Simultaneous determination of CFC-11, CFC-12 and CFC-113 in seawater samples using a purge and trap gas-chromatographic system

We have optimized the analytical parameters of a homemade instrument for the simultaneous measurement of the chlorofluorocarbons CCl₂F₂ (CFC-12), CCl₃F (CFC-11) and C₂Cl₃F₃ (CFC-113) in seawater. Seawater samples are flame sealed into 60 ml glass ampoules avoiding any contact with the atmosphere and stored in cold, dark condition until analysis. In the laboratory, after cracking the ampoule in an enclosed chamber filled with ultra-pure nitrogen, the seawater sample is transferred to a stripping chamber, where ultra-pure nitrogen is used to purge the dissolved CFCs from the seawater. The extracted gases are then cryogenically trapped, subsequently the trap is isolated and heated and the CFCs are transferred by a carrier gas stream into a precolumn and then are separated on a gaschromatographic packed column. To separate adequately CFC-12 from N₂O, during the early part of the chromatographic run, the gas stream passes through a molecular sieve, which is then isolated and backflushed. The CFCs are detected on an electron capture detector (⁶³Ni ECD). After a careful choice of the experimental conditions, the performances of the system were evaluated. The detection limits for seawater samples are: 0.0081 pmol kg⁻¹ for CFC-12, 0.0073 pmol kg⁻¹ for CFC-11 and 0.0043 pmol kg⁻¹ for CFC-113. The reproducibility of replicate samples lies within 5% for the three CFCs. The system has been successfully employed for CFC measurements in seawater samples collected in the Ross Sea (Antarctica) in the framework of the Italian Antarctic research project.     

Trends of Atmospheric CCl 3 F,CCl 2 F 2 and CCl 2 FCClF 2 in Shanghai (China)

Atmospheric concentrations of CCl 3 F (CFC-11), CCl 2 F 2 (CFC-12), and CCl 2 FCClF 2 (CFC-113) in troposphere in Shanghai, China (31°1N) have been routinely monitored by using gas chromatography with electron capture detector from November 1997 to December 2000. The observation shows that there is a slowly declining trend of the three compounds. On the other hand, a comparison has been drawn between the concentrations observed and the ones calculated by 2-box model on the basis of the global statistical data of CFCs production and emission. Our observation agrees with the calculations. It shows that production and emission of chlorofluorocarbons (CFCs) in China are still at a low level and gradually decreasing.     

Simultaneous analysis of atmospheric halocarbons and non-methane hydrocarbons using two-dimensional gas chromatography

A gas chromatographic system was constructed to simultaneously measure ambient non-methane hydrocarbons (NMHCs) and halocarbons, which play significant roles in tropospheric ozone formation and stratospheric ozone loss, respectively. A heart-cut device based on a Deans switch was connected to two capillary columns to cover the full range of NMHCs and halocarbons. Analytes more volatile than C₆ NMHCs and the halocarbon CFC-113 were separated with a PLOT column, while the remaining less volatile compounds were separated with a DB-1 column. Merge-and-split of the flows at the end of the two columns allowed the NMHCs and halocarbons to be observed simultaneously by electron capture detection (ECD) and flame ionization detection (FID). To avoid peak-overlap from the two columns while merging, programmed pressures were incorporated to control the Deans switch. In addition to the advantage of measuring two important classes of compounds in the atmosphere at the same time, this method has the additional benefit of using the homogeneity of atmospheric CFC-113 as an “intrinsic” internal reference. Thus, better data continuity, less consumption of gas standards, and real-time quality control can all be achieved.     

