A new gas inlet system for an isotope ratio mass spectrometer improves reproducibility

We have developed a new inlet system for a gas sample isotope ratio mass spectrometer (IRMS). It is based on the well-known open split design from the gas chromatography/mass spectrometry (GC/MS) system due to its simplicity. The advantages over the conventional double inlet system with the metal bellows design include an improved reproducibility mainly due to a highly controllable pressure and temperature adjustment, a markedly lowered memory effect due to an uninterrupted gas flow through the ion source which limits adsorption/desorption processes on surfaces, and a single inlet capillary circumventing problems of asymmetrical behavior of sample and reference inlet paths. Furthermore, sample consumption is of the same order as for conventional measurements (i.e. about 0.4 mmol per hour), of which however only 2 &mgr;mol/h is used for the actual isotope ratio determination since the major gas amount acts as a gas flow seal against the atmosphere, corresponding to a 100-200 fold overkill. This may be improved in future systems. Copyright 2000 John Wiley & Sons, Ltd.     

Reduction of nitric oxide to elemental nitrogen byThiobacillus Denitrificans

A need exists for new technology for the disposal of concentrated NO_x streams obtained from certain regenerable, dry scrubbing processes, such as the NOXSO process, and the removal and disposal of NO_x from more dilute gas streams produced by nitric acid plants. It has been demonstrated that the facultative anaerobe and autotroph, Thiobacillus denitrificans, may be cultured anaerobically in batch reactors using NO (g) as a terminal electron acceptor. Thiosulfate served as an energy source, CO₂ (g) as a carbon source, and ammonium ion as a source of reduced nitrogen. The growth of T.denitrificans was indicated by depletion of thiosulfate and ammonium ion and the accumulation of biomass. The feed gas consisted of 5000 ppmv NO, 5%, CO₂, and balance nitrogen. The NO concentration in the outlet gas was typically 200 ppmv.     

Pyrrole-based conductive polymer as the solid-phase extraction medium for the preconcentration of environmental pollutants in water samples followed by gas chromatography with flame ionization and mass spectrometry detection

A pyrrole-based polymer was synthesized and applied as a new sorbent for solid-phase extraction (SPE) of some environmental pollutants from water samples. Polypyrrole (PPy) was synthesized by chemical oxidation of the monomer in nonaqueous solution. SPE of selected phenols, pesticides, and polyaromatic hydrocarbons (PAHs) from aqueous samples were performed using 200 mg PPy. The determination was subsequently carried out by gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The polymer showed much higher recoveries for aromatic compounds than aliphatics. Preconcentration of sample volumes up 11 led to acceptable recoveries for aromatic and other tested polar compounds. The R.S.D. for a river water sample spiked with phenols, pesticides and PAHs at sub-ppb level was lower than 10% (n = 3) and limits of detection for these compounds were between 15 and 120 ng l(-1).     

Trimethylsilyl-O-methyloxime derivatives for the measurement of [6,6-2H2]-D-glucose-enriched plasma samples by gas chromatography-mass spectrometry.

A new method for the determination of the enrichment of [6,6-2H2]-D-glucose in human plasma by gas chromatography-mass spectrometry (GC-MS) is described. (2,3,4,5,6)-Pentakis-O-trimethylsilyl-O-methyloxime-D-glucose is used as a derivative for the GC measurement. Using GC-MS with electron-impact ionization, the enrichment is measured in the single-ion monitoring mode observing the masses m/z 319 and 321. In contrast to other methods the use of this glucose derivative reduced the amount of plasma needed from 200 to 10 microliters and no chemical ionization equipment is needed for the mass spectrometer.     

