Calibration Of Mass Spectrometers Research Articles

Study on the provision of traceable flow rate of water vapor for calibrating a time-of-flight mass spectrometer

Forming a traceable flow rate is the key to mass spectrometer calibration, and the flow rate can be calculated through the conductance. The theoretical and experimental analysis of measuring the conductance of water vapor using the VΔp measurement method is presented, the measurement error of that method increases with the decrease of flow rate, which is due to the strong adsorption characteristic of water vapor. Based on the VΔp measurement method, a new method called the pΔt measurement method is proposed to give the relationship between the orifice conductance and the inlet pressure for water vapor, and the conductance can be calculated by measuring the time of pressure change, which can correct the adsorption influence of water vapor on the measurement of conductance. The relative standard uncertainty of the pΔt measurement method is 8%. The conductance of an orifice, whose diameter is about 22.2 µm, was measured by that method, and the measurement results agree well with the theoretical values. According to those two methods, an apparatus was developed to calibrate a miniature time-of-flight mass spectrometer (TOF-MS) for water vapor, and it can supply the flow rate of water vapor in the range from 3.67 × 10−9 to 2.19 × 10−5 Pa m3 s−1. Finally, there is a linear relationship between the signal and the flow rate for water vapor in the range from 1.39 × 10−8 to 1.29 × 10−5 Pa m3 s−1.

50 Years of uranium isotopic reference materials at JRC-Geel

The history of uranium isotopic reference materials from JRC-Geel during the last 50 years is reviewed by presenting certification methods and relevant applications. The certified isotope ratios are traceable to the SI via gravimetrical preparation, either directly through gravimetrical mixing of highly enriched materials, or indirectly using existing gravimetrically prepared reference materials for calibration of mass spectrometers used for certification measurements. Due to developments of mass spectrometers and analytical methods, certification measurements have improved regarding precision, uncertainties and accuracy. This has led to a comprehensive set of uranium isotopic reference materials available for nuclear safety, security and the scientific community.

Low-pressure gas flow properties of sintered stainless steel microporous media

The gas flows through the low permeable porous media are of great interest, especially in vacuum technology for filtering, separation processes, protection, and flow control. They can combine a high mass flow rate and a high level of rarefaction. The transient experimental technique, developed previously for the mass flow rate measurements through the microchannels [Rojas Cardenas et al., Phys. Fluids 23, 031702 (2011)], is generalized to obtain the permeability and conductance directly from the pressure variation measurements. The present experimental methodology, allowing for step by step data verification, leads to higher accuracy than the similar and commonly used method such as “pulse-decay” techniques [W. F. Brace and R. J. Martin, Int. J. Rock Mech. Min. Sci. 5, 415–426 (1968)]. The measured data are fitted according to the exponential function with the pressure relaxation time as a single fitting parameter. The permeability and conductance of the sintered stainless steel microporous medium are measured for different gases. By using the methodology proposed by Johansson et al. [Int. J. Heat Mass Transfer 142, 118412 (2019)], the characteristic pore size of the sample was determined to be equal to 1.5 micrometers. It was found that free molecular flow constant conductance is achieved at a pressure below 30 mbar for helium. This property makes this kind of porous media particularly suitable as a leak element by taking advantage of the constancy of conductance in the free molecular flow regime, for example, for calibration of ionization gauges or mass spectrometers [Yoshida et al., Measurement 45(10), 2452–2455 (2012)].

Rapid Mass Spectrometric Calibration and Standard Addition Using Hydrophobic/Hydrophilic Patterned Surfaces and Discontinuous Dewetting.

The rapid calibration chip (RCC) is a device that uses the fast and reproducible wetting behavior of hydrophilic/hydrophobic patterned surfaces to confine a series of differently sized droplets on a substrate to obtain a calibration curve. Multiple series of droplets can be formed within seconds by dipping an RCC into a calibration solution. No pipetting, sequential droplet deposition, or advanced equipment is required. The performance and reproducibility of RCCs were evaluated with an electrospray ionization triple-quadrupole mass spectrometer equipped with a liquid microjunction-surface sampling probe (LMJ-SSP) that allows for fast sampling of surfaces. Using circular hydrophilic areas with diameters ranging from 0.25 to 2.00 mm, liquid volumes of 4.6-70.6 nL could be deposited. Furthermore, the use of a second hydrophobic/hydrophilic patterned transfer chip can be used to add internal standard solutions to each calibration spot of the RCC, allowing to transfer a liquid volume of 22.5 nL.