A method for carbon stable isotope analysis of methyl halides and chlorofluorocarbons at pptv concentrations

A pre-concentration system has been validated for use with a gas chromatography/mass spectrometry/isotope ratio mass spectrometer (GC/MS/IRMS) to determine ambient air (13)C/(12)C ratios for methyl halides (MeCl and MeBr) and chlorofluorocarbons (CFCs). The isotopic composition of specific compounds can provide useful information on their atmospheric budgets and biogeochemistry that cannot be ascertained from abundance measurements alone. Although pre-concentration systems have been previously used with a GC/MS/IRMS for atmospheric trace gas analysis, this is the first study also to report system validation tests. Validation results indicate that the pre-concentration system and subsequent separation technologies do not significantly alter the stable isotopic ratios of the target methyl halides, CFC-12 (CCl(2)F(2)) and CFC-113 (C(2)Cl(3)F(3)). Significant, but consistent, isotopic shifts of -27.5 per thousand to -25.6 per thousand do occur within the system for CFC-11 (CCl(3)F), although the shift is correctible. The method presented has the capacity to separate these target halocarbons from more than 50 other compounds in ambient air samples. Separation allows for the determination of stable carbon isotope ratios of five of these six target trace atmospheric constituents within ambient air for large volume samples (相似文献   

Influence of free-space calibration using He on the measurement of adsorption isotherms

It is well known that helium (He) molecules that remain inside micropores after free-space calibration at a low temperature (77.4 K) affect the shape of an adsorption isotherm, especially in a very low relative pressure region. This negative effect of the remaining He leads to a misunderstanding of the porous characteristics, such as micropore size distribution and surface properties. However, it is still believed that such erroneous interpretations are limited to narrow microporous materials such as activated carbon and measurements at low temperatures, namely the measurement of the adsorption of N₂ and Ar at their boiling points. Here we report a systematic investigation of the influence of free-space calibration using He on microporous, mesoporous and non-porous materials. Zeolite Y, mesoporous silica, carbon black and aerosil 200 were used for the measurements. N₂, H₂O and CO₂ adsorption isotherms were measured at 77.4, 298 and 298 K, respectively. Free-space calibration was carried out before and after the isotherm measurement for each sample. Although the influence of the He that remained in the sample was small for the non-porous sample, the shape of the isotherms for the other samples in a low relative pressure region was rather affected by the timing of the free-space calibration even for the mesoporous sample, and at an ambient temperature.     

Investigations of CsCl,K2SO4, and K2CrO4 as high temperature calibrants for differential scanning calorimetry

The selection of reference materials having calibration quality data sets is essential to meaningful measurements with DSC. In the present work the results of critical evaluations of the data sets for such materials are reported. New studies for three salt systems, CsCl, K₂SO₄, and K₂CrO₄ as calibrants for high temperature DSC, were undertaken, and are reported. The studies were extended to include Bi and KNO₃, two prospective candidate materials for measurements at lower temperatures, and these results are also reported herewith.     

Redox potential measurement in natural waters

Summary In spite of the importance of the redox potential (Eh) its experimental measurement in natural environment is still not entirely resolved. In the present work an optimization of the methodology to measure Eh is carried out. The behaviour and storing conditions of the standard solutions, the kind of reference electrode, as well as the kind of the working electrode are studied for calibration. From the results it is concluded that Eh measurements must be done in situ. As electrodes, Ag/AgCl electrode with sleeve-type junction and laminar Pt electrode, previously calibrated with Zöbell solution, should be used. A special cell that allows to carry out the measurement of Eh in ground water samples without variations in its composition and characteristics is proposed for in situ measurements. The proposed procedure is applied to Eh measurement of ground water of different chemical composition. Finally, the experimental values of Eh measured in these samples are applied to WATEQF program to know the distribution of the chemical species in these systems. Eh are mainly determined by the reduced forms Fe²⁺ and FeCO₃ and the oxidized forms amorphous Fe(OH)₃ and Fe₂O₃ (maghemite).     

