Preparation Of Gas Mixtures Research Articles

Optimal preparation of Bose and Fermi atomic gas mixtures of 87Rb and 40K in a crossed optical dipole trap

We report on the optimal production of the Bose and Fermi mixtures with 87Rb and 40K in a crossed optical dipole trap (ODT). We measure the atomic number and lifetime of the mixtures in combination of the spin state |F = 9/2, m F = 9/2〉 of 40K and |1, 1〉 of 87Rb in the ODT, which is larger and longer compared with the combination of the spin state |9/2, 9/2〉 of 40K and |2, 2〉 of 87Rb in the ODT. We observe the atomic numbers of 87Rb and 40K shown in each stage of the sympathetic cooling process while gradually reducing the depth of the optical trap. By optimizing the relative loading time of atomic mixtures in the MOT, we obtain the large atomic number of 40K (∼6 × 106) or the mixtures of atoms with an equal number (∼1.6 × 106) at the end of evaporative cooling in the ODT. We experimentally investigate the evaporative cooling in an enlarged volume of the ODT via adding a third laser beam to the crossed ODT and found that more atoms (8 × 106) and higher degeneracy (T/T F = 0.25) of Fermi gases are obtained. The ultracold atomic gas mixtures pave the way to explore phenomena such as few-body collisions and the Bose–Fermi Hubbard model, as well as for creating ground-state molecules of 87Rb40K.

Gravimetric Preparation of Toluene CGMs in Nitrogen Gas: Verification and Stability Assessment

AbstractThis research paper presents the preparation, verification and stability evaluation of a toluene calibration gas mixtures (CGMs) in nitrogen gas via gravimetric method. These toluene gas mixtures are prepared gravimetrically i. e., by wt. mixing of high‐purity gases according to the International Organization for Standardization, ISO 6142, and are validated as per ISO 6143. Toluene gas mixtures within the range of 5 to 20 μmol/mol are prepared and traceability with SI, ‘International system of units’, amount of substance, the ′mole′, through mass‐based measurements is achieved. The verification of prepared CGMs was carried out using a GC‐FID (gas chromatography with flame ionization detector) technique, and the outcomes demonstrated a consistent linear correlation between instrumental response and gravimetric amount fraction for all gas mixtures, which confirmed the accuracy and reliability of CGMs. The gravimetric uncertainty of the prepared gas mixtures, as projected in terms of amount fractions, is below 1 % relative, while the analytical uncertainty is in the range of 2–3 % relative at a confidence level of k=1. The stability study investigation over a period of one year demonstrated that the mole fraction of toluene remained consistent throughout the entire duration, which indicated the long‐term stability of the CGMs.

Evaluation of Leading Smartwatches for the Detection of Hypoxemia: Comparison to Reference Oximeter.

Although smartwatches are not considered medical devices, experimental validation of their accuracy in detecting hypoxemia is necessary due to their potential use in monitoring conditions manifested by a prolonged decrease in peripheral blood oxygen saturation (SpO2), such as chronic obstructive pulmonary disease, sleep apnea syndrome, and COVID-19, or at high altitudes, e.g., during sport climbing, where the use of finger-sensor-based pulse oximeters may be limited. The aim of this study was to experimentally compare the accuracy of SpO2 measurement of popular smartwatches with a clinically used pulse oximeter according to the requirements of ISO 80601-2-61. Each of the 18 young and healthy participants underwent the experimental assessment three times in randomized order-wearing Apple Watch 8, Samsung Galaxy Watch 5, or Withings ScanWatch-resulting in 54 individual experimental assessments and complete datasets. The accuracy of the SpO2 measurements was compared to that of the Radical-7 (Masimo Corporation, Irvine, CA, USA) during short-term hypoxemia induced by consecutive inhalation of three prepared gas mixtures with reduced oxygen concentrations (14%, 12%, and 10%). All three smartwatch models met the maximum acceptable root-mean-square deviation (≤4%) from the reference measurement at both normal oxygen levels and induced desaturation with SpO2 less than 90%. Apple Watch 8 reached the highest reliability due to its lowest mean bias and root-mean-square deviation, highest Pearson correlation coefficient, and accuracy in detecting hypoxemia. Our findings support the use of smartwatches to reliably detect hypoxemia in situations where the use of standard finger pulse oximeters may be limited.