Characterization of a Spatially resolved multi-element laser ablation ion source

A laser ablation ion source (LAS) is a powerful tool by which diverse species of ions can be produced for mass spectrometer calibration or surface study applications. It is necessary to frequently shift the laser position on the target to selectively ablate materials in a controlled manner, and to mitigate degradation of the target surface caused by ablation. An alternative to mounting the target onto a rotation wheel or x − y translation stage, is to shift the laser spot position with a final reflection from a motorized kinematic mirror mount. Such a system has been developed, assembled and characterized with a two axis motorized mirror and various metal targets. In the system presented here, ions are ablated from the target surface and guided by a 90° quadrupole bender to a Faraday cup where the ion current is measured. Spatially resolved scans of the target are produced by actuating the mirror motors, thus moving the laser spot across the target, and performing synchronous measurements of the ion current to construct 2D images of a target surface which can be up to 50 mm in diameter. The spatial resolution of the system has been measured by scanning the interfaces between metals such as steel and niobium, where it was demonstrated that the LAS can selectively ablate an area of diameter ≈50 μm. This work informs the development of subsequent LAS systems, that are intended to serve as multi-element ion sources for commercial and custom-built time-of-flight mass spectrometers, or to selectively study surface specific regions of samples.

Quantitative gas composition analysis method for a wide pressure range up to atmospheric pressure-CO2 plasma case study.

A mass spectrometer with a custom sampling system comprising one fixed and one variable orifice is presented. The custom sampling system allows the determination of the gas composition in the pressure range from 5 mbar to 1000 mbar, with low gas-demixing (<1.5%). A case study of mass spectrometer optimization and calibration for the measurement of relative concentration of CO2, CO, O2, and N2 gases is presented, together with an example of the CO2 conversion at a microwave plasma torch. The absolute error of the measured conversion of CO2 in CO is found to be less than 1.6% in the complete pressure range. The conversion determination routine presented here allows us to determine relative molar flows of CO2, CO, O2, and N2 and to distinguish between CO and N2 gases, which is important for the determination of the CO2 conversion in the case of air impurities or in the case of CO2/N2 mixtures.

The formation of NeH+ in static vacuum mass spectrometers and re-determination of 21Ne/20Ne of air

Abstract Air-derived neon is used for routine calibration of magnetic sector mass spectrometers, principally for determining sensitivity and mass discrimination for Ne isotope determinations. The commonly accepted 21Ne/20Ne ratio of air (0.002959 ± 0.000022; Eberhardt et al. (1965) does not take account of the contribution of 20NeH+ at m/z = 21. Honda et al. (2015) and Wielandt and Storey (2019) have recently re-determined the 21Ne/20Neair by resolving 20NeH+ from 21Ne+. The 21Ne/20Neair values of the two studies differ by 1.8%, beyond the uncertainty of the measurements (±

On reference method development for traceability of measurements of the mercury content in gaseous media

To certify gas mixtures in the range of low (10 -3 -10 -8 g/m 3 ) mercury concentrations, we have proposed and tested a traceable method for measuring the mass concentration of mercury in gaseous media by inductively coupled plasma mass spectrometry (ICP/MS). The proposed method is based on a scheme that provides for the mass spectrometer calibration for saturated vapors (physical constant) of pure metallic mercury, dosed directly into the carrier gas stream - argon. The undoubted advantage of this method is its applicability to various gases and gas mixtures, which allows you to simulate any matrix medium that affects the measurement results of mercury content when analyzed by other methods. On this basis, «Methods of measuring the mass concentration of mercury in binary gas mixtures by ICP/MS» were developed and certified. The measurement range of mercury mass concentration is from 0,03 to 1000 pg/m 3 , the relative expanded uncertainty of measurements U- 4 %.

