Calibration Gas Research Articles

Portable temperature-controlled permeation device for the generation of formaldehyde gas standard

Formaldehyde is a major indoor air pollutant. Accurate analysis of airborne formaldehyde is essential for effective monitoring and risk assessment. For many formaldehyde analysis techniques, the accuracy of the results depends on the calibration system. Existing formaldehyde calibration methods often face limitations, such as instability over time or limited concentration range. They also lack practicality for on-field calibration either because of bulkiness or because of high gas consumption. To address these challenges, a device using a paraformaldehyde permeation tube within a custom-built, temperature-controlled system was designed and evaluated.The device weighs less than 3 kg and operates using a nitrogen source. Its low gas consumption (30–100 mL min−1) enables the use of a portable gas cylinder of pure nitrogen (<2 kg) as gas supply. Formaldehyde concentrations ranging from 8.3 to 464 µg/m−3 were successfully generated, demonstrating the device’s versatility. A custom-built high-emission permeation tube could generate concentrations from 5 940 to 49 471 µg/m−3 using the same system. Additionally, the emission rate is independent of the flow rate and follows Antoine’s law with respect to temperature, enabling accurate prediction of concentration in various conditions over the evaluated range and beyond. Furthermore, the study confirms the long-term stability (1 year) of the low-emission paraformaldehyde permeation tube, with emission rates remaining mostly within ± 5 % of the average value for each temperature.The temperature-controlled permeation system approach enabled rapid stabilisation of formaldehyde generation at various concentrations and low flow rates, eliminating the need for additional dilution equipment and facilitating on-site instrument calibration at various gas concentrations. This reliable and efficient portable formaldehyde generator offers a valuable solution for field calibration, providing accurate and stable reference gas for diverse analytical needs.

Quantitative analysis of temporal stability and instrument performance during field experiments of an airborne QCLAS via Allan–Werle-plots

Allan–Werle-plots are an established tool in infrared absorption spectroscopy to quantify temporal stability, maximum integration time and best achievable precision of a measurement instrument. In field measurements aboard a moving platform, however, long integration times reduce time resolution and smooth atmospheric variability. A high accuracy and time resolution are necessary as well as an appropriate estimate of the measurement uncertainty. In this study, Allan-Werle-plots of calibration gas measurements are studied to analyze the temporal characteristics of a Quantum Cascade Laser Absorption Spectrometer (QCLAS) instrument for airborne operation. Via least-squares fitting the individual noise contributions can be quantified and different dominant regimes can be identified. Through simulation of data according to the characteristics from the Allan-Werle-plot, the effects of selected intervals between in-flight calibrations can be analyzed. An interval of 30\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$30\\,$$\\end{document}min is found sufficient for successful drift correction during ground operation. The linear interpolation of the sensitivity increases the accuracy and lowers the measurement uncertainty from 1.1%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.1\\,\\%$$\\end{document} to 0.2%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.2\\,\\%$$\\end{document}. Airborne operation yields similar results during segments of stable flight but suffers from additional flicker and sinusoidal contributions. Simulations verify an appropriate interval of 30\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$30\\,$$\\end{document}min in airborne operation. The expected airborne measurement uncertainty is 2.45 ppbv.

In-flight characterization of a compact airborne quantum cascade laser absorption spectrometer