Development of membrane inlet mass spectrometry for examination of fermentation processes

Membrane inlet mass spectrometry (MIMS) is useful for on-line monitoring of fermentation processes. However, readings are affected by the complex and dynamic matrix in which biological processes occur, making MIMS calibration a challenge. In this work, two calibration strategies were evaluated for measurement of typical products of acidogenic fermentation, i.e., ethanol, H₂, and CO₂ in the liquid phase, and H₂ and CO₂ in the gas phase: (1) “standard calibration”, which was performed independent of fermentation experiments with sterile standards in water with a N₂ headspace, and (2) “in-process calibration” whereby fermentation was monitored concurrent with off-line analysis. Fermentation was operated in batch and continuous modes. In-process calibration was shown to be most effective for measurements of H₂ and CO₂ in both gas and liquid phases; standard calibration gave erroneous results. In the gas phase, this was due to a lower sensitivity during experiments compared to the independent standard calibration, believed to be caused by formation of a liquid film on the surface of the probe. In the liquid phase, moving from the standard calibration environment to the fermentation caused the linear relationship between the H₂ concentration and MIMS signal to change in intercept, and the relationship for CO₂ to change in slope, possibly due to dissolved ions, and related non-ideality. For ethanol, standard calibration results were fairly consistent with in-process calibration results. The main limitation with in-process calibration is the potential for a lack of variability in target concentration. This could be addressed by spiking the targeted compound at the end of the experiment. Regardless, MIMS is an ideal instrument for analysing fermentation experiments, due to its ability to measure targeted compounds semi-continuously, and due to a lack of drift over long periods.     

Measuring atmospheric carbon dioxide—the calibration challenge

The measurement of CO₂ in the atmosphere presents a significant metrology and quality assurance challenge. While global trends can be well determined with just a few sampling sites, the plethora of natural processes involved in exchange of CO₂ with the atmosphere makes the identification of those most effective in regulating the long-term atmospheric levels elusive. To unambiguously link particular processes with significant global trends requires continuous monitoring of small spatial and temporal differences in the atmospheric mixing ratio of CO₂ (and related tracers) over the major global CO₂-exchanging regions. Such differences are often comparable in magnitude to the precision of conventional non-dispersive infrared or gas chromatograph analysers, and much smaller than the uncertainty in the link to a primary standard. In general, laboratories cannot currently merge data at high precision and thus achieve adequate global coverage. We describe an improvement in precision (and operating cost) of the conventional infrared analyser technique. Apart from immediate biogeochemical applications, the new system has demonstrated outstanding diagnostic capabilities and revealed a number of unsuspected sources of bias affecting conventional measurement and calibration methods. In addressing these biases, opportunities are created to improve the link between CO₂ measurement and fundamental constants, and to improve the propagation of CO₂ standards to field measurement systems.     

Calibration transfer strategy to compensate for instrumental drift in portable quadrupole mass spectrometers

We report the use of a calibration transfer strategy to correct for drift in the quantitative sensitivity of a portable quadrupole mass spectrometer (QMS) aimed at process monitoring applications. Gas mixtures of CH₄/Ar/C₂H₆/CO₂ were studied with calibration phase measurements made of the pure gases for a univariate analysis and of 40 multi-component mixtures for a multivariate approach. To evaluate calibrations, test set spectra of a CH₄/Ar/C₂H₆/CO₂ gas mixture were recorded bi-weekly over a period of 12 months. As part of the strategy a standard of pure argon was measured during both calibration and test phases so that correction factors could be calculated for each measurement day. It was shown that in the absence of a calibration transfer strategy quantifications of test set spectra could be inaccurate by more than an order of magnitude over 12 months. Furthermore, due to the effects of drift in the sensitivity over the 6 days required to record the training set in the calibration phase it was found that the multivariate analysis quantified test spectra less accurately than the univariate analysis. However, by applying the calibration transfer strategy across all measurements (both calibration and test phases) it was shown that the errors in prediction using the multivariate analysis previously seen after 2 weeks were not observed until approximately 12 months later.     