A Hardware and Software Facility for Calibration and Adjustment of Ion Mass Spectrometers for Space Missions

The characteristics of a hardware–software facility for laboratory adjustments and calibrations of plasma energy–mass spectrometers, which are created within the framework of Russian and international space missions, are presented. The principle of operation of the ARIES-L instrument is described and the results of functional tests of instruments that were obtained using the hardware–software facility are presented.

History of very thick film and bulk sample group IIIB, IVB, VB, and rare earth materials for various vacuum applications

Thick occluder film and bulk hydride materials are extremely hard to produce without flaking or cracking. This paper discusses methods of how to prepare thick films and bulk samples (i.e., rods and wires) that have reduced stress for many applications. These include accelerator research for cancer therapy, intense neutron sources, particle-beam fusion diagnostic beam focusing studies, and mass spectrometer calibration. Thick films of ∼(≥3000 to 150 000 nm thickness of various hydrides are sensitive to oxidation and are easily contaminated by improper handling. They must be specially prepared to reduce internal stresses due to temperature variations during processing, stresses due to hydriding, and substrate configuration (i.e., curved surfaces). Discussed are techniques developed at the General Electric Neutron Devices Department, in Largo, FL, in the mid-1970s to the late 1990s to produce flaking and crack free samples of thick films and bulk samples. Items studied include Er, Sc, and Ti thick film hydrides on a Cr underlay, on various substrates, Er and Sc bulk rod samples for the first basic material heat capacity and thermal diffusivity studies as a function of hydride loading, Nb and V wires in bundles of ∼30 wires, for the first tritide neutron vibration spectra studies, and Ti wires for mass spectrometer calibration studies. Film samples were prepared by standard E-beam evaporation techniques and then non-air-exposure loaded. Bulk samples were loaded with a Sievert's precise gas quantity loading system. To produce reduced intrinsic stress (strain) in samples of Er, Sc, and Ti thick films, and bulk samples of Er, Sc, Nb, V, and Ti, special processing employing slow bakeout heating and cool down rates, slow film deposition rates, slow leak in pressure hydriding rates, followed by slow cooling rates to room temperature were used. Using the process described, very successful results were obtained.

A low energy ion beam facility for mass spectrometer calibration: First results.

The exploration of habitable environments around the gas giants in the Solar System is of major interest in upcoming planetary missions. Exactly this theme is addressed by the Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA), which will characterise Ganymede, Europa, and Callisto as planetary objects and potential habitats. The NIM, Neutral gas and Ion Mass spectrometer, is part of the PEP experiment and will be used to measure the chemical composition of the exospheres of the icy Jovian moons. We designed and developed a calibration facility (SATANS, Supersonic cATion and ANion Source), especially for use with the NIM instrument. In a first step, we established a low energy ion beam for positive ions in the range of 0.01-30 eV. Then we conducted beam velocity calibrations with a velocity uncertainty <5%, which provided exact settings and formulas for the cation beam velocity of different gas mixtures in the range of 1-15 km/s. In addition, first results are obtained by using the NIM prototype for direct ion beam measurements under realistic JUICE mission conditions, i.e., for velocities from 1 up to 7 km/s and even more.

UV photoprocessing of CO2ice: a complete quantification of photochemistry and photon-induced desorption processes

Context. Ice mantles that formed on top of dust grains are photoprocessed by the secondary ultraviolet (UV) field in cold and dense molecular clouds. UV photons induce photochemistry and desorption of ice molecules. Experimental simulations dedicated to ice analogs under astrophysically relevant conditions are needed to understand these processes.Aims. We present UV-irradiation experiments of a pure CO2 ice analog. Calibration of the quadrupole mass spectrometer allowed us to quantify the photodesorption of molecules to the gas phase. This information was added to the data provided by the Fourier transform infrared spectrometer on the solid phase to obtain a complete quantitative study of the UV photoprocessing of an ice analog.Methods. Experimental simulations were performed in an ultra-high vacuum chamber. Ice samples were deposited onto an infrared transparent window at 8K and were subsequently irradiated with a microwave-discharged hydrogen flow lamp. After irradiation, ice samples were warmed up until complete sublimation was attained.Results. Photolysis of CO2 molecules initiates a network of photon-induced chemical reactions leading to the formation of CO, CO3 , O2 , and O3 . During irradiation, photon-induced desorption of CO and, to a lesser extent, O2 and CO2 took place through a process called indirect desorption induced by electronic transitions, with maximum photodesorption yields (Y pd ) of ~1.2 × 10-2 molecules incident photon-1 , ~9.3 × 10-4 molecules incident photon-1 , and ~1.1 × 10-4 molecules incident photon-1 , respectively.Conclusions. Calibration of mass spectrometers allows a direct quantification of photodesorption yields instead of the indirect values that were obtained from infrared spectra in most previous works. Supplementary information provided by infrared spectroscopy leads to a complete quantification, and therefore a better understanding, of the processes taking place in UV-irradiated ice mantles.

