Combination Of Thermal Desorption Research Articles

Mechanism of hydrogen isotope exchange for tritium removal in plasma-facing materials: a multi-scale investigation

The safety of future fusion reactors is critically dependent on the tritium (T) retention in plasma-facing materials. Hydrogen isotope (HI) exchange offers a method to redistribute HIs within solid materials, presenting a feasible approach for removing T from bulk materials and trapped by strong trapping sites. Nonetheless, unraveling the intricate mechanism behind HI exchange remains an urgent yet formidable challenge. This study undertakes a comprehensive investigation into the mechanism of HI exchange in tungsten materials across multiple scales. First, we developed a multi-component hydrogen isotope transport and exchange model (HIDTX) based on classical rate theory. The model validation was further carried out, demonstrating good consistency with the well-controlled laboratory experiments. From the results of different comparative models in HIDTX, it is found that the reduction in deuterium retention due to HI exchange was primarily driven by three synergistic effects: competitive re-trapping, collision, and swapping effects. Through molecular dynamics (MD) and first-principles calculations, the microscopic mechanism of HI exchange was revealed to be that the presence of hydrogen atoms in the interstitial sites surrounding a vacancy in tungsten decreased the binding energy between the vacancy and hydrogen. Meanwhile, we discovered that the combination of thermal desorption and HI exchange can significantly lower the temperature required for the hydrogen removal and enhance the removal rate. Particularly, the hydrogen removal time can be shortened by approximately 95% with simultaneous HI exchange compared to that with only thermal desorption. This work provides a practical guideline for comprehending and subsequently designing for efficient T removal in future nuclear fusion materials.

Rapid desorption and analysis for illicit drugs and chemical profiling of fingerprints by SICRIT ion source.

Forensic analysis can encompass a wide variety of analytes from biological samples including DNA, blood, serum, and fingerprints to synthetic samples like drugs and explosives. In order to analyze this variety, there are various sample preparation techniques, which can be time-consuming and require multiple analytical instruments. With recent advancements in ambient ionization mass spectrometry (MS), plasma-based dielectric barrier discharge ionization (DBDI) sources have demonstrated to cover a wide range of these analytes. The flow-through design of this source also allows for easy connection to a thermal desorption type of sample introduction. We present an in-house built thermal desorption device where the sample is introduced via a glass slide, which gets heated and transferred to the DBDI-MS with nitrogen for identification and semi-quantification. Using a glass slide as an inexpensive sampling device, detection limits as low as 20 pg for fentanyl are demonstrated. Additionally, a very precise (>96% accuracy) identification of persons based on the chemical profile of their fingerprints is possible, establishing a direct analytical link of the drug trace to the individual in one measurement. We compared the DAG, TAG, sterol, and (semi-)volatile region of the averaged fingerprint spectra over multiple days, showing the best model accuracy for identification based on the DAG region. The combination of thermal desorption and DBDI-MS minimized sample preparation, leading to an ultrasensitive and rapid analysis of illicit drug traces and the identification of underlying personas based on fingerprints.

Enhanced mercury removal performance of Cu-Fe binary oxide sorbents modified by non-thermal plasma

In this work, magnetic Cu-Fe binary oxide (CF) sorbents synthesized by sol − gel method are modified by oxygen non-thermal plasma for efficient removal of elemental mercury (Hg0) from coal-fired flue gas. Sample characterization indicates that plasma treatment has very little impact on the physical properties, magnetization characteristics, and crystalline phases of CF sorbents. But the content of Fe3+, Cu2+, and lattice oxygen in CF sorbents are significantly improved after plasma treatment. Mercury adsorption experiments suggest that the modified sorbents show higher Hg0 removal efficiency in comparison with raw sorbents, and longer treatment time leads to higher Hg0 removal efficiency. The effect of plasma discharge power (32–96 VA), discharge atmosphere (N2, air, 50% N2 + 50% O2, and O2), and reaction temperature (50–350 °C) on mercury removal performance are also explored in a fixed-bed reactor. The presence of O2, NO, and HCl promote Hg0 removal. SO2 and H2O suppress Hg0 removal, but O2 addition can obviously weaken such inhibitory effects. Both experimental results and kinetic model indicate that chemisorption is the decisive factor for Hg0 removal over CF sorbents. Moreover, the mechanism of Hg0 removal over the modified CF sorbents is also investigated. The results indicate that Fe2O3 and CuO serving as active sites are greatly consumed in Hg0 removal process. The multiple regeneration cycles testify that the combination of thermal desorption and non-thermal plasma treatment can realize the efficient regeneration of CF sorbents.