Effect of variation in argon content of calibration gases on determination of atmospheric carbon dioxide

Carbon dioxide (CO₂) is a greenhouse gas that makes by far the largest contribution to the global warming of the Earth's atmosphere. For the measurements of atmospheric CO₂ a non-dispersive infrared analyzer (NDIR) and gas chromatography are conventionally being used. We explored whether and to what degree argon content can influence the determination of atmospheric CO₂ using the comparison of CO₂ concentrations between the sample gas mixtures with varying Ar amounts at 0 and 18.6 mmol mol⁻¹ and the calibration gas mixtures with Ar at 8.4, 9.1, and 9.3 mmol mol⁻¹. We newly discovered that variation of Ar content in calibration gas mixtures could undermine accuracy for precise and accurate determination of atmospheric CO₂ in background air. The differences in CO₂ concentration due to the variation of Ar content in the calibration gas mixtures were negligible (<±0.03 μmol mol⁻¹) for NDIR systems whereas they noticeably increased (<±1.09 μmol mol⁻¹) especially for the modified GC systems to enhance instrumental sensitivity. We found that the thermal mass flow controller is the main source of the differences although such differences appeared only in the presence of a flow restrictor in GC systems. For reliable monitoring of real atmospheric CO₂ samples, one should use calibration gas mixtures that contain Ar content close to the level (9.332 mmol mol⁻¹) in the ambient air as possible. Practical guidelines were highlighted relating to selection of appropriate analytical approaches for the accurate and precise measurements of atmospheric CO₂. In addition, theoretical implications from the findings were addressed.     

Review on the thickness measurement of ultrathin oxide films by mutual calibration method

Mutual calibration was suggested as a method to determine the absolute thickness of ultrathin oxide films. It was motivated from the large offset values in the reported thicknesses in the Consultative Committee for Amount of Substance (CCQM) pilot study P-38 for the thickness measurement of SiO₂ films on Si(100) and Si(111) substrates in 2004. Large offset values from 0.5 to 1.0 nm were reported in the thicknesses by ellipsometry, X-ray reflectometry (XRR), medium-energy ion scattering spectrometry (MEIS), Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), and transmission electron microscopy (TEM). However, the offset value for the thicknesses by X-ray photoelectron spectroscopy (XPS) was close to zero (−0.013 nm). From these results, the mutual calibration method was reported for the thickness measurement of SiO₂ films on Si(100) by combination of TEM and XPS. The mutual calibration method has been applied for the thickness measurements of hetero oxide films such as Al₂O₃ and HfO₂. Recently, the effect of surface contamination was reported to be critical to the thickness measurement of HfO₂ films by XPS. On the other hand, MEIS was proved to be a powerful zero offset method which is not affected by the surface contamination. As a result, the reference thicknesses in the CCQM pilot study P-190 for the thickness measurement of HfO₂ films on Si(100) substrate were determined by mutual calibration method from the average XRR data and MEIS analysis. Conclusively, the thicknesses of ultrathin oxide films can be traceably certified by mutual calibration method and most thickness measurement methods can be calibrated from the certified thicknesses.     

A flow injection analyser conductometric coupled system for the field analysis of free dissolved CO<Subscript>2</Subscript> and total dissolved inorganic carbon in natural waters

A flow injection analyser coupled with a gas diffusion membrane and a conductometric microdetector was adapted for the field analysis of natural concentrations of free dissolved CO₂ and dissolved inorganic carbon in natural waters and used in a number of field campaigns for marine water monitoring. The dissolved gaseous CO₂ presents naturally, or that generated by acidification of the sample, is separated by diffusion using a hydrophobic semipermeable gas porous membrane, and the permeating gas is incorporated into a stream of deionised water and measured by means of an electrical conductometric microdetector. In order to make the system suitable and easy to use for in-field measurements aboard oceanographic ships, the single components of the analyser were compacted into a robust and easy to use system. The calibration of the system is carried out by using standard solutions of potassium bicarbonate at two concentration ranges. Calibration and sample measurements are carried out inside a temperature-constant chamber at 25 °C and in an inert atmosphere (N₂). The detection and quantification limits of the method, evaluated as 3 and 10 times the standard deviation of a series of measurements of the matrix solution were 2.9 and 9.6 μmol/kg of CO₂, respectively. Data quality for dissolved inorganic carbon was checked with replicate measurements of a certified reference material (A. Dickson, Scripps Institution of Oceanography, University of California, San Diego), both accuracy and repeatability were −3.3% and 10%, respectively. Optimization, performance qualification of the system and its application in various natural water samples are reported and discussed. In the future, the calibration step will be operated automatically in order to improve the analytical performance and the applicability will be increased in the course of experimental surveys carried out both in marine and freshwater ecosystems. Considering the present stage of development of the method, it can only be applied for studying of the carbon cycle in oxic environments.     

