共查询到20条相似文献,搜索用时 0 毫秒
1.
M. Sega Margherita Plassa Elena Amico di Meane 《Accreditation and quality assurance》2001,6(7):306-309
In routine chemical measurements traceability can be achieved by using analytical instruments calibrated against primary reference
materials. In the present work the calibration of a CO2 non-dispersive infrared (NDIR) analyzer with measuring range 0–2000 μmol/mol of CO2 and a resolution of 5 μmol/mol is reported. A procedure with working reference gas mixtures (WRMs) has been adopted, which
requires seven calibration points. Primary reference gas mixtures (PRMs) are used to validate WRMs in a narrower range around
the average atmospheric CO2 concentration value. In this range the relative uncertainty reached is of the order of some parts in 103 and the corrections are between 1 μmol/mol and 5 μmol/mol.
Received: 16 March 2000 Accepted: 27 November 2000 相似文献
2.
D. S. Robertson 《Speculations in Science and Technology》1998,21(3):171-185
It has been established from geological studies that change in the atmospheric content of carbon dioxide gas commenced about one hundred million years ago. The likely origin of this change is advanced as being the onset of the Brewer circulation caused by the rise in terrain induced by tectonic plate movement. It is demonstrated that tectonic plate movement can be affected by impacts from external bodies which penetrate the crust of the Earth. The consequences of the change in atmospheric concentration of carbon dioxide are proposed as first, extinctions and reductions in animal numbers, including primates, as a result of changes in body chemistry of these animals and second, a change in the rate of weathering of rocks giving rise to changes in the availability of chemicals such as calcium and potassium which are essential for plant and animal life. This latter change contributing to the extinctions and reductions in animal numbers. It is shown that the change in weathering can account for the rise to dominance of angiosperm plants. It is concluded that there were several simultaneous evolutionary environments on Earth which were a function of altitude which gave rise to a vertical variation in atmospheric content of carbon dioxide. This variation disappeared with rise of terrain and the onset of the Brewer circulation. Such changes are advanced and being much more important than any changes in temperature caused by greenhouse effects since the disappearance of atmospheric variations in carbon dioxide allowed animal migration. It is demonstrated that the conditions of extinction could be reintroduced by human activities. 相似文献
3.
A method was proposed for the direct determination of carbon dioxide in air using a sorption tube specially constructed for this purpose. The method is based on measuring the volume of air consumed for the neutralization of a known amount of barium oxide hydrate in the tube by carbon dioxide contained in air. The equivalence point is detected by the minimum electrical conductance of the barium hydroxide solution. To verify the accuracy of the method, a technique based on the use of a calibration mixture of air with the CO2 concentration varying by the inverse exponential law was developed. The method is suitable for the determination of CO2 in air in a wide concentration range and for the verification and calibration of indirect methods for the determination of CO2. With an insignificant decrease in accuracy, the equivalence point can be detected by the change in the color of phenolphthalein. This significantly simplifies the method and allows its wide use in practice, e.g., in laboratory works in environmental science or for demonstration purposes in educational organizations. 相似文献
4.
An efficient and convenient synthesis of ethylene carbonates was achieved by the reaction of carbon dioxide with 1,2-diols in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), followed by treatment with 1-bromobutane. This DBU-promoted transformation proceeded at an atmospheric pressure of carbon dioxide at 25 °C and gave ethylene carbonates in good yields. 相似文献
5.
Atsushi SudoYosuke Morioka Eri KoizumiFumio Sanda Takeshi Endo 《Tetrahedron letters》2003,44(43):7889-7891
Cycloaddition of aziridine with carbon dioxide was successfully catalyzed by alkali metal halide or tetraalkylammonium halide to give the corresponding 5-membered cyclic urethane, 1,3-oxazolidin-2-one, selectively. The reaction can be performed at ambient temperature under atmospheric pressure. Analoguous reaction of aziridine with carbon disulfide also successfully gave the corresponding 5-membered cyclic dithiourethane, 1,3-thioxazolidine-2-thione. 相似文献
6.
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. 相似文献
7.
8.
