Quantitative secondary ion mass spectrometry imaging of self-assembled monolayer films for electron beam dose mapping in the environmental scanning electron microscope

Fluorinated alkanethiol self-assembled monolayers (SAM) films immobilized on gold substrates have been used as electron-sensitive resists to map quantitatively the spatial distribution of the primary electronbeam scattering in an environmental scanning electron microscope (ESEM). In this procedure, a series of electron dose standards are prepared by exposing a SAM film to electron bombardment in well-defined regions at different levels of electron dose. Microbeam secondary ion mass spectrometry (SIMS) using Cs⁺ bombardment is then used to image the F^- secondary ion signal from these areas. From the reduction in F^- intensity as a function of increasing electron dose, a calibration curve is generated that allows conversion of secondary ion signal to electron dose on a pixel-by-pixel basis. Using this calibration, electron dose images can be prepared that quantitatively map the electron scattering distribution in the ESEM with micrometer spatial resolution. The SIMS imaging technique may also be used to explore other aspects of electron-surface interactions in the ESEM.     

Calibration of the LHCb electromagnetic calorimeter using the technique of neutral pion invariant mass reconstruction

Calibration of the electromagnetic calorimeter for the LHCb experiment is aimed at measuring the electron and photon energies with an accuracy of 2% or better. A number of calibration techniques are sequentially used for this purpose. One of these techniques is based on reconstruction of the π⁰ meson invariant mass in a two-photon decay. Using this procedure, it is possible to calibrate the electromagnetic calorimeter in the transverse energy range of 300–1500 MeV. An important advantage of this technique is its independence of the states of the other LHCb spectrometer systems. Statistics sufficient for attaining the declared purpose can be rapidly acquired owing to the large cross section of neutral pion production in deep inelastic events. The algorithm has been implemented as a part of the LHCb software. The calibration procedure using neutral pions takes no more than 2 weeks and helps achieve the required accuracy.     

Low-vacuum cylindrical ion trap mass spectrometry

Low-vacuum mass spectrometry is desirable because it reduces the size, weight, cost, and power of the instrument by reducing the workload of the pumping system. To investigate low-vacuum mass spectrometry methods, a cylindrical ion trap (CIT) instrument was built. The platform used an electron impact source as the ionization source, a custom CIT as the mass analyzer, and an electron multiplier as the ion detector. The dimensions of the CIT were r₀?=?10?mm and z₀?=?8.98?mm. Aiming at low-vacuum conditions, its working parameters were optimized. By increasing the frequency of the radio frequency (RF) voltage, optimizing the electron impact source, using a higher voltage on the electron multiplier, and improving the current preamplifier, the mass spectrometry of methyl salicylate was successively performed at helium buffer gas pressures up to 2?Pa, which was dozens of times higher than the upper pressure limit of ion trap mass spectrometers. More importantly, this pressure can be obtained using a single pump, avoiding the use of a bulky turbo pump. In addition, we measured and analyzed the mass deviation of methyl salicylate with the changes in the background gas pressure and RF voltage frequency. The results experimentally verified the theory that the stability regions expand with increasing pressure for the first time. The methods we explored could be used to develop next generation hand-portable instruments and bring new applications to mass spectrometry.     

Elemental and molecular imaging of human hair using secondary ion mass spectrometry.

Secondary ion mass spectrometry (SIMS) is used to image the spatial distribution of elemental and molecular species on the surface and in cross sections of doped human hair using a magnetic sector SIMS instrument operated as an ion microprobe. Analysis of electrically insulating, non-planar hair samples requires one of two different methods of charge compensation to be used depending on the polarity of the sputtered secondary ions. For detection of positive secondary ions, the hair is imaged using a approximately 0.5 micron diameter, 19.5 keV impact energy, O- microbeam with no auxiliary electron bombardment. For detection of negative secondary ions, a approximately 0.2 micron diameter, 14.5 keV impact energy Cs+ microbeam is used in conjunction with normal incidence, low-energy electron bombardment. Both of these methods allow submicrometer spatial resolution elemental and molecular secondary ion images to be obtained from hair samples without metallic coating of the sample surface prior to analysis. Several examples are presented that reflect potential application areas for these analytical methods.     