Harmonisation Of Ec Air Quality Directives

Abstract

The Environment Institute of the Joint Research Centre in Ispra devotes an important part of its activities to support the Commission of the European Communities in scientific and technical matters. As an example of these activities, a general overview is given of the harmonisation work lead by its Central Laboratory of Air Pollution for the implementation of EC air quality directives in the European Member States. The different stages of a directive's development are reviewed and illustrated with typical examples of harmonisation work recently undertaken.

Preparatory actions for future regulations are illustrated by the recent intercomparison exercise for VOC measurements, realized in view of the coming directive on photo-oxidants.

Quality assurance programmes are developed that are mainly focused on the evaluation of sampling, calibration and measurement techniques in the Member States. Special attention is also paid to the harmonisation of network design. The results of a recent network design campaign realised in Madrid, using passive sampling techniques in combination with mobile measurements, are presented.

An example of the development of scientific and technical progress is given by the intercomparison of primary NO₂ calibration standards, where the reference method of the directive was checked and compared to new standard methods.     

Der globale Kohlenstoffkreislauf im Anthropozän. Betrachtung aus meereschemischer Perspektive

By burning of fossil fuels humankind emits more than 8 billion tons of carbon (Gt C) in the form of CO₂ to the atmosphere. Since the onset of the industrial revolution the cumulative emissions have led to an increase of the atmospheric CO₂ concentration which corresponds to an additional radiative forcing in the atmosphere. Of the three reservoirs which exchange carbon on the time scale of centuries – atmosphere, terrestrial biosphere, and ocean – the ocean is by far the largest. The marine CO₂ system comprises the chemical species HCO₃^–, CO₃^2–, and CO₂(aq). This gives rise to the pH‐buffering nature of seawater as well as its high uptake capacity for anthropogenic CO₂. Four measurement parameters of the marine CO₂ system are available for an accurate analytical characterization. These parameters also provide a means of sensing the role of physical, chemical, and biological drivers for the marine carbon cycle. The marine carbon cycle features major natural processes that exchange carbon with the atmosphere and re‐distribute it throughout the ocean. These are known as “pumps” and driven by physical and biological factors. While the “physical pump” is inevitably enhanced by the oceanic uptake of anthropogenic CO₂, even the sign of the response is currently not clear for the “biological pumps”. A host of potential consequences of global change (temperature rise, ocean carbonation, ocean acidification) have been identified. These are currently studied intensively with respect to their climate sensitivity as well as the climate feedback potential.     