Isothermal evaporation of ethanol in a dynamic gas atmosphere

Optimization of evaporation and pyrolysis conditions for ethanol are important in carbon nanotube (CNT) synthesis. The activation enthalpy (ΔH(?)), the activation entropy (ΔS(?)), and the free energy barrier (ΔG(?)) to evaporation have been determined by measuring the molar coefficient of evaporation, k(evap), at nine different temperatures (30-70 °C) and four gas flow rates (25-200 mL/min) using nitrogen and argon as carrier gases. At 70 °C in argon, the effect of the gas flow rate on k(evap) and ΔG(?) is small. However, this is not true at temperatures as low as 30 °C, where the increase of the gas flow rate from 25 to 200 mL/min results in a nearly 6 times increase of k(evap) and decrease of ΔG(?) by ~5 kJ/mol. Therefore, at 30 °C, the effect of the gas flow rate on the ethanol evaporation rate is attributed to interactions of ethanol with argon molecules. This is supported by simultaneous infrared spectroscopic analysis of the evolved vapors, which demonstrates the presence of different amounts of linear and cyclic hydrogen bonded ethanol aggregates. While the amount of these aggregates at 30 °C depends upon the gas flow rate, no such dependence was observed during evaporation at 70 °C. When the evaporation was carried out in nitrogen, ΔG(?) was almost independent of the evaporation temperature (30-70 °C) and the gas flow rate (25-200 mL/min). Thus the evaporation of ethanol in a dynamic gas atmosphere at different temperatures may go via different mechanisms depending on the nature of the carrier gas.     

Element Specific GC-Detection by Plasma Atomic Emission Spectroscopy—A Powerful Tool in Environmental Analysis

Abstract

A new Plasma Emission Detector (FED) to be used in gas chromatography has been developed, consisting of a capacitively coupled helium plasma operating at 200 W and 27 MHz and a poly-chromator system. Elements such as H, C, N, O, S, F, Cl, Br and I can be simultaneously detected, giving way to new possibilities of measuring organic environmental pollutants.

1. Non-separated compounds can be easily measured with the FED, as long as the compounds contain different hetero-elements.

2. The calibration for a complex system as for example the chlorinated HC's demands only for a single standard.

3. The simultaneous detection of all elements of a separated compound allows the calculation of the total molecular formula.

The detection limits for different elements lie between 50 and 200 pg/sec at a signal to noise ratio of 3 to 1.     

ICP-MS 法直接测定冰芯样品中超痕量镉

采用 ICP- MS法对冰芯样品中超痕量 Cd的直接测定进行了研究。确定了直接测定浓度为 pg/m L 级的 Cd的最佳仪器参数、载气流速、进样速度等与灵敏度之间的关系以及浓度和扫描参数对分析精度的影响。本方法对浓度 5～2 0 0 pg/m L Cd的分析 ,RSD<1 0 % ,回收率在 88%～ 1 0 5%之间 ,检测限为0 .1 5pg/m L     

Evaluation of a hypercrosslinked polystyrene, MN-200, as a sorbent for the preconcentration of volatile organic compounds in air

Breakthrough volumes, average percentage recoveries, and storage stabilities were obtained for vapors of 8 volatile organic compounds (pentane, octane, undecane, isooctane, cyclohexane, toluene, methanol, and dichloromethane) on a new adsorbent material, Hypersol-Macronet, MN-200. Breakthrough volumes were estimated as half of the gas chromatographic specific retention volumes at 20 degrees C for the compounds. Recoveries of the adsorbates were determined by both solvent extraction and thermal desorption methods. The results obtained compare favorably with those for Tenax GR (values reported in the published literature and others obtained in our laboratory). Results of storage stability studies on MN-200 meet the criterion for acceptability (<10% loss). High adsorption capacity for very volatile and polar compounds, combined with ease of desorption of less volatile compounds, render MN-200 a highly promising adsorbent for sampling volatile organic compounds in indoor and outdoor air.     

Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part II: Heptakis(3-O-acetyl-2,6-di-O-pentyl)-ß-cyclodextrin

Heptakis (3-O-acetyl-2,6-di-O-pentyl)-ß-cyclodextrin is used as a chiral stationary phase in capillary gas chromatography. High enantioselectivity towards trifluoro-acetylated α and β-chiral amines, amino alcohols, α- and β-amino acid esters, and cyclic trans-diols is observed. In contrast to chiral polysiloxane phases, where hydrogen bonding interaction is essential for enantiomer separation, in cyclodextrins inclusion properties contribute to enantioselectivity. This can be concluded from the separation of N-alkylated amino compounds. The new chiral stationary phase exhibits a wide operating temperature range and is stable above 200°C.     