质量比较仪校准结果的不确定度评定及CMC表示

质量比较仪是砝码量值传递系统最重要的配套设备。是基于ABA或ABBA循环方式测量质量差值,以全量程或电子秤量范围加配衡的秤量方式的高分辨率电子衡量设备。本文根据质量比较仪的工作原理和计量特征,分析质量比较仪校准结果不确定度的来源、评定方法和最佳校准能力的表示,为开展质量比较仪校准提供技术帮助。     

Quantitative STEM mass measurement of biological macromolecules in a 300 kV TEM

For almost four decades, the scanning transmission electron microscope (STEM) has made significant contributions to structural biology by providing accurate determinations of the molecular masses of large protein assemblies that have arbitrary shapes and sizes. Nevertheless, STEM mass mapping has been implemented in very few laboratories, most of which have employed cold field‐emission gun (FEG) electron sources operating at acceleration voltages of 100 kV and lower. Here we show that a 300 kV commercial transmission electron microscope (TEM) equipped with a thermally assisted Shottky FEG can also provide accurate STEM mass measurements. Using the recently published database of elastic‐scattering cross sections from the National Institute of Standards and Technology, we show that the measured absolute mass values for tobacco mosaic virus and limpet hemocyanin didecamers agree with the known values to within better than 10%. Applying the established approach, whereby tobacco mosaic virus is added to a specimen as a calibration standard, we find that the measured molecular weight of the hemocyanin assemblies agrees with the known value to within 3%. This accuracy is achievable although only a very small fraction (∼0.002) of the incident probe current of 300 kV electrons is scattered onto the annular dark‐field STEM detector. FEG TEMs operating at intermediate voltages (200–400 kV) are becoming common tools for determining the structure of frozen hydrated protein assemblies. The ability to perform mass determination with the same instrument can provide important complementary information about the numbers of subunits comprising the protein assemblies whose structure is being studied.     

Coriolis mass flow measurement at cryogenic temperatures

With the growing interest in liquefied natural gas (LNG) in the energy market, Coriolis mass flowmeters have been applied to many applications in the distribution of LNG. Since Coriolis flowmeters are normally calibrated at around room temperatures, measurements for LNG at cryogenic temperatures present a challenging condition. Firstly, a theoretical analysis for Coriolis mass flow sensors is provided considering the major changes of material properties (Young’s modulus and thermal expansion) at cryogenic temperatures. Then, a practical approach which can be used to correct the flow calibration factor obtained at a reference condition is presented. Finally, flow test results obtained from NIST’s cryogenic calibration facility are provided. Based on the results, it can be concluded that if a Coriolis flowmeter is calibrated at a reference condition and the flow calibration factor is corrected considering the non-linearity of Young’s modulus and thermal expansion change with temperature, it can still provide very accurate mass flow measurement even at cryogenic temperatures.     

Review of certain key issues in indirect measurements of the mass flow rate of solids in pneumatic conveying pipelines

On-line mass flow measurement of particulate solids in pneumatic conveying pipeline is a technically challenging area, where mass flow measurement presents a range of problems. These problems are not normally relevant to a single phase flow, but are always involved in gas–solids two-phase flows, like inhomogeneous distribution of solids over the pipe cross section, irregular velocity profiles, variations in particle size, moisture content, and deposition of fine particles on the inner wall of the pipeline. These variables may affect the response of a solids flow meter in ill-defined ways. All of these make the design and the calibration of solids’ mass flowmeter more difficult. Based on a review of non-invasive mass flow measurements of particulate solids, this paper summarizes and highlights several key issues, which often rely on structures of sensors or measurement methods, in indirect mass flow metering of pneumatically conveyed solids. They are: (i) spatial filtering effect; (ii) averaging effect; (iii) measurement resolution and sensitivity of array structures in tomography sensors.     

Linear quadrupoles in mass spectrometry

The use of linear quadrupoles in mass spectrometry as mass filters and ion guides is reviewed. Following a tutorial review of the principles of mass filter operation, methods of mass analysis are reviewed. Discussed are extensions of quadrupole mass filters to higher masses, scanning with frequency sweeps of the quadrupole waveform, operation in higher stability regions, and operation with rectangular or other periodic waveforms. Two relatively new methods of mass analysis the use of “islands of stability” and “mass selective axial ejection” are then reviewed. The optimal electrode geometry for a quadrupole mass filter constructed with round rods is discussed. The use of collisional cooling in quadrupole ion guides is discussed along with ion guides that have axial fields. Finally, mass analysis with quadrupoles that have large distortions to the geometry and fields is discussed. An Appendix gives a brief tutorial review of definitions of electrical potentials and fields, as well as the units used in this article. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:937–960, 2009     