Abstract. Here, we report on the development of a new quantum cascade laser infrared absorption spectroscopy (QLAS) instrument, the Airborne Tropospheric Tracer In-situ Laser Absorption spectrometer (ATTILA), for atmospheric trace-gas measurements on board of the German High-Altitude Long-range Observatory (HALO) aircraft. Its small and light design makes it suitable for airborne measurements up to approximately 150 hPa of ambient pressure (13–14 km). The dual laser instrument can measure several trace gases simultaneously in two 36.4 m path astigmatic Herriott cells with a data acquisition frequency of 1 Hz. We describe the measurement method and the data acquisition of ATTILA and its in-flight performance by focusing on potential sources of influences on the signal, which we investigated with a dedicated test flight during which the instrument sampled from a constant source. We show that linear critical influences associated with challenging movement patterns can be corrected afterwards, while nonlinear limitations can be minimized by appropriate calibration frequencies and integrated time intervals. During the recent aircraft campaign CAFE Brazil (Chemistry of the Atmosphere Field Experiment in Brazil) from December 2022 to January 2023, carbon monoxide (CO) measurements from ATTILA show a good agreement of a R2 of 0.89 with simultaneous CO measurements from an established IR spectrometer for airborne measurements, the TRacer In Situ TDLAS (tunable diode laser absorption spectroscopy) for Atmospheric Research (TRISTAR), at a 10 s time resolution. First dynamical characteristics and tracer distributions of CO and methane (CH4) over the Amazon rainforest can be identified with ATTILA measurements with a total measurement uncertainty of 10.1 % and 17.5 % for calibration gas mixing ratios of 153 and 1990 ppbv and a data accuracy of 0.3 % and 5.5 % for a data acquisition frequency of 1 Hz for CO and CH4, respectively.

Carbon capture, carbon storage and utilization

This aspect of Energy law prompts the Department of Energy to initiate a series of research and development endeavors aimed at assessing environmental suitability and safety, capacity. Additionally, it explores proposed geological storage sites. High-purity carbon dioxide finds primary application in the electronics sector, medical research, and clinical diagnostics. It serves as a calibration gas for carbon dioxide lasers, testing devices, and various mixed gases, besides being a regular component in polyethylene polymerization. The objective of this article is to shed light on theories that model the movement of stored carbon dioxide, aiding in the interpretation and anticipation of chemical alterations and the potential impact of increased pressure.

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.

Compensation of composition variation-induced sensitivity changes in gas phase photoacoustics

Infrared photoacoustic (PA) spectroscopy is a widely used technique to monitor trace gas concentration changes during industrial processes where the bulk composition may vary considerably. However, the PA signal is prone to changes in bulk composition, leading to relative uncertainties in measurements of up to 10%, due to the complex dependence of the sensitivity of a PA system (S) on the thermal and acoustic properties of the gas sample. A novel calibration and concentration calculation method is proposed to keep the relative accuracy of the PA measurements in the few percentages range even in case of large-scale composition variations. The main novelty of the proposed method is that it tackles the complex dependence of the PA system's sensitivity in a way that while it varies the resonance frequency of the calibration gas, it keeps the heat capacity ratio of calibration gases at a constant value. We prove that it determines the analyte’s concentration with relative accuracy of about 1 %, even when the composition of the gas varies drastically. It rigorously compensates for the frequency and heat capacity ratio dependence of S and for the dependence of the half-width of the resonance curve of the PA cell on the thermal and acoustic properties of the gas. Although the reported demonstration measurements are executed in a relatively simple gas mixture, the proposed method has widespread applicability in high-precision monitoring.

Calibration of gas analysis devices with open cuvette

Gas analysis devices are measuring instruments and require periodic confirmation of their metrological parameters. This paper deals with methods of metrological support of measurements of absorption remote devices (with open cuvette). The design of the device where the operating and calibration cuvettes (with calibration gas mixture) are alternately (if necessary) placed on the optical path of the device, with the same optical elements. is proposed. This method of calibration and verification allows you to do without the use of CGM, which greatly simplifies calibration and verification of the gas analyzer at the workplace. In addition, the method reduces the calibration and verification error, since in the calibration mode the light flux passes along the same optical path as in the measurement mode, while the light flux and the degree of contamination of the optical elements by selective and non-selective components of the analyzed mixture remain unchanged.