Comparison of gravimetry and dynamic dilution for the generation of reference gas mixtures of CO2 at atmospheric amount fraction

Carbon dioxide (CO2) is the most important greenhouse gas generated by human activities. Its concentration has been growing in the atmosphere reaching a current annual average of 410 μmol mol−1. Reliable determinations of the atmospheric CO2 concentration are of great importance for the development of models used in climate change predictions. The production of reference mixtures of known composition is a key step for the achievement of reliable data for the monitoring of greenhouse gases in atmosphere.The present work deals with a comparison of two methods for gas mixtures preparation, the first based on the gravimetric preparation of gas mixtures in high pressure cylinders and the second based on dynamic dilution, for generating gas mixtures at the desired amount fraction online.Reference mixtures of CO2 can be used for the calibration of monitoring sensors, with various applications ranging from environmental monitoring to industrial process control.

A new look at the sorption kinetics in reference gas standards

The preparation of calibration gas mixtures in cylinders using the gravimetric method (ISO 6142-1) has enabled the production of a wide range of mixtures down to the pmol/mol level with low uncertainties reaching 0.01% relative and beyond. The gravimetric method has limited use however for reactive components that adsorb on the cylinder wall or valve. For such components the adage ‘what comes in = what comes out’ no longer holds. To quantify gas losses in cylinders due to adsorption on the inner surfaces, two methods are typically used: by comparison against other gas mixture preparation methods (e.g. dynamic methods) or by decanting part of a mixture in an identical cylinder followed by cross-comparison. Here we present a new method to elucidate the sorption dynamics based on the use of isotopes (here 12C-methanol and 13C-methanol isotopes). The amount fraction evolution of both isotopes in gas phase is followed in time using laser spectroscopic methods. This way, the kinetics of desorption (mainly 13C-methanol) and adsorption (12C-methanol) can be followed in time. In this paper we will present the results from a pilot study on methanol mixtures at trace amount fractions prepared in different cylinder materials and treatments.

Impurity Analysis of 5.5 N Nitrogen Gas and Its Impact on the Preparation of Class I Type Calibration Gas Mixtures

AbstractKnowledge of impurities in matrix gas is one of the critical requirements for the preparation of class I type calibration gas mixtures (primary reference gas mixtures, PRGMs) as per ISO 6142‐1. PRGMs are prepared gravimetrically using high‐purity component gas and high‐grade nitrogen, here 99.9995 % (5.5 N) as matrix gas. In this study, quantification of gaseous impurities such as moisture (H2O), methane (CH4), and carbon monoxide (CO) in 5.5 N nitrogen is performed using CRDS (cavity ring down spectroscopy). Carbon dioxide (CO2) and total hydrocarbons (THC) are analyzed using gas chromatography flame ionization detector (GC‐FID), while the determination of nitrogen dioxide (NO2) impurity is conducted colorimetrically using a UV‐Vis spectrophotometer. Total impurities in 5.5 N nitrogen are found to be (2945±21.5) ppb. The impact of utilizing this nitrogen is examined through the stability study of ambient range binary component gas mixtures of CH4 and CO in nitrogen and found that 5.5 N nitrogen can be used as matrix gas for preparing PRGMs of CH4 and CO. However, the component gas impurity present in nitrogen potentially affect the accuracy of gravimetrically prepared gas mixture.

Preparation, Verification and Stability of Calibration Gas Mixture of Benzene in Nitrogen

Preparation, Verification and Stability of Calibration Gas Mixture of Benzene in Nitrogen

Enhanced dilution step and gravimetric preparation uncertainty for low-amount fraction standard gas mixtures using a newly developed automatic weighing system for a mini cylinder

The gravimetric method is widely used to prepare standard gas mixtures in gas cylinders. Several dilution steps are required to prepare a low-amount fraction gas mixture, such as at μmol mol−1 level, using the gravimetric method. We have developed a new automatic weighing system (AWS) that is applicable to a mini cylinder (100 mL or less) to reduce the number of dilution steps. The developed mini-AWS is operated by an automatic cylinder exchange mechanism that is similar to the existing AWS. However, the minimum measurable mass was decreased to measure a small amount of target gas; therefore, the gas mixture can be prepared directly at the μmol mol−1 scale. This study evaluated the fundamental performance of the developed mini-AWS, and we gravimetrically prepared several gas mixtures of nominal 100 μmol mol−1 carbon monoxide (CO) in nitrogen (N2). The uncertainties of prepared gas mixtures were consistent within 0.1% of the relative expanded uncertainty. They were then compared to the standard gas mixture, which was gravimetrically prepared using the existing AWS. The compared results agreed within their expanded uncertainties (k = 2).

