Gas chromatographic analysis of trace impurities in chlorine trifluoride

The gas chromatographic determination of trace gaseous impurities in highly reactive fluorinated gaseous matrices presents unique requirements to both equipment and techniques. Especially problematic are the gases normally present in ambient air namely oxygen and nitrogen. Analysing these gases at the low microl/l (ppm) level requires special equipment and this publication describes a custom-designed system utilising backflush column switching to protect the columns and detectors. A thermal conductivity detector with nickel filaments was used to determine ppm levels of impurities in ClF3.     

Combined thermogravimetry and fourier transform infrared spectroscopy techniques for gas evolution analysis

The usefulness of thermogravimetry has been amply demonstrated for a wide variety of material analysis applications. In many instances, however, additional information is required for adequate characterization of the sample and its thermal decomposition behaviour. In this respect, the analysis of evolved gases, or condensed liquids, has proven a highly useful approach. Among the various physical methods used for analysis of the thermal degradation products, infrared spectroscopy has often been found very powerful, being versatile, rapid and widely accessible. In this study, we report a simple new approach in which the evolved gases and condensed liquids from the thermal decomposition of various products are recuperated in an infrared gas cell and on a PVC membrane filter, respectively. The gaseous components were analysed by transmission FT-IR, and the condensed liquid products were examined directly on the PVC membrane by FT-IR in the internal reflexion mode. The technique was used, for example, to examine the pyrolysis products (gases and liquid) of Koberit, a proposed substitute for asbestos. The method was also applied to the study of chemically derivatized asbestos materials in an attempt to unravel the surface chemical modifications.     

A new cataluminescence gas sensor based on SiO2 nanotubes fabricated using carbon nanotube templates

In the present work, two morphologies of SiO₂ nanomaterials (SiO₂ nanotubes and nanoparticles) have been successfully synthesized in supercritical fluids (SCFs). The cataluminescence (CTL) features of the two SiO₂ nanomaterials to some common harmful gases were compared, and the results showed that SiO₂ nanotubes had better CTL sensing characteristic to some common harmful gases. The SiO₂ nanotubes not only had uniform size and shape with a high specific surface area, but also exhibited superior sensitivity and selectivity to ethyl acetate vapor. Using the SiO₂ nanotubes as sensing material, a CTL sensor for ethyl acetate vapor was developed. The proposed sensor showed high sensitivity and specificity to ethyl acetate at optimal temperature of 293 °C, a wavelength of 425 nm and a flow rate of 345 mL/min. With a detection limit of 0.85 ppm, the linear range of CTL intensity versus concentrations of ethyl acetate vapor was 2.0-2000 ppm. None or only very low levels of interference were observed while the foreign substances such as acetone, acetaldehyde, acetic acid, formaldehyde, ammonia, ethanol, benzene and methanol were passing through the sensor. This method allows rapid determination of gaseous ethyl acetate at workshop.     

Determination of volatile organic compounds in human breath for Helicobacter pylori detection by SPME-GC/MS

Helicobacter pylori living in the human stomach release volatile organic compounds (VOCs) that can be detected in expired air. The aim of the study was the application of breath analysis for bacteria detection. It was accomplished by determination of VOCs characteristic for patients with H. pylori and the analysis of gases released by bacteria in suspension. Solid-phase microextraction was applied as a selective technique for preconcentration and isolation of analytes. Gas chromatography coupled with mass spectrometry was used for the separation and identification of volatile analytes in breath samples and bacterial headspace. For data calculation and processing, discriminant and factor analyses were used. Endogenous substances such as isobutane, 2-butanone and ethyl acetate were detected in the breath of persons with H. pylori in the stomach and in the gaseous mixture released by the bacteria strain but they were not identified in the breath of healthy volunteers. The canonical analysis of discrimination functions showed a strong difference between the three examined groups. Knowledge of substances emitted by H. pylori with the application of an optimized breath analysis method might become a very useful tool for noninvasive detection of this bacterium.     