TYPOMORPHISM OF THE CHEMICAL COMPOSITION OF BIOGENIC CARBONATES WITHIN THE PRADNIPROV METHANE ANOMALY ON THE BLACK SEA SHELF

Problem Statement and Purpose. The aim of the article is to study the typomorphism of the chemical composition of biogenic calcium carbonates within methane anomalies formed by deep fluids in the bottom sediments of the Black Sea shelf. Gas chromatography was performed at the «Pradniprovska» study area. The results of the site`s bottom sediments analysis confirmed the content of pure methane and its homologues in the samples. Due to the presence of methane homologues, oxygen and carbon isotope analysis of the sediment shells was performed (it is known that the most stable information about the chemical composition of the mineral formation environment can be stored in biogenic carbonates of benthic organisms’ shells). The values obtained from the analysis had a small spread and did not show any visible variability. Data &amp; Methods. Data on the chemical composition of benthic organisms’ shells can be obtained using inductively coupled plasma atomic emission spectrometry. This method requires large samples by weight, so only the shells of the Mytilus mollusks were taken for the study due to their relatively large size. The gas-geochemical studies were based on the methodology of the NDL‑3 laboratory. The extracted gas was stored in glass tubes under a saturated saline solution, which ensured minimal losses from gas dissolution in the seal fluid, followed by studying it using a «Tsvet‑400» gas chromatograph. The separation of hydrocarbon gases was carried out on a chromatographic column filled with aluminum oxide. The detector is flame ionization. Calibration was carried out before the start of each cycle with calibration gas mixtures of standard composition. The spectrometric analysis was performed on a Thermo Scientific inductively coupled plasma atomic emission spectrometer with a CID or CMOS detector operating in the range of 167–820 nm. The method is based on the dissolution of substances in a mixture of nitric, hydrochloric and hydrofluoric acids at a temperature of at least 125 °C, followed by the determination of elements in solutions by inductively coupled plasma atomic emission. To consider matrix effects and improve measurement accuracy, calibration using internal standard lines is used. Results. The analysis of the obtained material allowed the author to draw the following conclusions: a) chemical elements in shells are unevenly distributed, and this unevenness is determined by two main reasons – the peculiarity of the formation of biogenic carbonate of shells and the ability of the carbonate to isomorphically capture a number of elements from the mineral-forming environment; b) according to the quantitative characteristics, three groups of elements can be distinguished: macroelements, mesoelements and trace elements. The first group of elements (macroelements) includes Na, S, Mg, Sr, Fe, Si, Mn, P, K. Among them, one can clearly distinguish elements that are isomorphically included in the structure of calcite or aragonite (Na, Mg, Sr, Fe, Mn, K) and elements captured as non-structural impurities in the agglutination process during the growth of biogenic carbonate (Si, S and P). The second group (mesoelements) includes Ba, Al, As, Zn, Cu, Ti, among which two groups can also be distinguished. One is associated with the formation of sulfide minerals paragenetic to biogenic calcite (As, Zn, Cu), and the other with agglutination of clay minerals in sediments (Al, Ti), or a feature of isomorphism in the biogenic formation of calcium carbonate (Ba). The third group (trace elements) is associated with elements of low content and uneven distribution (Ni, Mo, Pb, Se). The main group here is Ni, Cr, Co, V. These groups, taking into account the fact that they were found in the areas of penetration of deep-sea fluids into the sedimentary strata, allows to consider them as typomorphic signs of biogenic carbonate formation in the areas of fluid influence, and, consequently, as a search sign of such areas on the Black Sea shelf.

Highly precise and stabilized measurement system for long-term oxygen measurement at atmospheric concentration level

We developed a high-precision oxygen measurement system with long-term stability using a magneto-pneumatic oxygen analyzer for atmospheric observations. A high precision of 1.4 per meg (which is less than the Network compatibility goal of the Global Atmosphere Watch programme of the World Meteorological Organization) was achieved in a 12-day continuous measurement by maintaining the sample-gas pressure and temperature constant, and by correcting the measured values using a predetermined temperature correction factor. The oxygen measurement system does not require a control gas to compensate for signal drift. The calibration cycle was evaluated to be one week based on the Allan standard deviation. This indicates that the system can measure continuously for over one year without changing the cylinders for calibration gases. The developed oxygen measurement system is likely to be suitable for in situ atmospheric observation because of its high measurement precision and capability to use fewer high-pressure gas cylinders.