The measurement uncertainty of the result of chemical oxygen demand determination in wastewater was evaluated. The major
sources of uncertainty of the result of measurement were identified as the purity of reagents, volumetric operations, gravimetric
operations, bias, and the repeatability of the method. Identification and evaluation of uncertainty sources was followed by
combined uncertainty calculations. The combined uncertainty was compared to the experimentally determined variation and good
agreement was found, indicating that the major uncertainty sources had been identified. The results show that the major sources
of uncertainty arose from repeatability at high concentration level and volumetric steps at low concentration level, thus
revealing the target operations for reducing the measurement uncertainty of this determination.
Received: 5 August 2002 Accepted: 5 November 2002
Acknowledgements This research was supported by the Ministry of Education, Science and Sport of the Republic of Slovenia (Project Z2–3530).
Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials
in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia
Correspondence to A. Drolc 相似文献
9.
Mary-Grace C. Danao Shih-Fang Chen Richard S. Gates 《Accreditation and quality assurance》2014,19(6):415-422
Exhaled breath (EB) contains volatile and nonvolatile compounds that are correlated with physiological processes in the body, and these breath biomarkers hold enormous diagnostic potential when they are adequately measured and monitored. Thus, the development of instrumentation, including enzyme-based biosensors, for breath monitoring applications has been expanding rapidly. In this paper, the process of estimating the overall combined uncertainty in predicting ethanol concentration, u(C v)pred, using a calibrated alcohol oxidase-based amperometric biosensor is presented. Components that contributed to u(C v)pred were the standard uncertainties associated with simulation of a breath sample with trace ethanol concentration, sampling temperature, biosensor instrumentation, and regression analysis. In both EB and exhaled breath condensate (EBC) sensing, the largest contributor to overall uncertainty was the random effects captured by the regression model at 38.2 % and 39.8 %, respectively, for EB and EBC. This was followed by biosensor instrumentation (34.5 %) and simulation (25.3 %) in EB sensing. The trend was reversed in EBC sensing with EB simulation having a larger contribution (33.8 %) than biosensor instrumentation (25.5 %) owing to a better repeatability of amperometric measurements with aqueous samples. The remaining 2.0 % and 0.9 % were due to breath sampling temperatures in EB and EBC sensing, respectively. This study provides a framework for how to incorporate uncertainty estimation in both breath monitoring and is applicable to biosensing of other breath biomarkers. 相似文献
10.
11.
Kim YJ Kim MI Yun CH Chang JY Park CR Inagaki M 《Journal of colloid and interface science》2004,274(2):555-562
The effect of CO(2) atmosphere on the chemical structure changes of resol-type phenol-formaldehyde spheres during pyrolysis was investigated, in comparison with that of N(2) atmosphere, using FT-IR, TGA, and elemental analysis techniques. It was found that, in contrast to the expectation that CO(2) may act as an oxidizing agent at high temperature, it behaves very similar to N(2) during pyrolysis of PF spheres up to 700 degree C, but results in a somewhat different extent of some specific reactions. That is, although the reactions occurring up to 700 degree C were dominated by crosslinking and/or polyaromatization under both CO(2) and N(2) atmospheres, fewer alkyl-phenolic ether bonds were formed under CO(2) than under N(2). As a consequence, the samples carbonized under CO(2) at 700 degree C were found to have more pendant groups on the edge carbon atoms of carbon in the carbonized samples than those prepared under N(2) atmosphere. 相似文献
12.
《Fluid Phase Equilibria》2002,200(1):19-30
The solubility of nitrous oxide and carbon dioxide in liquid oxygen at temperatures between 90 and 110 K has been measured using a static-analytic method. The NRTL model has been used to calculate the liquid-phase activity. The overall experimental data-set is compared both with the results of the model and with experimental data available in literature. 相似文献
13.
Cantrell W Kostinski A Szedlak A Johnson A 《The journal of physical chemistry. A》2011,115(23):5729-5734
Unlike reversible phase transitions, the amount of heat released upon freezing of a metastable supercooled liquid depends on the degree of supercooling. Although terrestrial supercooled water is ubiquitous and has implications for cloud dynamics and nucleation, measurements of its heat of freezing are scarce. We have performed calorimetric measurements of the heat released by freezing water at atmospheric pressure as a function of supercooling. Our measurements show that the heat of freezing can be considerably below one predicted from a reversible hydrostatic process. Our measurements also indicate that the state of the resulting ice is not fully specified by the final pressure and temperature; the ice is likely to be strained on a variety of scales, implying a higher vapor pressure. This would reduce the vapor gradient between supercooled water and ice in mixed phase atmospheric clouds. 相似文献
14.