Gas Diffusion Electrodes for Use in an Amperometric Enzyme Biosensor

The preparation of gas diffusion electrodes and their use in an amperometric enzyme biosensor for the direct detection of a gaseous analyte is described. The gas diffusion electrodes are prepared by covering a PTFE membrane (thickness 250 μm, pore size 2 μm, porosity 35%) with gold, platinum, or a graphite/PTFE mixture. Gold and platinum are deposited by e‐beam sputtering, whereas the graphite/PTFE layer is prepared by vacuum filtration of a respective aqueous suspension. These gas diffusion electrodes are exemplarily implemented as working electrodes in an amperometric biosensor for gaseous formaldehyde containing NAD‐dependent formaldehyde dehydrogenase from P. putida [EC. 1.2.1.46] as enzyme and 1,2‐naphthoquinone‐4‐sulfonic acid as electrochemical mediator. The resulting sensors are compared with regard to background current, signal noise, linear range, sensitivity, and detection limit. In this respect, sensors with gold or graphite/PTFE covered membranes outclass ones with platinum for this particular analyte and sensor configuration.     

The design of electrochemical probes for oxygen and chlorine and their applications in process control analysis

This paper describes the design of a membrane type polarographic probe for the determination of oxygen and chlorine in gaseous and liquid streams and of a membrane-less probe for the determination of chlorine in gaseous streams. The membrane type has limits of detection of 0.002% v/v and 0.02% v/v for oxygen and chlorine respectively and times for 80% response to step changes of 3 s and 30 s respectively. The membrane-less probe has a limit of detection of about 0.01 ppm v/v chlorine and the time taken for 80% response to a step change at the 10 ppm level is about 5 s. They can be made in a range of materials to suit particular applications. The paper gives six applications of their use in the chemical industry.     

Fluorene: An extended experimental thermodynamic study

This work reports new experimental thermodynamic results on fluorene. Vapor pressures of both crystalline and liquid phases were measured using a pressure gauge (capacitance diaphragm manometer) and Knudsen effusion methods over a wide temperature range (292.20 to 412.16) K yielding accurate determination of enthalpy and entropy of sublimation and of vaporization. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapor pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluorene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation.     

Studies of transport and collection characteristics of gaseous mercury in natural gases using amalgamation and isotope dilution analysis

Transport and collection characteristics were studied for gaseous elemental mercury (Hg(0)(g)) in natural gases using newly developed methodology based on amalgamation, isotope dilution with permeation tubes and inductively coupled plasma mass spectrometry. The study involved different Au-Pt collection tube designs, tubing materials and gaseous matrices, including air, natural and sales gas, as well as methane and sales gas to which hydrogen sulfide (H(2)S) had been added. The Hg(0)(g) capacity of the Au-Pt tubes was determined to 3.5 +/- 0.1 microg. Blanks and detection limits of gaseous mercury (Hg(g)) were 58 +/- 17 pg m(-3) and 50 pg m(-3), respectively, for a 60 L sample volume. For the gases tested, added Hg(0)(g) tracers could be collected with 90% or higher efficiency at flow rates and volumes of up to 10 L min(-1) and 100 L, respectively. The collection efficiency was found to be independent of the type of gas tested, even in the presence of H(2)S. However, for the gases containing H(2)S, the apparent transport efficiency of added Hg(0)(g) tracers through stainless steel tubing varied from 50 to 150% upon changing the temperature from 25 to 100 degrees C. The interaction of stainless steel with Hg(0)(g) leading to either a sink, or source of Hg, was not observed in the absence of H(2)S, nor was it observed for PTFE tubing in the presence of H(2)S. These observations raise questions about the applicability of currently used sampling procedures for determination of Hg(g) in H(2)S rich natural gases, including the 6978-2 ISO standard method, in which stainless steel is a prescribed material for tubing and valves of the sampling apparatus.     

Sample introduction in high speed capillary gas chromatography; input band width and detection limits

The speed of analysis in capillary gas chromatography can be substantially increased by reduction of the column inner diameter. However, special demands are then posed upon instrumental design. In particular, the sampling system is highly critical because it has to be capable of delivering extremely small injection band widths which must be compatible with the column inside diameter. This study focuses on the evaluation of two potentially suitable sample introduction systems with respect to input band width and detection limits and their compatibility with small bore (≦ 100 μm) columns in capillary gas chromatography. One of them allows liquid on-column injection, based on liquid splitting, of only a few nl onto small bore (≦ 100 ?m) fused silica columns. For gases, input band widths as low as 1 ms are obtained with this system. The other one is part of a miniaturized gas chromatograph with extremely low dead volume interfaces and detector volumes. It allows input band widths for gases of a few ms. Without any preconcentration ppm concentrations are measured in gaseous samples with a 80 ?m thick film capillary column. It will be shown that a further reduction of the minimum detectable amount and analysis time is possible with this equipment.     