Fine and targeted tuning of a single quadrupole MS hyphenated with gas chromatography using Taguchi method

Fine-tuning of the mass spectrometer (MS) is necessary before the analysis of the test samples for better performance, fault-free operation, and lower limit of detection (LOD) value. It is usually done on the basis of the response of calibration gas perfluoro tributyl amine. The voltages of the lenses, multiplier, and prefilter are the significant factors influencing the response of the calibration gas, and getting their optimized/targeted value consumes plenty of time for the scientists. To overcome this issue, a Taguchi model using an L25 orthogonal array has been developed to tune the single quadrupole MS rapidly. The model fit was calculated for the specific m/z ions 69, 100, 131, 219, 264, 414, and 502 of calibration gas and found to range from 96.92 % to 99.03 %. The model-calculated values were compared with the actual values, and there was a 98 % correlation between them. Apart from that, the tuned MS was utilized for the determination of the LOD of pentafluorobenzoic acid methyl ester and found the reduced LOD of 5.4 ng/mL.

Verification Gas Mixtures are the Metrological Basis of Life Safety

The article pays attention to the influence of air pollution on the safety of human life. The issue of production and application of domestic standard samples of calibration gas mixtures as a metrological basis in the process of ensuring the safety of life is considered. General information is provided on standard samples of calibration gas mixtures – metrological purpose, types, methods of production, packaging. The article provides an analysis of the nomenclature of produced calibration gas mixtures mastered by the Karaganda branch of the Republican State Enterprise «Kazakhstan Institute of Standardization and Metrology». Special attention is paid to the component composition of the standard samples produced. The demand for these standard samples in the country has been investigated. The prospects for further expansion of production are given.

A case study for in-house method validation of gas chromatography technique using class-1 calibration gas mixtures for greenhouse gases monitoring

A case study for in-house method validation of gas chromatography technique using class-1 calibration gas mixtures for greenhouse gases monitoring

Quantification of trace fenuron in waste water samples by matrix matching calibration strategy and gas chromatography-mass spectrometry after simultaneous derivatization and preconcentration.

This study presents a highly sensitive and accurate analytical strategy for the determination of fenuron in wastewater samples using gas chromatography-mass spectrometry (GC-MS). Simultaneous derivatization and spray-based fine droplet formation-liquid phase microextraction (SFDF-LPME) method was developed and performed to achieve low detection limits. The parameters of the derivatization and SFDF-LPME method were optimized by univariate approach to improve sensitivity and selectivity. Under the optimum SFDF-LPME-GC-MS conditions, the limit of detection (LOD) and limit of quantitation (LOQ) were found to be 0.15 and 0.49 mg/kg, respectively. In addition, the linear range was calculated as 0.51-24.50 mg/kg. Recovery studies were carried out on wastewater samples to determine the accuracy of the developed method and its applicability to real sample matrix. Matrix matching calibration strategy was applied to eliminate/reduce any possible interference effects caused by the complexity of the wastewater matrix and to increase the accuracy of the analytical results. Percent recovery results varied between 85.9 and 120.9% with small percent relative standard deviation values. These results were satisfactory in terms of the accuracy and applicability of the proposed method for wastewater samples.

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.

Variable microfluidic dosing valve for gas chromatography

Miniaturization coupled with the introduction of microfluidic systems and devices into the chromatograph hardware is one of the main approaches to the creation of modern gas chromatographic equipment. For variable sample dosing in automatic mode, a microfluidic dosing valve based on microelectromechanical systems was developed. The manufactured device provides multi-point calibration with a single calibration gas mixture. Two methods for constructing a calibration dependence were implemented using the developed dosing device: a calibrated loop for 250 μl taken as a constant dosing loop and calibration solutions (gas mixtures of propane in helium (GSO 10463–2014) with concentrations of 0.0025, 0.025, 0.25, 0.5б and 1.25 % vol.) were used in the first method, whereas in the second one a variable dosing provided by the developed microfluidic dosing valve which consisted in the possibility of introducing a different amount of the calibration gas mixture of propane in helium (2.5 % vol.) into the chromatographic column due to changing the time of sample injection at a constant pressure was implemented. The experiment was carried out on a PIA gas microchromatograph with a MEMS column (a sectional plane of 1 × 1 mm and a 1-m channel) with a Carbopak B adsorbent. It is shown that the use of the developed dosing device as part of the PIA gas microchromatograph makes it possible to carry out a metrologically assured quantitative analysis.