Mercury's subsolar sodium exosphere: an ab initio calculation to interpret MASCS/UVVS observations from MESSENGER

Abstract. The optical spectroscopy measurements of sodium in Mercury's exosphere near the subsolar point by MESSENGER Mercury Atmospheric and Surface Composition Spectrometer Ultraviolet and Visible Spectrometer (MASCS/UVVS) have been interpreted before with a model employing two exospheric components of different temperatures. Here we use an updated version of the Monte Carlo (MC) exosphere model developed by Wurz and Lammer (2003) to calculate the Na content of the exosphere for the observation conditions ab initio. In addition, we compare our results to the ones according to Chamberlain theory. Studying several release mechanisms, we find that close to the surface, thermal desorption dominates driven by a surface temperature of 594 K, whereas at higher altitudes micro-meteorite impact vaporization prevails with a characteristic energy of 0.34 eV. From the surface up to 500 km the MC model results agree with the Chamberlain model, and both agree well with the observations. At higher altitudes, the MC model using micro-meteorite impact vaporization explains the observation well. We find that the combination of thermal desorption and micro-meteorite impact vaporization reproduces the observation of the selected day quantitatively over the entire observed altitude range, with the calculations performed based on the prevailing environment and orbit parameters. These findings help in improving our understanding of the physical conditions at Mercury's exosphere as well as in better interpreting mass-spectrometry data obtained to date and in future missions such as BepiColombo.

Determination of volatile organic compounds in ambient air by thermal desorption-gas chromatography-triple quadrupole tandem mass spectrometry

A method was established for the simultaneous determination of 23 volatile organic compounds (VOCs) in ambient air with combination of thermal desorption (TD) and gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS). The air samples were collected by active sampling method using Tenax-TA sorbent tubes, and desorbed by thermal desorption. The analytes were determined by GC-MS/MS in selected reaction monitoring (SRM) mode, and internal standard method was applied to quantify the VOCs. The results of all the 23 VOCs showed good linearities in low level (0. 01-1 ng) and high level (1-100 ng) with all the correlation coefficients (r2) more than 0. 99. The method quantification limits were between 0. 000 08-1 µg/m3. The method was validated by means of recovery experiments (n = 6) at three spiked levels of 2, 10 and 50 ng. The recoveries between 77% and 124% were generally obtained. The relative standard deviations (RSDs) in all cases were lower than 20%, except for chlorobenzene at the low spiked level. The developed method was applied to determine VOCs in ambient air collected at three sites in Shanghai. Several compounds, like benzene, toluene, ethylbenzene, m-xylenes, p-xylenes, styrene, 1, 2, 4-trimethylbenzene and hexachlorobutadiene were detected and confirmed in all the samples analyzed. The method is highly accurate, reliable and sensitive for monitoring the VOCs in ambient air.

Detection of acetone and isoprene in human breath using a combination of thermal desorption and selected ion flow tube mass spectrometry

The measurement of volatile chemicals in human exhalant (breath analysis) has recently emerged as a non-invasive technique with the potential for the early diagnosis of disease. A common method of volatile chemical collection is to capture gases onto a solid phase sorbent followed, at a later time, by thermal release and analysis. This technique, termed thermal desorption (TD), may be a useful means to collect and store breath volatiles in a clinical setting prior to analysis. TD is, however, normally used in conjunction with gas chromatography (TD–GC) which results in slow analysis times and the required use of chemical standards. The new technique of selected ion flow tube mass spectrometry (SIFT-MS) offers a more rapid analysis process without the need for standards. SIFT-MS is normally used to analyze gas concentration in real-time and it is unclear whether combined TD and SIFT-MS can be successfully employed for breath analysis. We found that there was an approximate 1 to 1 concordance between levels of isoprene or acetone in the breath of 12 healthy volunteers measured either using real-time SIFT-MS or offline using a combination of SIFT-MS and TD (TD–SIFT-MS). The use of higher volumes of human breath did impact TD–SIFT-MS measurements of isoprene (but not acetone) with an apparent ceiling effect being observed. Nevertheless our findings demonstrate the potential for breath analysis using a combination of TD and SIFT-MS, an approach which may find utility in a clinical setting which does not allow online analysis of breath.