Optimization of the two-phase separation process in flow-injection analysis with an electron-capture detection system

A liquid-gas-phase tubing separator was designed and its operation studied in comparison with a PTFE tape-based separator. The relative efficiencies of the two separators were compared after injection into the carrier solution of a sample containing free chlorine using a chromatographic electron-capture detector for detection in the gaseous phase. The membrane separator contained porous PTFE tape whereas the tubular separator consisted of microporous PTFE membrane tubing. The two separators were compared with respect to sensitivity and reproducibility, simplicity of design and liability to interferences. Linear ranges and free chlorine detection limits were established for each of the two separators, that of the PTFE tape-based separator being 100 μg 1^?1 and that of the tubing device 50 μg 1^?1.     

Modified cylindrical cavity-type phase separator for liquid/liquid extraction in flow-injection systems

The dimensions of a cylindrical cavity-type phase separator for liquid/liquid extraction in flow-injection analysis were examined in order to achieve smooth, long-term and efficient phase separations with good reproducibility and high sensitivity. Several kinds of filter (PTFE membrane filters and a phase-separating filter) for the organic phase were also compared. A phase separator with a cylindrical cavity (4.2-mm diameter, 2.3-mm deep) and a conical cavity (5-mm diameter, 1.7-mm deep) was the most desirable. A less expensive phase-separating filter can be used instead of a PTFE membrane filter.     

A biochemical sniffer-chip for convenient analysis of gaseous formaldehyde from timber materials

A biochemical gas-sensor (sniffer-chip) with formaldehyde dehydrogenase (FALDH) was developed for convenient analysis of gaseous formaldehyde with high gas-selectivity. The sniffer-chip for formaldehyde in the gas phase was constructed by immobilizing FALDH to a Pt-electrode coated hydrophilic PTFE membrane. The oxidation current of NADH produced by the enzymatic reactions was measured by amperometric analysis. The calibration range of the sniffer-chip for formaldehyde in the gas phase was from 40 to 2000 ppb, which encountered the maximum permissible concentration of formaldehyde vapor in the residential house (80 ppb) and formaldehyde detection limit for the human sense of smell (410 ppb). As the resident-environmental application, the sniffer-chip was possible to measure the formaldehyde concentration from some timber materials (3 kinds of interior timber and 2 kinds of exterior formwork timber) within 3 min. The calculated concentration value by a regression analysis was consistent with those of a commercially available gas sensor and a gas detector tube for formaldehyde. The FALDH sniffer-tip would be effective and convenient approach to detect and measure gaseous formaldehyde with high gas-selectivity at the residential atmosphere. Correspondence: Kohji Mitsubayashi, Department of Biomedical Devices and Instrumentation, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan     

Reduction and Elimination of Humic Acid Fouling in Air Sparged Membrane Distillation Using Nanocarbon Immobilized Membrane

In this paper, we present the treatment of humic acid solution via carbon nanotube immobilized membrane (CNIM) distillation assisted by air sparging (AS). Carbon nanotubes offer excellent hydrophobicity to the modified membrane surface and actively transport water vapor molecules through the membrane to generate higher vapor flux and better rejection of humic acid. The introduction of air sparging in the membrane distillation (MD) system has changed the humic substance fouling by changing the colloidal behavior of the deposits. This modified MD system can sustain a higher run time of separation and has enhanced the evaporation efficiency by 20% more than the regular membrane distillation. The air sparging has reduced the deposition by 30% in weight and offered lesser fouling of membrane surface even after a longer operating cycle. The water vapor flux increased with temperature and decreased as the volumetric concentrating factor (VCF) increased. The mass transfer coefficient was found to be the highest for the air sparged—carbon nanotube immobilized membrane (AS-CNIM) integrated membrane distillation. While the highest change in mass transfer coefficient (MTC) was found for polytetrafluoroethylene (PTFE) membrane with air sparging at 70 °C.     