Gas chromatograph calibration of gas mixtures using a versatile precision volumetric apparatus

A compact, volumetric apparatus was developed for accurate automated preparation of standard gas and gas-liquid mixtures for gas chromatograph detector calibration, with accuracies comparable to those from gravimetric or Coriolis flow methods. The method developed by the principal author is not an adaptation or extension of any other apparatus or technology, and measurements involve only stepper motor steps, temperature, and pressure ratios. Mixture preparation is accomplished via the displacement of gas between chambers in a highly uniform cylinder, separated by a movable piston. Piston movement, with piston end rods of exactly equal diameter, ensures that there is no change in interior volume, and the volume of gas displaced from the bottom into the top compartment is exactly proportional to the piston travel measured to within 10μm. The apparatus, operation, and previously unpublished measurements on common refinery gas mixtures over large concentration ranges are described in detail. These confirmed the accuracy and versatility of the apparatus and also the principle of no pressure change during mixture preparation, from sensitive pressure measurements. Conservative expanded uncertainties in prepared mixture mole fraction ranged from 0.001 to 0.002 over extended composition ranges. Absolute average deviations for the detector response factor for the mixtures ranged from 0.001 to 0.002. An exact new mathematical solution procedure permits the use of impure "pure" gases without loss of accuracy and can be applied to other procedures for standard gas mixture preparation. An exact expression is listed for determining "pure" gas purity.

Quantitation of hydrogen sulfide reference gas mixtures to provide traceability for indoor air quality monitoring

Accurate measurements for the determination of hydrogen sulfide (H2S) are critical for the compliance with legislation in various industries, including natural gas and environmental sectors such as air pollution monitoring. H2S measurements at ambient level are challenging because H2S tends to adsorb on the internal surfaces of the sample collection devices such as gas cylinders and transfer lines. Prolonged exposure to H2S has known health implications to humans, such as irritation to the nose, throat and airways that results in coughing or inflammation, wheezing and shortness of breath around the chest. H2S is mainly monitored for occupational health and safety and indoor air quality monitoring. It is a highly reactive gas that can easily react with oxygen to form sulfur dioxide (SO2) and with water to form sulfuric acid (H2SO4). The traceability of H2S measurements is achieved through the preparation of reference gas mixtures. These gas mixtures are gravimetrically prepared in accordance with International Organization for Standardization (ISO 6142–1:2015). The H2S reference gas mixtures were produced with the highest metrological capability; thus, the molar mass, purity assessment, and the weighing gave an overall gravimetric relative uncertainty which is less than 0.10% (k = 1). One of the biggest challenges in producing a H2S reference gas mixture is the handling of a gas cylinder from the gravimetric preparation process until the verification stage. This work will detail the improved techniques and measurements used to produce the H2S reference gas mixtures. The internal consistency between the mixtures was verified using a non-dispersive ultraviolet (NDUV) spectroscopy analyzer, an ultraviolet fluorescence spectroscopy (UVFS) analyzer and gas chromatography coupled with a pulsed discharged helium ionization detector (GC-PDHID). Our measurement uncertainty results show that the gravimetric value, internal consistency, adsorption, homogeneity, and stability were within a relative uncertainty of 1.2% as compared to our previous uncertainty of 4.4%. This is a significant improvement for the measurements of H2S reference gas mixtures.

DEVELOPMENT OF CALIBRATION GAS MIXTURES (CARBON DIOXIDE AND OXYGEN IN NITROGEN MATRIX) AT A TYPICAL CONCENTRATION RANGE OF MODIFIED ATMOSPHERE PACKAGING