Sulfur evolution from coal combustion in O2/CO2 mixture

O₂/CO₂ coal combustion technology is considered as one of the most promising technologies for CO₂ sequestration due to its economical advantages and technical feasibility. It is significant to study the sulfur transfer behavior of coal in O₂/CO₂ atmosphere for organizing combustion properly and controlling SO₂ emission effectively. To clarify the effect of atmosphere on the sulfur transfer behavior, thermogravimetry coupled with Fourier Transform Infrared (TG-FTIR) system was employed to study the formation behavior of sulfur-containing gas species from Xuzhou bituminous coal pyrolysis in CO₂ atmosphere compared with that in N₂ atmosphere. Also the SO₂ formation behaviors during Xuzhou bituminous coal combustion in O₂/N₂ and O₂/CO₂ atmospheres were investigated. Results show that COS is preferentially formed during the coal pyrolysis process in CO₂ atmosphere rather than in N₂ atmosphere. When temperature is above 1000 K, sulfate in the CO₂ atmosphere begins to decompose due to the reduction effect of CO, which comes from the CO₂ gasification. During coal combustion process, replacing N₂ with CO₂ enhances the SO₂ releasing rate. SO₂ emission increases first and then decreases as O₂ fraction increases in the O₂/CO₂ mixture. XPS result of the ash after combustion indicates that higher O₂ concentration elevates the sulfur retention ability of the mineral matter in the coal.     

Comparison of portable devices for sub-ambient concentration measurements of methane (CH4) and nitrous oxide (N2O) in soil research

ABSTRACT

Production and consumption of methane (CH₄) and nitrous oxide (N₂O) in soils have a strong influence on global greenhouse gases (GHG) budgets. Therefore, it is crucial to precisely measure GHG fluxes at the soil–atmosphere interface. In upland soils, CH₄ and N₂O can be consumed by microbiological processes, and the respective concentrations can be lower than in the atmosphere, demanding highly sensitive gas analysing systems. Traditionally, soil air is sampled in vials and analysed in the laboratory by gas chromatography (GC). During the last decade, different technologies have been developed that allowed to build portable gas analysers that are able to measure sub-ambient gas concentration directly in the field. Here, we compared sub-ambient to ambient CH₄ and N₂O concentration values from four portable devices using different measurement technologies (a portable GHG analyser based on laser absorption spectroscopy [LAS], two portable Fourier transform infrared spectroscopy [FTIR] devices and a field gas analyser using photoacoustic spectroscopy [PAS]) to traditional GC analysis in the laboratory (a GC system equipped with a flame ionisation detector [GC-FID] and an electron capture detector [GC-ECD]). The accuracy and precision of photoacoustic spectroscopy measurements are strongly influenced by the water vapour content and non-target gases in the sampling air. We used an advanced set-up for a widely used PAS analyser enabling N₂O measurements at sub-ambient concentrations with similar precision and accuracy as the GC-ECD system. Measurements of CH₄ and N₂O by FTIR and LAS devices were in good agreement with the GC systems. We conclude that the portable devices are suitable for studies of GHG fluxes in the field. Thanks to their universal and portable character, LAS, PAS and FTIR devices represent useful alternatives to currently used technologies for field studies.     

AFM investigations on the influence of CO2 exposure on Ba0.5Sr0.5Co0.8Fe0.2O3–δ

In this work, fresh and CO₂-exposed specimens of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3–δ (BSCF) are examined by atomic force microscopy (AFM) using amplitude-modulated Kelvin probe force microscopy (KPFM) and also electrostatic force microscopy (EFM) to characterize the early stages of the formation of reaction products due to reaction with gaseous CO₂. A comparison is made with results from electron microscopy on the same samples. BSCF specimens exposed for 24 and 240 h to an atmosphere of 99.9 % CO₂ at 900 °C, respectively, were analyzed and compared with non-exposed specimens. The observation of interconnected carbonate islands on BSCF forming a continuous carbonate layer after some exposure to CO₂ indicates a Stranski–Krastanov or Volmer–Weber growth mechanism of the carbonate layer. Our results demonstrate that the measurement of surface potential variations by means of KPFM and EFM constitutes a very sensitive technique to detect the formation of reaction layers on gas permeation membranes such as BSCF. In contrast to electron microscopy techniques, scanning probe techniques permit the investigation of the topography and of electrochemical characteristics of the sample surface as received and without further preparation.     

Ionization gauge sensitivities of N2, O2, N2O,NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^?1 Pa≤p≤1.3·10^?3Pa. Nitrogen was used as a calibration standard.