Quantification of volatile compounds in the headspace of aqueous liquids using selected ion flow tube mass spectrometry

We describe a method by which the concentrations of volatile compounds in the headspace of their dilute aqueous solutions in sealed containers can be determined using on-line selected ion flow tube mass spectrometry (SIFT-MS). Thus, the changing number density of the molecules of the volatile compound in the carrier gas of the SIFT-MS instrument is described in terms of its changing flow rate as the pressure in the sealed container decreases during the sampling procedure. It is shown that the best analytical procedure is to determine the mean concentration of the trace gas in the liquid headspace over a given sampling time and relate this to the required concentration, which is the initial equilibrium concentration established before the pressure in the sealed container reduces significantly. To test the validity of this analytical approach, the headspace concentrations of acetaldehyde, ethanol and acetone above aqueous solutions of known concentrations have been determined. Hence, the Henry's Law constants for these compounds have been determined and found to agree with the published values. The confirmation of the quality of this sampling methodology combined with SIFT-MS for the analysis of volatile compounds in liquid headspace paves the way for the rapid analyses of biological liquids such as urine and serum for clinical diagnosis and physiological monitoring.     

On the influence of nitrogen and oxygen on the GD-OES analysis results

Summary The effect of nitrogen and oxygen impurities in argon on the analytical line intensity of various elements and other discharge parameters of a dc glow discharge has been studied. The two gaseous impurities were introduced into the discharge gas argon as molecular gaseous additions as well as sputtering products from the samples. Both elements may initiate chemical reactions in the plasma leading to a reduction of the number of free atoms of the determined elements available for excitation in the discharge plasma. Considering the main components of the investigated sample, nitrogen or oxygen contents exceeding the critical threshold of about 0.1 mass-% may alter the analytical line intensities of the elements of interest significantly. The effect of smaller gaseous impurity contents could be detected only by the determination of the emission yield. The line intensity may increase or decrease depending on the elements present in the discharge plasma.     

Suitability of different containers for the sampling and storage of biogas and biomethane for the determination of the trace-level impurities – A review

The traceable and accurate measurement of biogas impurities is essential in order to robustly assess compliance with the specifications for biomethane being developed by CEN/TC408. An essential part of any procedure aiming to determinate the content of impurities is the sampling and the transfer of the sample to the laboratory. Key issues are the suitability of the sample container and minimising the losses of impurities during the sampling and analysis process. In this paper, we review the state-of-the-art in biogas sampling with the focus on trace impurities. Most of the vessel suitability studies reviewed focused on raw biogas. Many parameters need to be studied when assessing the suitability of vessels for sampling and storage, among them, permeation through the walls, leaks through the valves or physical leaks, sorption losses and adsorption effects to the vessel walls, chemical reactions and the expected initial concentration level. The majority of these studies looked at siloxanes, for which sampling bags, canisters, impingers and sorbents have been reported to be fit-for-purpose in most cases, albeit with some limitations. We conclude that the optimum method requires a combination of different vessels to cover the wide range of impurities commonly found in biogas, which have a wide range of boiling points, polarities, water solubilities, and reactivities. The effects from all the parts of the sampling line must be considered and precautions must be undertaken to minimize these effects. More practical suitability tests, preferably using traceable reference gas mixtures, are needed to understand the influence of the containers and the sampling line on sample properties and to reduce the uncertainty of the measurement.     

烷烃混合物在Cu-BTC中的吸附与分离

用巨正则系综Monte Carlo (GCMC)和构型导向Monte Carlo (CBMC)相结合的方法模拟了298 K下甲烷-乙烷-丙烷体系以及正丁烷-异丁烷体系在1,3,5-苯三甲酸铜(II) (Cu-BTC)中的吸附行为. 结果表明, Cu-BTC对丙烷以及异丁烷的吸附分离都有较好的选择性. 通过我们发展的“材料剖面成像”方法研究了烷烃混合物在Cu-BTC中不同压力下的吸附位点, 从而进一步分析了烷烃混合物在Cu-BTC中的分离性能. 结果发现, 在吸附过程中主要存在着两种效应, 即能量效应和尺寸效应的竞争. 在甲烷-乙烷-丙烷体系中, 较高压力下, 由于尺寸效应的影响, 丙烷主要吸附在主孔道中, 而对甲烷和乙烷组分, 能量效应占主导地位, 从而导致乙烷主要吸附在四面体孔内, 甲烷则主要吸附在三角形孔窗外. 在正丁烷-异丁烷体系中, 能量效应起主导作用, 从而使异丁烷主要吸附在四面体孔内, 而正丁烷主要吸附在主孔道中.     