Measurement of carbon dioxide (CO2), oxygen (O2), and nitrogen (N2) concentration in modified atmosphere packaging (MAP) food is critical to be carried out by the food industry. A slight variation in concentrations of CO2, O2, and N2 in food packaging may have a significant impact on product quality and safety for human health. Accurate and reliable measurement of CO2, O2, and N2 concentrations in food packaging is crucial, and it can only be achieved by calibrating the gas analyzer. This study aimed to develop gas mixtures for the calibration of CO2, O2, and N2 gas analyzers at a typical concentration range of modified atmosphere packaging. The calibration gas mixtures were prepared gravimetrically by following ISO 6142. The concentration ranges of CO2, O2, and N2 for calibration gas mixtures were set at 9-19% mol/mol, 1-5% mol/mol, and 74-88% mol/mol, respectively. Each parent gas was identified for its impurities using gas chromatography with a pulsed discharge helium ionization detector (GC-PDHID). The compositions of CO2, O2, and N2 in the mixtures were verified by evaluating the internal consistency within the prepared gas mixtures using gas chromatography with a thermal conductivity detector (GC-TCD). The short term stability of the prepared gas mixtures was evaluated using an equal division method. The result showed that good internal consistency was achieved between the gravimetrical and GC’s verification values, having linear regression coefficient (R2) ≥ 0.999. The t-test result has shown that CO2 has better short term stability than O2 and N2. In conclusion, the developed calibration gas mixtures at a typical concentration range of modified atmosphere packaging have shown satisfying results for CO2 component. However, further evaluation is still required to minimize the instability of O2 and N2 components.

A simple method for the preparation and injection of gas mixtures into a gas chromatograph using a two-component device

Environmental sciences are expanding and are based on standardized and certified calibrations when measurements are required. When a gaseous composition is quantified, commercial standards are used. Here, we report on a two-component device for the preparation and injection of gas mixtures at the appropriate levels of pressure and volume. The two-component calibrator/injector can be used simultaneously or separately depending on the experimental objective but their combination is extremely effective for injecting gas mixtures at low concentrations. The quantity of gas introduced into a gas chromatograph with the injector can be adapted to the sensitivity of the detector or to avoid column overload. The calibrator provides for a large range of gas-mixture concentrations, from ppm to % mol/mol with an error of preparation of around 1% and an accuracy of less than 3%. This device prepares a variety of gas mixtures (hydrogen, methane and dioxide of carbon) which are compared with certified mixtures by means of gas chromatographic measurements. The results show good agreement between prepared and certified mixtures with a maximum difference of 2% which remains within the relative error of commercial standard. In addition, the preparation of dissolved methane at different concentrations in seawater is presented as a direct application of the calibrator.

A new implementation of EN1839 method T mixture preparation to prepare calibration gas mixtures for anesthetic gas monitors.

In this study different mixtures from anesthetic liquids vapours in air and O2-sevoflurane/air, sevoflurane/O2 and isoflurane/O2-were prepared according to EN1839 method T. The gases mixtures were used to calibrate anesthetic gas monitors. The targeted concentrations (TCs) from sevoflurane and isoflurane in air and O2 were 0 vol%, 0.15 vol%, 0.7 vol%, 1 vol%, 1.5 vol%, 2.5 vol%, 5 vol%, 6 vol% and 8 vol%. The values of liquids, air and O2 flow rates which are corresponding theoretically to the TCs were calculated. The results showed that the measured concentrations by anesthetic gas monitor are in good agreement with TCs. Full validation was performed to assure the suitability of the method for preparing gas mixtures to calibrate anesthetic gas monitors. Linearity, limit of detection (LOD), limit of quantification (LOQ), precision, method robustness and uncertainty of measurement results were evaluated in the validation study. The results indicated that the method is valid for the purpose of analysis.

Control of a Detonation Wave in a Channel with Obstacles Using Preliminary Gas Mixture Preparation

Using the detailed kinetic mechanism of chemical interaction, the effect of preliminary preparation of the stoichiometric hydrogen-air mixture (dissociation of a part of molecular hydrogen and oxygen on atomic gases) on the detonation wave characteristics is investigated numerically with the aim to control detonation combustion in plane channels with obstacles. It is found that the above-mentioned partial initial dissociation can be used to prevent quenching of detonation in channels with both a single obstacle and multiple barriers. It is revealed that the mixture, obtained as a result of preparation, differs from the initial hydrogen-air mixture by the qualitatively different type of detonation re-initiation after interaction with obstacles.