Chemical ionization mass spectrometry using carbon nanotube field emission electron sources.

A novel chemical ionization (CI) source has been developed based on a carbon nanotube (CNT) field emission electron source. The CNT-based electron source was evaluated and compared with a standard filament thermionic electron source in a commercial explosives trace detection desktop mass spectrometer. This work demonstrates the first reported use of a CNT-based ion source capable of collecting CI mass spectra. Both positive and negative modes were investigated. Spectra were collected for a standard mass spectrometer calibration compound, perfluorotributylamine (PFTBA), as well as trace explosives including trinitrotoluene (TNT), Research Department explosive (RDX), and pentaerythritol tetranitrate (PETN). The electrical characteristics, lifetime at operating pressure, and power requirements of the CNT-based electron source are reported. The CNT field emission electron sources demonstrated an average lifetime of 320 h when operated in constant emission mode under elevated CI pressures. The ability of the CNT field emission source to cycle on and off can provide enhanced lifetime and reduced power consumption without sacrificing performance and detection capabilities. Graphical Abstract ᅟ.

Outgassing rate measurements with the difference method in the framework of EMRP IND12

A new outgassing rate facility applying the difference method was established at KIT. This system was validated within the framework of Joint Research Project IND 12 of the European metrology Research programme by several outgassing reference probes. These served as transfer standards for comparison with three other outgassing rate systems available in the project. Two of the probes were newly developed reference devices and exhibit a known, constant outgassing rate of water. Further two probes were also newly developed outgassing reference devices which emit mixtures of gases. Additionally another probe was an elastomer which was loaded with a known gas mixture. The last probe was a commercially available plastic material whose outgassing shows a large spectrum of gases. The other outgassing rate facilities applied the in-situ calibration of quadrupole mass spectrometers by a primary method, the continuous expansion method (Physikalisch-Technische Bundesanstalt) and the known gas quantity method (Institute of Metals and Technology) or the throughput method (VACOM company).The comparison of the results shows a satisfactory agreement between the measurements.

Molybdenum isotope enrichment by anion-exchange chromatography

Stable enriched isotopes with an abundance as close to 100% as possible are most desirable parent materials for preparing synthetic isotope mixtures for calibration of mass spectrometers. In this study, we have examined the extent of Mo isotope fractionation during anion-exchange chromatography and assessed the potential of this separation technique for further isotope enrichment of commercially available isotopically enriched molybdenum. The 60 cm wide molybdenum adsorption band was eluted from a 1.8 m long (3 times 60 cm) chromatographic column, filled with strongly basic anion-exchange resin. It was observed that heavier Mo isotopes were preferentially eluted from the resin, resulting in an enrichment of heavier Mo isotopes at the front of the adsorption band and a corresponding depletion at the rear. An equilibrium isotope effect between dissolved and resin-bound chemical forms of molybdenum appears to be the cause of the Mo isotope fractionation observed. The height equivalent to a theoretical plate (HETP) was calculated to be 0.25 mm, while the separation factor (α = Rresin/Rsolution) was found to be 0.99998 per atomic mass unit. These results show that molybdenum can, in principle, be further enriched isotopically by anion-exchange chromatography in a laboratory environment. However, achieving the highest degree of enrichment was confirmed to be very laborious. It has been estimated that in order to reach an increase in the abundance of 98Mo isotope from an original value of 98.2% to 99.9%, the molybdenum adsorption band would need to migrate over a distance of at least 400 m through the anion-exchange resin. Another interesting observation made in this study was that no mass-independent isotope fractionation was observed for molybdenum as a result of chemical exchange reactions on the anion-exchange resin.