The long-time reactor irradiation of biological material at reduced temperature

When biological material in closed quartz ampoules is irradiated gaseous reaction products are formed as a result of radiation damage and thermal decomposition. The pressure thus created in the ampoules puts a limit to the time of irradiation or the sample mass and thereby to the detection limit of neutron activation analysis. The investigation will show how the internal pressure of the ampoules is reduced by cooling the sample containers in a nitrogen bath during irradiation so that a number of trace elements also in fresh biological material can be detected by means of neutron activation analysis with long-time irradiation. It will further contain a methodical study of the mechanical strength of quartz ampoules used as sample containers and the change in sample temperature using different sample containers and cooling through different media. The results of two irradiation studies of biological material in the low temperature irradiation unit of the reactor Melusine of the CENG Grenoble will be discussed.     

Gas chromatographic analysis of trace gas impurities in tungsten hexafluoride

Highly reactive fluorinated gaseous matrices require special equipment and techniques for the gas chromatographic analysis of trace impurities in these gases. The impurities that were analysed at the low-microg/l levels included oxygen, nitrogen, carbon dioxide, carbon monoxide, sulfur hexafluoride and hydrogen. This paper describes the use of a system utilising backflush column switching to protect the columns and detectors in the analysis of trace gas impurities in tungsten hexafluoride. Two separate channels were used for the analysis of H2, O2, N2, CO, CO2 and SF6 impurities with pulsed discharge helium ionisation detection.     

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.     

FTIR and GC as complementary tools for analysis of corrosive gases

The gas metrology laboratory of the National Metrology Institute of South Africa has developed methodology for the gravimetric preparation of corrosive gas mixtures such as nitric oxide (NO) in nitrogen, as well as sulphur dioxide (SO₂) in nitrogen or synthetic air. Fourier transform infrared (FTIR) spectroscopy has been used to analyse for trace and ultra trace levels of infrared active gaseous species, such as NO, nitrogen dioxide and SO₂ that are difficult to analyse by other means. These corrosive gas mixtures are also analysed using gas chromatography with pulsed helium ionisation detection to complement the work done using FTIR with infrared active impurities. A comparison between the techniques of FTIR, gas chromatography and non-dispersive infrared spectroscopy for corrosive gas analysis is also presented.     

用于负压下气体分析的气相色谱仪的研制

介绍一种可同时分析负压样品中常量Ｏ２,Ｎ２,ＣＯ和微量ＣＯ２的自制专用气相色谱仪。仪器在 负压下取样,经活塞升压后进样。在流程中样品气同时进入并列的色谱柱,再分别检测。常量组分使用热导池检测,微量组分使用氦离子化检测器检测。ＣＯ２的检测灵敏度为１０＾－６量级。实验表明,仪器结构简单,操作方便稳定性好,适合于负压气样的在线分析,负压气样中全组分的分析方法具有推广价值。     

High pressure chemistry in a Fourier transform ion cyclotron resonance mass spectrometer using a split-pair magnet

A new experimental method has been developed to probe ion/molecule reactions at gas pressures up to 0. 1 torr. A Fourier transform ion cyclotron resonance (FTICR) mass spectrometer has been constructed to trap ions within the trapped ion cell at these pressures for time intervals up to several hundred milliseconds, allowing the ions to undergo several million collisions. Multiple pulsed valves inject the gaseous reagents in brief, high pressure bursts. A unique, high conductance vacuum chamber rapidly reduces the gas pressure from as high as 0.01 torr to near background pressures in 2–5 s for optimum operation of the FTICR for identifying the ionic products. A pressure of 0.1 torr is attainable but results in slower gas evacuation. High pressure operation of this instrument is demonstrated for ion chemistry in silane, argon, and silicon tetrafluoride. Pressures are sufficiently high to allow termolecular formation of adducts with the trapped ion cell. Negative ion formation in silane has greatly improved efficiency due to the high pressure ionization. Trace impurities at the ppm level in argon and silicon tetrafluoride are detected through chemical ionization afforded by the large number of ion/molecule collisions.     

