ultradry air, expressed as d13C and d18O on the VPDB scale, with either FT-IR (in this case a Vertex 70 V (Bruker)) or an isotope ratio infrared spectrometer (IRIS) (in this case a Delta Ray (Thermo Fisher Scientific)). In the case of FT-IR a novel methodology using only two standards of CO2 in air with different mole fractions but identical isotopic composition was demonstrated to be highly accurate for measurements of d13C and d18O with standard uncertainties of 0.09% and 1.03%, respectively, at a nominal CO2 mole fraction of 400 µmol mol-1 in air. In the case of the IRIS system, we demonstrate that the use of two standards of CO2 in air of known but differing d13C and d18O isotopic composition allows standard uncertainties of 0.18% and 0.48% to be achieved for d13C and d18O measurements, respectively. The calibration strategies were validated using a set of five traceable primary reference gas mixtures. These standards, produced with whole air or synthetic air covered the mole fraction range of (378-420) µmol mol-1 and were prepared and/or value assigned either by the National Institute of Standards and Technology (NIST) or the National Physical Laboratory (NPL). The standards were prepared using pure CO2 obtained from different sources, namely, combustion; Northern Continental and Southern Oceanic Air and a gas well source, with d13C values ranging between -35% and -1%. The isotopic composition of all standards was value assigned at the Max Planck Institute for Biogeochemistry Jena (MPI-Jena). [ABSTRACT FROM AUTHOR]

This paper demonstrated an in situ headspace gas chromatography (GC) technique for monitoring bacterial growth using a commercial GC system with a multiple headspace extraction (sampling) mode. The technique was based on measuring the carbon dioxide mass in the headspace of a closed sample vial during the bacteria growth. A mathematic equation was derived in order to calculate the integrated amount of carbon dioxide produced by bacterial growth during the incubation. The method can be used to monitor the bacterial growth rate in a given cultural medium. The present method is very simple, sensitive, and safe. [ABSTRACT FROM AUTHOR]

This paper reports on a newly developed mobile mass spectrometer for comprehensive on-line analysis of complex gas mixtures such as ambient air or industrial process gases. Three ionization methods, namely, the resonance-enhanced multiphoton ionization (REMPI), vacuum-ultraviolet single-photon ionization (SPI), and electron impact ionization (El) are implemented in this instrument and can be operated (quasi-) simultaneously. By means of this setup, a wide range of compounds can be analyzed due to the unique ionization selectivitly and sensitivity profiles provided by the different ionization techniques. The mass spectrometer is designed for field application even under severe conditions. The HEMP! technique is suitable for the selective and soft ionization (without fragmentation) of aromatic compounds at Irace level (ppbv/pptv). The also soft but less selective SPI technique with 1 18-nm vacuum-ultraviolet laser pulses is used as a second laser-based ionization method. Mass spectra obtained by this technique show profiles of most organic compounds (aliphatic and aromatic species) and of some low II? inorganic substances (e.g., ammonia, nitrogen oxide) down to ppbv concentrations. In addition to the laser-based ionization techniques, El ionization can be used for analysis of the bulk components such as water, oxygen, nitrogen, and carbon dioxide as well as for detection of inorganic minor components such as HCN or HC1 from combustion flue gases at ppmv concentration levels. Each method yields specific mass spectrometric information of the sample composition. Special techniques have been developed to combine the three lonization methods in a single mass spectrometer and to allow the quasi-parallel application of all three ionization techniques. [ABSTRACT FROM AUTHOR]