Preparation Of Standard Gas Mixtures Research Articles

Trace impurities measurement in ultra-high purity gases and their uncertainties: case study on permanent gas impurities in pure nitrogen

Trace measurement for gas impurities plays an important role in the quality determination of pure-gases. High purity gases will certainly have a higher economic value than gases with lower purity, especially for the ultra-high purity gases used in the preparation of standard gas mixtures. These types of gases shall have a maximum limit for their impurities, which should be verified by a validated method. In this study, an experiment was conducted to determine the impurities in three cylinders of ultra-high purity nitrogen (UHP N2) gases using a validated gas chromatography equipped with pulse dicharge helium ionization detector (GC-PDHID) method. The impurities detected by the GC-PDHID in the aforementioned UHP N2 samples consist of argon (Ar), oxygen (O2), methane (CH4), and carbon monoxide (CO). Meanwhile, hydrogen (H2) and carbon dioxide (CO2) cannot be seen on the chromatogram, then assumed to be lower than the PDHID’s detection limit. Concentrations of the impurities, along with their uncertainties, were found to be 0.987 ± 0.104; 5.818 ± 0.807; 3.163 ± 0.449; and 1.289 ± 0.158 μmol/mol for Ar, O2, CH4, and CO, respectively for the first N2 cylinder. H2and CO2 were estimated to be half of the limit of detection, and H2O component was quoted from the UHP N2 manufacturer’s certificate of analysis. The other two N2 cylinders showed almost similar amounts of impurities. Based on the results, the actual purity for each of the three N2 gases can be estimated as 99.9987% mol/mol; 99.9987% mol/mol; and 99.9988% mol/mol. It is expected that the results of this study could useful as reference for both pure-gas manufacturers and consumers to properly determine the quality of their products.

Electrochemical preparation of standard gas mixtures using solid-state electrolyte membrane

A novel electrochemical method of preparation of standard gas mixtures for calibration of gas-analytical equipment with O2, H2 and CO was elaborated. Utilization of solid state electrolyte membrane allows to perform a nearly 100%-efficient electrochemical generation or conversion of the analyte and avoid some problems typical for liquid electrolytes, such as solvent evaporation and condensation at the inner walls of the gas tubes or deviations from the Faraday’s law. Analysis of uncertainties associated with the calibration procedure showed that the lowest systematic errors are achieved when the calibrant is generated during the electrolysis (i.e. anodic evolution of oxygen or cathodic generation of CO), and the major uncertainties are associated with operation of the flow controllers. For calibration with H2, where the calibrant is partially converted during the electrochemical process, the total uncertainty is essentially determined by molar fractions of the components in H2-Ar mixture, instrumental errors of the equipment, primarily by precision of mass-flow controllers or stability of the gas flow, and the initial flow rate of the calibrant-containing gas mixture. The relative total errors of calibration with oxygen are assessed to be 5–6%; similar uncertainties were calculated for analysis of oxygen content in standard gas mixtures by chromatography using the electrochemical method of calibration.

Methods and Devices for the Preparation of Standard Gas Mixtures

A review of methods for the preparation of standard gas mixtures (SGMs) with the known concentrations of organic and inorganic gases and vapors is presented. The classification of methods is proposed and their advantages and disadvantages are compared. Along with the widely known thermal diffusion and gasextraction methods and devices for the preparation of SGMs functioning on their basis, i.e., sources of gas and vapor microflows and vapor-phase sources of gas mixtures, the review considers and discusses metrological possibilities proposed by Russian researchers of chromatomembrane and chromato-desorption methods of SGM preparation and corresponding instrumentation.

A transfer technique of small amount of gas for the preparation of standard gas mixtures

Standard gas mixtures (SGMs) of trace level in high-pressure cylinder are typically prepared by multi-stage dilution from the pure gases. Here ‘a small amount of gas transfer technique’ was developed to prepare SGMs, in which the number of dilution stages could be much less than typical process. The preparation process and the technique were introduced in detail. And the theory and key points of the technique were discussed. As an example, Freon 12 SGMs of trace level (100nmol/mol) were prepared by the technique through only three-stage dilution, the relative standard uncertainty of preparation was less than 0.2%. The results showed consistency agreement of <0.2%. In order to verify the reliability of the technique a Freon 12 SGMs of 1μmol/mol and 0.1μmol/mol were prepared by conventional method through four-stage and five-stage dilution respectively. The standard uncertainty of Freon 12 prepared by two methods was similar and the result of the consistency of two methods was satisfied. Considering the savings of time and labor, the technique is worth to be recommended.

International comparison CCQM-K66: Impurity analysis of methane

This key comparison was performed to demonstrate the capability of NMIs to analyse the purity of methane for use as a source gas in the preparation of standard gas mixtures. This capability is an essential requirement for the preparation of accurate standards of natural gas and some other fuels.Since it is difficult to carry out a comparison with individual samples of pure gas, the sample for this comparison was a synthetic mixture of high purity methane with selected added impurities of nitrogen, argon, carbon dioxide and ethane. These mixtures were prepared by a gas company as a batch of 10 cylinders and their homogeneity and stability were evaluated by NMIJ.The KCRVs for the four different analytes in this key comparison are based on a consensus of values reported by participants. The uncertainties in the degrees of equivalence were calculated by combining the reported uncertainties with the homogeneity of the samples and the uncertainty of the KCRV. The results submitted are generally consistent with the KCRV within the estimated uncertainties.Finally, this comparison demonstrates that the analysis of nitrogen, argon, carbon dioxide and ethane in methane at amount fractions of 1 µmol/mol to 5 µmol/mol is generally possible with an uncertainty of 5% to 10%.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Study of a method for the preparation of standard gas mixtures based on thermal decomposition of surface compounds. Application to isothiocyanates

Further development of a previously introduced concept for the generation of standard gas mixtures by thermal decomposition of surface-bonded residues is described. The method was applied to isothiocyanates, which are produced as the sole volatile product from silica gel-anchored dithiocarbamate groups.

Gas chromatographic determination of volatile anaesthetic agents in blood. Part 1. Preparation of standard gas mixtures of volatile anaesthetic agents.

A method for preparing standard gas mixtures of the volatile anaesthetics halothane, enflurane and isoflurane is described. Static mixtures of gases of known concentration can be prepared manometrically by measuring the required pressure of anaesthetic gas into a bulb and diluting to atmospheric pressure with air. Standard gas mixtures in the concentration range 0-4% V/V can be prepared with an accuracy of +/- 0.01% V/V, and the relative standard error of measurements of a single standard concentration is less than 0.8%. Significant adsorptive losses in the gas sampling valve were observed for gas standards prepared in the absence of any diluent gas. These losses were not detected for measurements of standards made up to atmospheric pressure in air. A comparison with calibration procedures currently in practice is presented.

Generation of standard gaseous mixtures

Summary Static and dynamic methods for the preparation of standard gas mixtures are discussed. The principles of the design of devices for the generation of gas mixtures and fundamental equations for calculation of the concentration of a component of interest in a mixture are given. Advantages and shortcomings of the methods are also described.

The preparation of standard gas mixtures. A review

The first page of this article is displayed as the abstract.

All-metal automated Toepler pump for laboratory use

An all-metal automated Toepler pump has been developed with improved safety and reliability over the traditional glass pump. New applications cited include the preparation of standard gas mixtures and the transfer of gas for vapor phase reactions.