Effect of different target gases on low-energy collision-activated dissociation of peptides

Experimental variables affecting the daughter-ion spectra of a series of protonated peptides [MH]+, produced by fast-atom bombardment ionization, using a low energy (0-450 eV) quadrupole collision cell are investigated. The parameters studied include target gas pressure, collision energy, cross-sectional area and acidity of the target gas. The results show that low-mass immonium ions are preferentially formed both at high collision energies (greater than 200 eV) and at target gas pressures greater than 10(-6) mBar (where multiple collisions occur in the gas cell). Positive fragment ion abundance is maximized when acidic gases are used as the target gases, and this is rationalized on the basis of a proton-transfer reaction from the target gas to the amide nitrogen of the peptide bond promoting fragmentation.     

Metabolic profiling of urinary organic acids by single and multicolumn capillary gas chromatography

High-resolution gas chromatography (HRGC) and gas chromatography/mass spectrometry (GC/MS) are the techniques of choice to determine the retention indices of more than 200 organic acids as their trimethylsilyl (TMS) or oxime-trimethylsilyl derivatives. Several types of apolar and semipolar fused-silica capillary columns (OV-1, SE-52, and OV-1701), used to analyze and separate organic acids isolated from urine samples, are evaluated.     

Headspace gas chromatographic determination of 1,4-dioxane with adsorption preconcentration on silica modified with λ-carrageenan

Organosilica materials containing λ-carrageenan on their surface are synthesized. The conditions for the immobilization of the polysaccharide, such as phase contact time and pH and concentration of solutions, are optimized. It is shown that the chemisorption of the polysaccharide passes through ion exchange multipoint immobilization, which provides a high hydrolytic stability of the prepared organosilica. The rate of washing of λ-carrageenan to the solution does not exceed 0.5%. The physical and chemical characteristics of the new material are studied. In particular, it is shown that the material is completely stable up to 200°C and reversibly desorbs water at 120°C; it well adsorbs 1,4-dioxane from the gas phase and desorbs it under heating to 70°C. This ensures the use of the prepared carrageenan-containing material as an adsorbent for a solid-phase cartridge designed for the adsorption preconcentration of 1,4-dioxane in its headspace gas chromatographic determination in samples of nonionic surfactants. The developed procedure ensures the determination of 1,4-dioxane by gas chromatography with a flame ionization detector in the concentration range 0.012–3.750 mg/L with a limit of detection of 0.0014 mg/L. Preconcentration lowers the limit of detection in the determination of 1,4-dioxane by 50 times.     

Emission spectra of an argon inductively coupled plasma in the vacuum ultraviolet: background spectra from 85 to 200 nm

The background spectra emitted from an argon ICP discharge have been recorded over the spectral range 85 to 200 nm. These vacuum ultraviolet spectra were acquired by coupling the ICP to a 0.5-m Seya-Namioka vacuum monochromator, through a helium purged side-arm. Background features observed include emission from the resonance lines of ArI, and emission from gas impurities such as oxygen, nitrogen, carbon and hydrogen.     

Vibrational energy transfer in N2-N2 collisions: a new semiclassical study

The vibrational energy relaxation in collisions between N2 molecules in the low- and medium-lying vibrationally excited levels was revisited using the semiclassical coupled-state method and the use of two different potential-energy surfaces having the same short-range potential recently determined from ab initio calculations but with different long-range interactions. Compared to the data reported in the classical work by Billing and Fisher [Chem. Phys. 43, 395 (1979)], the newly calculated vibration-to-translation rate constant K(1,0 / 0,0) is in much better agreement with the available experimental data over a large temperature interval, from T = 200 K up to T = 6000 K. Nevertheless, as far as the vibration-to-translation exchanges are concerned, the lower-temperature regime remains quite critical in that the new rate constants do not completely account for the rate constant curvature suggested by the experiments for temperatures lower than T = 500 K. The dependence of the state-selected vibration-to-vibration rate constants, K(v,v-delta v / 0,1), both upon the vibrational quantum number v and the gas temperature are calculated. The substantial deviations from previously found behaviors could have major consequences for the vibrational kinetic modeling of N2-containing gas mixtures.     