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.

Investigation of the discharge coefficient in the laminar boundary layer regime of critical flow Venturi nozzles calibrated with different gases including hydrogen

This study represents the first step towards the introduction of critical flow Venturi nozzles into the traceability scheme for gaseous hydrogen and addresses the characterisation of the hydrogen discharge coefficient in the laminar boundary layer regime and the identification of a potential alternative gas for nozzle calibration. The experimental study presented was performed for two nozzles with a throat diameter of 0.175 mm and 0.436 mm. The tests were performed with six different gases, including hydrogen, covering a Reynolds number range from 1.5·103 to 6·104. The experimental results show that the discharge coefficient depends not only on the Reynolds number but also on the isentropic exponent of the gas. Based on the experimental data, theoretical models taking into account the isentropic exponent and the Prandtl number of the gas were evaluated. The study indicates possibilities to use inert gases instead of hydrogen in calibration processes.

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

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

On-Site Sensor Calibration Procedure for Quality Assurance of Barometric Process Separation (BaPS) Measurements

Barometric process separation (BaPS) is an automated laboratory system for the simultaneous measurement of microbial respiration and gross nitrification rates in soil samples. To ensure optimal functioning, the sensor system, consisting of a pressure sensor, an O2 sensor, a CO2 concentration sensor, and two temperature probes, must be accurately calibrated. For the regular on-site quality control of the sensors, we developed easy, inexpensive, and flexible calibration procedures. The pressure sensor was calibrated by means of a differential manometer. The O2 and CO2 sensors were simultaneously calibrated through their exposure to a sequence of O2 and CO2 concentrations obtained by sequentially exchanging O2/N2 and CO2/N2 calibration gases. Linear regression models were best suited for describing the recorded calibration data. The accuracy of O2 and CO2 calibration was mainly affected by the accuracy of the utilized gas mixtures. Because the applied measuring method is based on the O2 conductivity of ZrO2, the O2 sensor is particularly susceptible to aging and to consequent signal shifts. Sensor signals were characterized by high temporal stability over the years. Deviations in the calibration parameters affected the measured gross nitrification rate by up to 12.5% and affected the respiration rate by up to 5%. Overall, the proposed calibration procedures are valuable tools for ensuring the quality of BaPS measurements and for promptly identifying sensor malfunctions.

74 Evaluation of the Performance of a Robotic System for Spiking Thermal Desorption Sorbent Tubes with Defined Masses of Organic Compounds

Abstract Thermal desorption (TD) gas chromatography is a widely used analytical method for measuring airborne concentrations of (semi) volatile organic compounds ((S)VOCs) collected using sorbent tube samplers and is now widely used in the ambient, fence line, indoor and workplace air monitoring environments. Calibration and internal quality control check samples are prepared in end user laboratories by spiking individual TD sorbent tubes with microliter quantities of (S)VOCs in a carrier solvent such as methanol but this can be a laborious and error-prone step. Historically spiked sorbent certified reference materials were available from IRMM for confirmatory purposes but these stocks are now virtually exhausted. Hence new spiked tubes would be useful for quality control/assurance purposes. Previously HSE developed a system for the simultaneously spiking of 60 TD sorbent tubes with defined mases of VOCs from the gas-phase based upon requirements set out in ISO 6145 part 4[1]. With less volatile (S)VOCs however, spiking from the gas-phase presents challenges and hence an alternative spiking approach using liquid standards is proposed. The performance of a newly acquired automated robotic spiking system will be described. Reference [1] ISO 6145-4:2004. Gas Analysis-Preparation of calibration gas mixtures using dynamic volumetric methods-Part4: Continuous syringe injection method.