Reference Gas Mixtures of Formaldehyde in Nitrogen: Preparation by a Dynamic Gravimetric Method

The preparation of formaldehyde gas mixtures required for metrological assurance of air pollution control is an urgent task. Methods for the preparation of gas mixtures of formaldehyde for metrological purposes are considered. The 2 μmol/mol-level gas mixtures of formaldehyde in nitrogen have been obtained by a dynamic-gravimetric method with the depolymerization of trioxane vapor. The efficiency of the trioxane conversion process was experimentally studied. The sources of uncertainty are analyzed in detail. The reference gas mixtures obtained were used for the formaldehyde mole fraction measurements during the CCQM-K90 key comparison. The relative expanded uncertainty of the measurement U = 3.3% was achieved, confi rmed by the comparison results.

Dynamic calibration method for reactive gases

In this study an evaporation method is applied to dynamically generate reference gas mixtures with an accurately known concentration of reactive compounds. As a representative application, the method is used to generate several reference gas mixtures for oxidized mercury. The reliability of online monitoring of gases is dependent on the availability of accurate and metrologically traceable calibration standards. For reactive gases this is a challenge since these sticky gases easily adsorb to surfaces, which complicates and can even prevent the use of traditional static tools. In the evaporation method, a solution with well-known concentration is dosed using, e.g. an automatic syringe pump or a peristaltic pump, and mixed with the carrier gas flow. Mixing and evaporation are key parts of this process, along with temperatures and materials in different parts of the system and gas flow rate, which play an important role in the response time optimization. To estimate the applicability of this method we test its operation in the case of oxidized mercury by investigating the key operational parameters: calibrator response time and stability, possible non-linear behaviour of selected molecules, and also sensitivity to interference caused by other reactive gas compounds. We also compare its outcome to a traceable source for Hg0. Based on the achieved results the evaporation method technique is both a potential and feasible tool for the dynamic preparation of calibration gas mixtures for reactive components, in both laboratory and field conditions.

Experimental Installation used for Preparation of Breathing Mixtures Needed for Professional Diving

Starting from the mathematical modelling of the gas dynamics processes and, of course, from the needs of the Diving Center, several schemes of experimental installations were developed. These schemes are used for the preparation of binary or ternary gas mixtures, specific: for autonomous professional diving, for the system diving, respectively for those simulated or real which are performed in the hyperbaric chambers of the Diving Center or in the diving turrets.The principle of preparing breathing gas mixtures in the experimental installation ensures that an invariable flow rate (with the pressure of the gaseous mixture from a pressurized cylinder) is injected (constant mass flow) while ensuring the permanent control of this flow. The installation delivers an invariable gas mixture flow regardless of the gas pressure value inside the storage cylinder.Depending on the number of components from which the binary or ternary breathable mixture is to be prepared, the design of the plant has been structured in two parts or in the case of a more complex ternary structure of the gaseous mixture, the plant has three distribution-injection lines active. Each of these lines independently carries the three pure component gases used to continuously produce the required respiratory mixture.Finally, the tests of the gas-dynamical processes related to the plant were presented very succinctly, following a comprehensive testing and evaluation plan in the summer of last year.

Redefinition of the mole and uncertainty of analytical measurements

Redefinition of the basic units of the International System of Units (SI) — the kilogram, mole, ampere, and kelvin, — which are now expressed in terms of fundamental physical constants means a substantial revision of the system. In particular, the new definition of the mole fixing the value of the Avogadro constant sets a unit of the amount of substance, which is independent of the unit of mass. We consider some consequences of redefining (the mole and kilogram) and focus on the uncertainty of measuring the amount of substance and related quantities which are important for description of the mixture composition. The issue regarding the molar mass of the substance and associated uncertainty is considered in detail It is noted that calculation of the molar mass using relative atomic masses, involves the molar mass constant which is not equal exactly to 1 g/'mol in the new SI. This introduces an additional, though very small, uncertainty of less than 1 x 10-9in relative terms. The budget of uncertainty for the amount of substance determined through the mass measurements when the mass is measured with the highest accuracy is scrutinized. It is demonstrated that for substances of less than 99.98% purity, the uncertainty associated to the purity is comparable to that of relative atomic masses of the elements. For high-purity substances, the uncertainty in the relative atomic masses have the largest contribution to the budget. Anyhow, the uncertainty associated to the molar mass constant is three orders of magnitude less than the nearest contribution to the uncertainty attributed to weighing. In the case of derived quantities which are the ratio of two quantities of the same kind, the additional uncertainty does not arise at all. This is illustrated by the calculation of the mole fraction of a component in the gravimetrically prepared gas mixture.

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.