Environmental analysis by inductively coupled plasma mass spectrometry

This article reviews the numerous ways in which inductively coupled plasma mass spectrometry has been used for the analysis of environmental samples since it was commercially introduced in 1983. Its multielemental isotopic capability, high sensitivity and wide linear dynamic range makes it ideally suited for environmental analysis. Provided that some care is taken during sample preparation and that appropriate calibration strategies are used to circumvent non‐spectroscopic interferences, the technique is readily applicable to the analysis of a wide variety of environmental samples (natural waters, soils, rocks, sediments, vegetation, etc.), using quadrupole, time‐of‐flight or double‐focusing sector‐field mass spectrometers. In cases where spectroscopic interferences arising from the sample matrix cannot be resolved, then separation methods can be implemented either on‐ or off‐line, which can simultaneously allow analyte preconcentration, thus further decreasing the already low detection limits that are achievable. In most cases, the blank, prepared by following the same steps as for the sample but without the sample, limits the ultimate detection limits that can be reached. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 29:560–592, 2010     

大质量比较仪校准结果计算及不确定度评定

大质量比较仪在大砝码量值传递与溯源中发挥着越来越重要的作用,本文依据JJF1326-2011《质量比较仪校准规范》和JJF1059．1-2012《测量不确定度评定与表示》,详细描述了大质量比较仪校准结果的计算及不确定度评定。     

同位素磁质谱仪的质量校正原理分析

同位素磁质谱仪的质量校正是准确质量数与准确磁场值之间的关系校正。质量校正后,以质量数操作取代磁场值操作,使质量控制更加精确,质谱综合控制能力进一步增强。校正曲线具有抛物线的数学特征,曲线不过零点,但起点靠近零点。质量校正是磁质谱方程的有条件运用。在实际工作中,这些条件最容易被误用,如高压值和参考通道。了解质量校正过程,有助于理解磁场不同工作模式特点、峰对中、宽窄杯混用、多接收杯位置关系、气体跳转测量、虚拟质量概念等。     

基于激光技术的振动定位器质量调态的研究

精密加工制作的振动定位器,是现代武器系统中定位、定向的关键器件,其质量调态是球型振动件加工的重要步骤。对基于激光技术的振动定位器质量调态进行了研究,系统地介绍了激光束调态的原理,振动件加工缺陷层的分布、形式和理论构成,去除缺陷的计算以及激光束工作时间的确定等问题。对应用激光束进行质量调态前后的缺陷情况的对比分析得出,机械加工后的球型振动件的振动分裂频差在0.5 Hz以上,而应用激光束进行质量调态的分裂频差为0.004 Hz,表明该方法是有效的。     

The isotopic distribution conundrum

Although access to high-resolution mass spectrometry (MS), especially in the field of biomolecular MS, is becoming readily available due to recent advances in MS technology, the accompanied information on isotopic distribution in high-resolution spectra is not used at its full potential, mainly because of lack of knowledge and/or awareness. In this review, we give an insight into the practical problems related to calculating the isotopic distribution for large biomolecules, and present an overview of methods for the calculation of the isotopic distribution. We discuss the key events that triggered the development of various algorithms and explain the rationale of how and why the various isotopic-distribution calculations were performed. The review is focused around the developmental stages as briefly outlined below, starting with the first observation of an isotopic distribution. The observations of Beynon in the field of organic MS that chlorine appeared in a mass spectrum as two variants with odds 3:1 lie at the basis of the first wave of algorithms for the calculation of the isotopic distribution, based on the atomic composition of a molecule. From here on, we explain why more complex biomolecules such as peptides exhibit a highly complex isotope pattern when assayed by MS, and we discuss how combinatorial difficulties complicate the calculation of the isotopic distribution on computers. For this purpose, we highlight three methods, which were introduced in the 1980s. These are the stepwise procedure introduced by Kubinyi, the polynomial expansion from Brownawell and Fillippo, and the multinomial expansion from Yergey. The next development was instigated by Rockwood, who suggested to decompose the isotopic distribution in terms of their nucleon count instead of the exact mass. In this respect, we could claim that the term "aggregated" isotopic distribution is more appropriate. Due to the simplification of the isotopic distribution to its aggregated counterpart, Rockwood was able to use the convolution for the calculation of the "aggregated" isotopic distribution. Convolution methods are computationally efficient and economic in their memory usage. We spend a section on the work introduced by Rockwood during the 1990s. Due to recent breakthroughs in mass spectrometric technology and the widespread high-resolution instruments (e.g., FTICR-MS, FTOrbitrap-MS, and TOF-MS) that provide high-resolution, isotope-resolved, accurate mass data, there is an emerging need for algorithms that can calculate isotopic distributions for large biomolecules. The number of recent publications on this topic does witness this trend. The new methods are mostly based on complex mathematical developments such as, for example, cellular automata (Meija and Caruso [2004]. J Am Soc Mass Spectrom, 15(5):654-658), dynamic programming (Snider [2007]. J Am Soc Mass Spectrom, 18:1511-1515), and hierarchical models (Li et al. [2008] J Am Soc Mass Spectrom, 19:1867-1874). We also comment on the ideas to use Punnet squares and Pascal's triangle to introduce the concept of the isotopic distribution for educational and didactic purposes.     