Synthesis of single crystalline tellurium nanotubes with triangular and hexagonal cross sections

Single crystalline tellurium (Te) nanotubes with triangular cross sections were successfully synthesized for the first time by a simple approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a suitable substrate. Tellurium gas was evaporated by heating at 350 degrees C and was condensed on the Si (100) substrate at 150-200 degrees C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 10 min. This led to the production of nanotubes of triangular cross section along with some hexagonal ones. The formation of the nanotubes was highly dependent upon the structure of the substrate surface, Ar gas flow rate, and the deposition temperature. When the substrate is Si (111) or sapphire (0001) or when the argon flow rate is increased to 500 sccm, nanowires and nanorods were exclusively formed. Irrespective of the morphologies, all the observed Te nanostructures grew in a regular [0001] direction. The facile approach to nanotubes with a triangular cross section may facilitate some new applications as well as stimulate theoretical studies pertaining to the stability of this high-energy configuration.     

Determination of aliphatic amines using N-succinimidyl benzoate as a new derivatization reagent in gas chromatography combined with solid-phase microextraction

A simple, selective and sensitive approach was developed for the quantitation of aliphatic amines in lake water applying a new reagent (N-succinimidyl benzoate, SIBA), synthesized in the laboratory of the authors. Derivatization of the n-C1-C6 aliphatic monoamines and dimethylamine in aqueous solution with SIBA was followed by headspace solid-phase microextraction (SPME). Derivatives were identified by gas chromatography-mass spectrometry and determined by gas chromatography-flame ionization detection. Both derivatization and SPME conditions have been optimized. Derivatizations were performed in borate buffer (pH 8.8), at 60 degrees C for 22 min. SPME was carried out from saturated sodium chloride solution, at 80 degrees C for 60 min, desorption at 250 degrees C for 2 min. Detection limit of derivatized amines proved to be 0.13-7.2 nmol/l, while recovery of amines from lake water samples, in the concentration range of 100-200 microg/l, varied from 94.1 to 102.7%.     

Molecular kinetic aspects of vaporization of volatile coordination compounds with organic ligands

We present results of the experimental study and numerical simulation of radiation-convective heat and mass transfer during the sublimation of spherical particles of metal β-diketonates in a high-temperature inert gas flow (argon or helium). The sublimation process is visualized, and experimental data on the temperature variation dynamics and particle size are obtained. It is shown that at stable transfer of the compound from the particle surface the sublimation proceeds with the formation of large pores in its structure. The effect of inert gas properties on the kinetics of the vaporization process of precursor particles with various initial diameters is analyzed in the temperature range from 200 °C to 330 °C. Due to a higher thermal conductivity and heat capacity of helium as compared with argon, the choice of helium as carrier gas causes an increase in the sublimation intensity.     

生物油水蒸气气化实验研究

利用固定床反应器对生物油的水蒸气非催化气化性能进行了实验研究,考察了温度和水蒸气的加入量对气化过程的影响,对气化所得粗合成气的组成分布进行了分析。结果表明,升高温度有利于生物油向合成气转化,1 200 ℃时,生物油的碳转化率可达97.8%,合成气有效成分(H₂+CO)的产率可达77%,其中H₂/CO摩尔比为1.19;水蒸气的加入可以提高合成气中的H₂/CO摩尔比,当S/C(水碳比)=4时,合成气中的H₂/CO摩尔比可达3.69,与此同时,水蒸气的加入不利于合成气有效成分产率的提高;生物油气化所得气体为中热值气体。     

Charge-stripping system for 238U ion beam with recirculating He gas

Recent developments in a charge-stripping system employing high-flow rate He gas circulation (~200 L/min) for ²³⁸U³⁵⁺ beams injected at 10.8 MeV/u are reported. He gas is confined in a target section and is separated from a vacuum duct using five-stage differentially-pumped sections. To minimize the gas leakage rate via beam apertures, a high-performance differential pumping was required. To avoid huge gas consumption, a clean gas recycling with high-flow rate was simultaneously required. To realize these, we developed multi-stage mechanical booster pump array. The recycling rate of He gas was achieved as more than 99 %. The system performance has been checked with the present maximum beam current up to 13 eμA (~1 kW beam power).     

Radial dose distribution around a heavy ion''s path

Ionization currents produced in a small wall-less ionization chamber located at varying distance from the 200 MeV Ni¹²⁺ ion's path traversing Ar gas were measured and utilized to construct a track structure model. Using the LET value of 200 MeV Ni¹²⁺ and G(Fe³⁺) in Fricke solutions (= 15.4) for fast electrons, we estimate G(Fe³⁺) for 200 MeV Ni¹²⁺ to be 5.0.