The novel use of gas chromatography-ion mobility-time of flight mass spectrometry with secondary electrospray ionization for complex mixture analysis

Increasing the dimensionality of an analysis enables more detailed and comprehensive investigations of complex mixtures. One dimensional separation techniques like gas chromatography (GC) and ion mobility spectrometry (IMS) provide limited chemical information about complex mixtures. The combination of GC, ion mobility spectrometry, and time-of-flight mass spectrometry (GC-IM-TOFMS) provides three-dimensional separation of complex mixtures. In this work, a hybrid GC-IM-TOFMS with a secondary electrospray ionization (SESI) source provided four types of analytical information: GC retention time, ion mobility drift time, mass-to-charge ratios, and ion intensity. The use of secondary electrospray ionization enables efficient and soft ionization of gaseous sample vapors at atmospheric pressure. Several complex mixtures, including lavender and peppermint essential oils, were analyzed by GC-SESI-IM-TOFMS. The resulting 3D data from these mixtures, each containing greater than 50 components, were plotted as 3D projections. In particular, post-processed data plotted in three dimensions showed that many mass selected GC peaks were resolved into different ion mobility peaks. This technique shows clear promise for further in-depth analyses of complex chemical and biological mixtures.     

A semi-automatic system for activation analysis using the WWR nuclear reactor

A semi-automatic pneumatic transport system for nuclear reactors is described. The sealed polyethylene capsules containing the sample are placed into transport containers. Ten such containers are placed manually into a feeding device. All subsequent operations (irradiation, removal of the capsule from the container, and transport of the capsule to the laboratory for activity measurement) are automated. Total time from the completion of irradiation to the beginning of measurement is 10–20 sec.     

非晶硅太阳能电池生产工艺用氣分析方法研究

本文对非晶硅太阳能电池制造工艺过程所用的无机氢化物烷类气体硅烷、硼烷、磷烷、甲烷和氢及其混合气的配制与分析方法进行了研究,以微机控制配气、检测程序、气相色谱法分成分析杂质,电容法测水分,方法已应用于工艺过程分析。     

High-Flux Irradiation of Open Samples

The irradiation of large samples of biological material in a high neutron flux enables the extention of trace element analysis into the ng to pg range, but raises several problems as gamma heating and radiolysis degrade the samples. Gamma heating increases the pressure to a point where either a very large irradiation container is necessary or a container which can endure the high pressure. Several methods to overcome these problems have been published. The irradiation of open samples was performed as an alternative to these methods. Temperature effects on biological material during irradiation in a high and in a low neutron flux were compared. As an example, wheat was irradiated in open containers allowing simultaneous temperature measurement in the sample during irradiation.     

Potential of mass spectrometry for the analysis of inorganic high-temperature vapors

Mass spectrometry is the most versatile method for the analysis of high-temperature vapors, because it enables the identification of the gaseous species and the determination of their partial pressures. If the vaporization processes are conducted under thermodynamic equilibrium, thermodynamic data can be evaluated from the partial pressures and their temperature-dependencies. The mass spectrometric methods used for the determination of thermodynamic data of high-temperature vapors are Knudsen effusion mass spectrometry (KEMS), transpiration mass spectrometry (TMS), and laser-induced vaporization mass spectrometry (LVMS). KEMS is used whenever possible. Limitations of KEMS and TMS are the container problem, which limits the measurement temperatures to approximately 2500 K. The container problem is overcome by LVMS, which enables measurements up to approximately 7000 K. The upper limit of the partial pressure measurement by KEMS of approximately 10 Pa does not apply for TMS, which enables measurements up to pressures of approximately 0.1 MPa. The fundamentals of the different methods are described and results are presented. Emphasis is on KEMS.     