The combined use of thermal desorption and selected ion flow tube mass spectrometry for the quantification of xylene and toluene in air

Thermal desorption (TD) is commonly employed for volatile chemical analysis, it being the method of choice for occupational health and safety monitoring. TD allows for offline capture of volatiles onto a solid sorbent followed by desorption and analysis at a later time. Although TD is routinely used in conjunction with gas chromatography (TD-GC), the assay throughput is low and requires the use of gas standards for quantification. Another technique increasingly employed for volatile chemical analysis, selected ion flow tube mass spectrometry (SIFT-MS), is capable of real-time absolute (i.e. without calibration standards) quantification of volatile chemicals present at single digit parts per billion or higher concentrations. SIFT-MS is, however, normally used for online direct analysis of gas samples rather than offline collection and analysis. The goal of this study was to determine whether a combination of TD and SIFT-MS could be used to quantify volatile compounds, specifically xylene and toluene, more rapidly than TD-GC and without the need for calibration standards. SIFT-MS was able to quantify xylene and toluene levels within 45 s of desorption. Due to the robustness of the SIFT-MS analysis in the presence of water vapour and other major components of air, the purging of tubes usually required to remove these constituents during the TD cycle was not required, therefore reducing the TD cycle time. Comparing the quantity of xylene and toluene applied to the TD tube with the absolute levels quantified by SIFT-MS subsequent to desorption suggested a recovery of over 95% of the applied compound. We conclude that the combination of TD and SIFT-MS allows more rapid and accurate quantification of xylene and toluene (compared with TD-GC) to be achieved without the need for calibration standards, features which may be advantageous in applications requiring rapid analysis and high throughput.

Chemical characterization of odors due to some industrial and urban facilities in Izmir, Turkey

The relationship between odor concentrations (olfactometry) and chemical concentrations (gas chromatography-mass spectrometry, GC-MS) was studied for the odorous air compositions of a rendering plant, a sanitary landfill and an industrial area with large petroleum and petrochemical industries. Samples taken from the university campus located in a non-industrial and non-urban area were also studied for several organic components for comparison. Ambient air samples were taken into special bags by using an odor sampling device designed for field sampling of odors. In the laboratory odorous chemicals in the samples were transferred into adsorbent tubes and analyzed using a combination of thermal desorption and GC-MS. Results point to different characteristics of the odorous gases and air in and around the urban and industrial sources. Among the 64 specific compounds studied, 49 volatile organic compounds (VOCs) were detected in rendering plant, 53 VOCs were detected in sanitary landfill and 44 VOCs were detected in petroleum and petrochemical industries. The compounds measured in the odorous gas composition are the alkanes, alkenes, carbonyls, arenes, chlorinated and other halogenated compounds and organic chlorides as well as the volatile fatty acids.

Oxygen chemisorption on sodium-form zeolites and its effect on the hydrogenating activity of catalysts

1. The treatment of NaX and NaY zeolites with an inert gas (helium or argon) at 520‡C immediately after their high-temperature treatment with air significantly increases the activity of the catalysts in benzene hydrogenation. 2. Oxygen chemisorption on NaX zeolite at 550‡C was observed by a combination of thermal desorption and mass spectrometry. 3. The obtained data suggest that in high-temperature treatment of zeolites with air, oxygen is chemisorbed on them, and, in the subsequent presence of hydrogen, this oxygen forms water which deactivates the catalyst.

Sampling and gas chromatographic analysis of volatile sulphur compounds and gases at sub-v.p.m. Levels in the presence of ozone

A method is presented for the sampling and analysis of sulphur gases (hydrogen sulphide and methanethiol) and volatile sulphur compounds (higher thiols and organic sulphides) in both ambient air samples and air containing ozone. The method has been developed for the quantitative analysis of hydrogen sulphide and for the semi-quantitative and qualitative analysis of other sulphur compounds. Field sampling and sample storage make use of simple cryogenic techniques and the analysis is carried out using a combination of thermal desorption and cryogenic re-trapping with sulphur-specific gas chromatography. Sample volumes of 100 ml and collection times of 1 min per sample are typically used for hydrogen sulphide in the range 0.1–1.0 volume parts per million (v.p.m.) with a limit of detection estimated to be better than 70 volume parts per billion (v.p.b.). The technique has been used in connection with odour control and measurement at a sewage treatment works, and in the assessment of odour control plant effectiveness.

Isolation, Concentration and Subsequent Analysis by Capillary Gas Chromatography of Trace Amounts of Organophosphorus Compounds from Aqueous Samples

Abstract Trace amounts (ppb or less) of phosphorus containing compounds present in aqueous samples are adsorbed on XAD-4 and subsequently eluted by means of ethyl acetate. The solvent and the eluted compounds are evaporated and swept over a Tenax-GC tube. This gas stripping method traps the phosphorus containing compounds together with only a small amount of the solvent whereas the water entrapped in the XAD step is removed simultaneously. The compounds are desorbed from the Tenax-GC tube and injected into the gas chromatograph using the combination of thermal desorption, cold trapping and flash heating. The subsequent analysis is carried out on a capillary column and the compounds are detected by means of a flame photometric detector. The various steps of the analytical procedure are discussed, including the recoveries of the different compounds studied and some instrumental aspects.