The work of ISO TC 112 towards standardization for specification and calibration of quadrupole mass spectrometers

Absolute quantitative measurements of partial pressures with quadrupole mass spectrometers in industry have become increasingly important in the past decade. On the other hand, there is no broadly accepted method to calibrate quadrupole mass spectrometers and partial pressure measurements are not traceable to the SI. For this reason the ISO Technical Committee 112 for vacuum technology is taking steps to improve this situation by standardization.

Spectrophotometric method for precision determination of elements of the nuclear fuel cycle

Published data on precision spectorphotometric determination of U, Th, Pu, and other elements of the nuclear fuel cycle in solutions on a two-channel analyzer with the relative random uncertainty S r = 0.1–0.2% are summarized. The method was used for certification and fabrication of Pu and U total weight fraction standards for mass spectrometer calibration. New data on precision determination of U, Ru, Er, Gd, Sm, Re, and Tc on serial Shimadzu UV devices in the photometric mode with the relative random uncertainty S r = 0.02–0.04% are presented. The relative total uncertainty that can be attained with the spectrophotometric method is as low as 0.03–0.05%, which makes this method competitive with other precision methods used.

Newly developed standard conductance element for in situ calibration of high vacuum gauges

A new leak element, which is named as “standard conductance element (SCE)”, has been developed for in situ calibration of ionization gauges (IGs) and quadrupole mass spectrometers (QMSs). The SCE is made of a stainless-steel sintered filter with the pore size of less than 1μm. Since the gas flow through the SCE satisfies the molecular flow condition even at the pressure up to 104Pa, some useful characteristics of molecular flow are available. The SCE is supplied to users with a calibration certificate described its molecular conductance. Users can introduce optional test gases with the known flow rate to their vacuum chamber through the SCE in their laboratories. The overview of the SCE, the calibration method and recommended practices are introduced.

A metrological approach to measuring40Ar* concentrations in K-Ar and40Ar/39Ar mineral standards

In geochronology, isotopic ages are determined from the ratio of parent and daughter nuclide concentrations in minerals. For dating of geological material using the K-Ar system, the simultaneous determination of 40Ar and 40K concentrations on the same aliquot is not possible. Therefore, a widely used variant, the 40Ar/39Ar technique, involves the production of 39Ar from 39K by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux, referred to as “mineral standards.” Many mineral standards still in use rely on decades-old determinations of 40Ar concentrations; resulting uncertainties, both systematic and analytical, impede the determination of higher accuracy ages using the K-Ar decay system. We discuss the theoretical approach and technical design of a gas delivery system which emits metrologically traceable amounts of 40Ar and will allow for the sensitivity calibration of noble gas mass spectrometers. The design of this system is based on a rigorous assessment of the uncertainty budget and detailed tests of a prototype system. A number of obstacles and proposed resolutions are discussed along with the selection of components and their integration into a pipette system.

Mass spectrometer calibration over wide concentration ranges in multicomponent gas mixtures

A quadrupole mass spectrometer (QMS) is used to measure the mixture composition of gas samples gathered in a novel burner configuration used to generate unstretched diffusion flames. The large variations of species concentration in the mixtures found in the burning chamber lead to accuracy problems due to the nonlinearities inherent to the instrument mode of operation. To obtain precise and real-time measurements, the sensitivity of the instrument is mapped to account for important changes in the sample composition. The implemented calibration procedure accounts for the concentration of the various species of interest in the burner (H2, He, H2O, CH4, O2, Ar, CO2) in mixtures containing up to five constituents, using up to one hundred reference mixtures. When necessary, calibration adjustments are performed using a small set of measurements to account for the effect of the drift of instrument sensitivity resulting from instrument wear or fouling. This procedure allows us to keep the relative error on the concentration of every species of interest below 5% for most of the mixtures while a classical calibration based on a limited number of reference mixtures often resulted in relative errors in excess of 50%.