Buckley BR Patel AP Wijayantha KG 《Chemical communications (Cambridge, England)》2011,47(43):11888-11890
The use of CO(2) for the preparation of value-added compounds has dramatically increased due to increased global warming concerns. We herein report an electrochemical cell containing a copper cathode and a magnesium anode that effectively converts epoxides and carbon dioxide to cyclic carbonates under mild electrochemical conditions at atmospheric pressure. 相似文献
15.
L. N. Nikitin M. O. Gallyamov E. E. Said-Galiev A. R. Khokhlov V. M. Buznik 《Russian Journal of General Chemistry》2009,79(3):578-588
The application of supercritical carbon dioxide for deposition of fluoropolymer coatings on various substrates and formation of superhydrophobic surfaces and composite core-shell microparticles was discussed. 相似文献
16.
The titrimetric barium carbonate method for the determination of. carbon in organic compounds has been examined and the various sources of error are discussed. The carbon dioxide from the combustion of the sample is absorbed in excess baryta containing 20% (w/v) barium chloride and the excess is back-titrated with hydrochloric acid in the presence of o-cresolphthalein indicator.The value of this method in conjunction with the previously described determination of water with succinyl chloride, for the simultaneous determination of carbon and hydrogen is assessed 相似文献
17.
N-Tosylaziridine was found to be a useful substrate for cycloaddition reaction with carbon dioxide. The reaction was successfully catalyzed by lithium bromide under atmospheric pressure to give the corresponding five-membered cyclic urethane, N-tosyl-1,3-oxazolidin-2-one, selectively. It was found that electron-donating nature of the substituent at 2-position of N-tosylaziridine accelerated the reaction, and this tendency allowed us to estimate the reaction mechanism. 相似文献
18.
Consistent treatment of measurement bias, including the question of whether or not to correct for bias, is essential for the comparability of measurement results. The case for correcting for bias is discussed, and it is shown that instances in which bias is known or suspected, but in which a specific correction cannot be justified, are comparatively common. The ISO Guide to the Expression of Uncertainty in Measurement does not provide well for this situation. It is concluded that there is a need for guidance on handling cases of uncorrected bias. Several different published approaches to the treatment of uncorrected bias and its uncertainty are critically reviewed with regard to coverage probability and simplicity of execution. On the basis of current studies, and taking into account testing laboratory needs for a simple and consistent approach with a symmetric uncertainty interval, we conclude that for most cases with large degrees of freedom, linear addition of a bias term adjusted for exact coverage ("U(e)") as described by Synek is to be preferred. This approach does, however, become more complex if degrees of freedom are low. For modest bias and low degrees of freedom, summation of bias, bias uncertainty and observed value uncertainty in quadrature ("RSSu") provides a similar interval and is simpler to adapt to reduced degrees of freedom, at the cost of a more restricted range of application if accurate coverage is desired. 相似文献
19.
Sihang Qiu Bin Chen Zhengqiu Zhu Yuan Wang Xiaogang Qiu 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(1):165-178
The focus of this paper is locating and quantifying the diffusion source of 137Cs by using observation data collected from monitoring stations. The estimation method is firstly tested in synthetic experiments and then verified with real 137Cs concentration data of Fukushima accident. An atmospheric dispersion simulation system is used to support particle diffusion model. Besides, ridge regression is applied to calculate release rate. In terms of location estimation, posterior function of the source location can be deduced according to Bayesian inference. particle swarm optimization (PSO) method is implemented to locate diffusion source. 相似文献
20.
A method is proposed for the simultaneous determiantion of carbon dioxide and sulphur dioxide in complex matrices. The method involves preseparation of the analysis with a flow-through gas-diffusion unit. The analytes are sensed by two detectors in series, a potentiometric detector responsive to both analytes and a photometric detector for SO2 (p-rosaniline—formadehyde method). The usefulness of the method was tested by applying it to samples of fruity wines and the results were compared with those obtained with the standard EEC recommended method. The reproducibility was generally 7% or better, with a sampling frequency of about 25 h-1. 相似文献