Potential of mass spectrometry for the analysis of inorganic high-temperature vapors

Mass spectrometry is the most versatile method for the analysis of high-temperature vapors, because it enables the identification of the gaseous species and the determination of their partial pressures. If the vaporization processes are conducted under thermodynamic equilibrium, thermodynamic data can be evaluated from the partial pressures and their temperature-dependencies. The mass spectrometric methods used for the determination of thermodynamic data of high-temperature vapors are Knudsen effusion mass spectrometry (KEMS), transpiration mass spectrometry (TMS), and laser-induced vaporization mass spectrometry (LVMS). KEMS is used whenever possible. Limitations of KEMS and TMS are the container problem, which limits the measurement temperatures to approximately 2500 K. The container problem is overcome by LVMS, which enables measurements up to approximately 7,000 K. The upper limit of the partial pressure measurement by KEMS of approximately 10 Pa does not apply for TMS, which enables measurements up to pressures of approximately 0.1 MPa. The fundamentals of the different methods are described and results are presented. Emphasis is on KEMS.     

Massenspektrometrische Untersuchungen binärer Mischungen aus Alkalimetall- und Erdalkalimetallhalogeniden

Mass Spectrometrical Investigations of Binary Mixtures Alkali Halide – Alkaline Earth Halide The vapor composition of some binary mixtures alkali halide – alkaline earth halide was investigated by high-temperature mass spectrometry. Concentrations of all molecules in gas phase in dependence on the molar composition of liquid mixture were studied. In the vapors over all mixtures exist gaseous heterocomplexes. With increasing radius of the anion a tendency of decreasing stabilities of 1:1 heterocomplexes is stated. The absolute content of gaseous complexes is a function of the ratio of the vapor pressures of the pure components of mixtures. Calculated formation enthalpies fo various stoichiometric heterocomplexes are given.     

Indirect hydrogen analysis by gas chromatography coupled to mass spectrometry (GC–MS)

Gas chromatography (GC) is an analytical tool very useful to investigate the composition of gaseous mixtures. The different gases are separated by specific columns but, if hydrogen (H₂) is present in the sample, its detection can be performed by a thermal conductivity detector or a helium ionization detector. Indeed, coupled to GC, no other detector can perform this detection except the expensive atomic emission detector. Based on the detection and analysis of H₂ isotopes by low‐pressure chemical ionization mass spectrometry (MS), a new method for H₂ detection by GC coupled to MS with an electron ionization ion source and a quadrupole analyser is presented. The presence of H₂ in a gaseous mixture could easily be put in evidence by the monitoring of the molecular ion of the protonated carrier gas. Copyright © 2013 John Wiley & Sons, Ltd.     

Sample Preparation Techniques—An Important Part in Trace Element Analysis for Environmental Research and Monitoring

Abstract

For the determination of minute amounts of elements in environmental samples combined analytical procedures are frequently employed. The combination of suitable sample preparation techniques with adequate detection methods lead to powerful analytical procedures. Decomposition methods are an important part of combined procedures for the determination of trace elements in solid samples. After a short summary of the potential sources for systematic errors two new decomposition methods are described that are suitable for the ashing of organic environmental samples. In one method the organic sample is ashed in a high-frequency excited oxygen plasma. The second method is a high pressure decomposition that permits mineralization of the sample in sealed quartz vessels with nitric acid at temperatures up to 320°C.

For both methods the ratio of sample weight to decomposition reagents is comparatively high. This makes these methods in combination with adequate detection methods suitable for the determination of elements at very low concentrations.

X-ray fluorescence spectrometry combined with adequate preconcentration methods is very well suited for the simultaneous determination of trace elements. Following a critical evaluation of various preconcentration techniques the analytical characteristics of filter paper with immobilized complexing agents are described. Particular emphasis is given to filter papers with dithiocarbamates as chelating group.     

Service oxygen analyses with 14 mev neutrons at iowa state university

A 14 MeV neutron activation analysis system is described that is being used primarily to determine trace levels of oxygen in metals. No sample container is required for relatively inert solid metal samples thus increasing the sensitivity of the method by a factor of five. Under these conditions the sensitivity and precision foroxygen is about 6±3.3 μg in a single determination, resulting from collecting 1.2¹⁶N counts per μg of oxygen. A method is described for calibrating the system for the analyses of large metal samples. The preparation and use of sample containers for the analyses of particulate and/or reactive samples is also presented. Work was performed at the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2567.