Sampling small volumes of ambient ammonia using a miniaturized gas sampler

The development of a gas sampler for a miniaturized ambient ammonia detector is described. A micromachined channel system is realized in glass and silicon using powder blasting and anodic bonding. The analyte gas is directly mixed with purified water, dissolving the ammonia that will dissociate into ammonium ions. Carrier gas bubbles are subsequently removed from the liquid stream through a venting hole sealed with a microporous water repellent PTFE membrane. A flow restrictor is placed at the outlet of the sampler to create a small overpressure underneath the membrane, enabling the gas to leave through the membrane. Experiments with a gas flow of 1 ml min(-1), containing ammonia concentrations ranging from 9.4 ppm to 0.6 ppm in a nitrogen carrier flow have been carried out, at a water flow of 20 microl min(-1). The ammonium concentration in the sample solution is measured with an electrolyte conductivity detector. The measured values correspond with the concentration calculated from the initial ammonia concentration in the analyte gas, the fifty times concentration enhancement due to the gas-liquid volume difference and the theoretical dissociation equilibrium as a function of the resulting pH.     

Study of new protective clothing against SARS using semi-permeable PTFE/PU membrane

Chemicals which may pose a hazard to people upon contact may be in several forms, such as liquid, mist, vapor, etc. The damage caused can range from mild skin diseases to more serious chronic illnesses. Therefore, chemical protective clothing must be used to safe some personal who may be exposed to hazardous chemicals. The use of PTFE/PU membrane for chemical protective clothing is discussed in the article. By means of texturing with organic conductive fiber, and then treating with JAM-Y1 anti-bacteria agent, in the end, treating with the XL-550 waterproof agent, the PET fabric has permanent anti-static, anti-bacteria and waterproof and anti-oil properties. The PTFE/PU protective material is prepared by laminating with PET fabric by paste dot coating, and then coated by PU solution in a direct process. The PU coating agent, DMF and acetone, are used in testing through surface tension and peeling strength measurement. The penetration property of poliomyelitis virus in liquid and animalcule in air of PTFE membrane laminated textile, after being coated by PU solution are measured. The results show that it can separate SARS virus in air and liquid, and WVT is 11496 g/24 h m². Then it can provide a satisfactory wearing comfort.     

Encapsulation of ionic liquids within polymer shells via vapor phase deposition

We demonstrate the use of vapor phase deposition to completely encapsulate ionic liquid (IL) droplets within robust polymer shells. The IL droplets were first rolled into liquid marbles using poly(tetrafluoroethylene) (PTFE) particles because the marble structure facilitates polymerization onto the entire surface area of the IL. Polymer shells composed of 1H,1H,2H,2H-perfluorodecyl acrylate cross-linked with ethylene glycol diacrylate (P(PFDA-co-EGDA)) were found to be stronger than the respective homopolymers. Fourier transform infrared spectroscopy showed that the PTFE particles become incorporated into the polymer shells. The integration of the particles increased the rigidity of the polymer shells and enabled the pure IL to be recovered or replaced with other fluids. Our encapsulation technique can be used to form polymer shells onto dozens of droplets at once and can be extended to encapsulate any low vapor pressure liquid that is stable under vacuum conditions.     

Modification of Simha–Somcynsky equation of state for small and large molecules

The Simha–Somcynsky equation of state (SS EOS) represents the PVT behavior of polymers quite satisfactorily, but cannot be applied to gases at low pressures. This work proposes a modification of the free volume contribution of the SS EOS to allow representation of gaseous state of low molecular-weight substances by introducing the perturbed hard-chain theory of Beret and Prausnitz into the EOS. In addition to this modification, two universal constants are introduced to the free volume term for better representation of properties of low molecular-weight substances. Characteristic parameters in the modified SS EOS were determined for 44 low molecular-weight substances and 64 polymers. The absolute average deviations (AADs) for critical temperature, critical pressure and vapor pressures were 0.86, 2.38 and 2.01%, respectively, while AAD for critical density and saturated liquid density at normal boiling point were somewhat larger, being 20.46 and 5.30%, respectively. The high performance of the original SS EOS for polymer PVT behavior was maintained in the modified EOS with grand AAD of 0.050% for densities.     

Thermodynamic Stability of Fenclorim and Clopyralid

The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.