Estimation of mass thickness response of embedded aggregated silica nanospheres from high angle annular dark‐field scanning transmission electron micrographs

In this study, we investigate the functional behaviour of the intensity in high‐angle annular dark field scanning transmission electron micrograph images. The model material is a silica particle (20 nm) gel at 5 wt%. By assuming that the intensity response is monotonically increasing with increasing mass thickness of silica, an estimate of the functional form is calculated using a maximum likelihood approach. We conclude that a linear functional form of the intensity provides a fair estimate but that a power function is significantly better for estimating the amount of silica in the z‐direction. The work adds to the development of quantifying material properties from electron micrographs, especially in the field of tomography methods and three‐dimensional quantitative structural characterization from a scanning transmission electron micrograph. It also provides means for direct three‐dimensional quantitative structural characterization from a scanning transmission electron micrograph.     

A Coriolis mass flowmeter based on a new type of elastic suspension

After a survey of the existing Coriolis mass flowmeters, all based upon the elastic deformation of the resonant sensor, this paper describes a new type of Coriolis mass flowmeter realised, in a prototypal way, in the DIME laboratories. The flowmeter prototype is composed of two attached elements: a stiff tube and an original system of independent elastic suspension which lets the whole sensor vibrate. In such a way, the new type of elastic suspension permits measurement independent from the elastic properties of the tube, not subject to deformation, realising a new mass flow sensor. The DIME prototype, which is described in the present paper, was studied and realised with the main aim of checking the mechanical behaviour of the new type of uncoupled elastic suspension.

Being the prototype and not a production-engineered version, for which it is possible to provide the metrological performances, the DIME flowmeter was tested on the DIME calibration facility, and the experimental results, which prove the linear behaviour of the prototype, are reviewed.     

Calibration procedures and uncertainty analysis for a thermal mass gas flowmeter of a new generation

This paper deals with the differences between traditional and new technology gas meters, and focuses specifically on the calibration procedure and uncertainty evaluation of CTTMFs (Capillary Type Thermal Mass Flow Meter). In particular, measurements performed on a sample set of commercial CTTMFs for natural gas in domestic/residential (G4) applications allowed to evaluate the modifications to calibration procedures required by the new generation, digital, gas flow meters. Indeed, traditionally natural gas is metered by means of volumetric measurement techniques, while the modern, static gas flow meters (thermal and ultrasonic ones) are based on electronic flow sensors. This implies that the gas volume through the meter is measured by sampling the flow rate at selected time points and integrating the flow rate in time. The measurement time becomes therefore an important parameter, thus requiring a thorough rethinking of the calibration procedure. In order to analyse the effects of the various parameters, a series of ad-hoc calibrations were performed. Specifically, one set of calibrations was performed with constant totalized volume, while the other required a constant measurement time. In order to highlight the novelties that will have to be implemented in ordinary calibration procedures to get the best of the new technologies, the two procedures as performed on a sample set CTTMFs will be compared; the theoretical (generic) evaluation of the associated uncertainty will also be presented. Measurements were carried out at the test facility of INRIM, the Italian National Metrology Institute.     

Recent trends of capillary electrophoresis‐mass spectrometry in proteomics research

Progress in proteomics research has led to a demand for powerful analytical tools with high separation efficiency and sensitivity for confident identification and quantification of proteins, posttranslational modifications, and protein complexes expressed in cells and tissues. This demand has significantly increased interest in capillary electrophoresis‐mass spectrometry (CE‐MS) in the past few years. This review provides highlights of recent advances in CE‐MS for proteomics research, including a short introduction to top‐down mass spectrometry and native mass spectrometry (native MS), as well as a detailed overview of CE methods. Both the potential and limitations of these methods for the analysis of proteins and peptides in synthetic and biological samples and the challenges of CE methods are discussed, along with perspectives about the future direction of CE‐MS. @ 2019 Wiley Periodicals, Inc. Mass Spec Rev 00:1–16, 2019.     

On the stability of non-conservative plane mass loaded beam structures (static approach with the load-distribution method)

Stability problems can generally be regarded as kinetic problems since it is a matter of investigating the behaviour of a disturbance-induced motion away from the equilibrium position. Loading, mass distribution, frictional forces and the nature of the disturbance are thereby of importance. For most conservative problems a simpler calculation can be applied using the static instead of the kinematic equilibrium. For the static stability criterion, the methods of energetic and force equilibrium are available. In the absence of non-conservative problems the kinematic stability criterion is commonly applied.

This work shows that, when applying the load-distribution method a number of solutions for non-conservative mass loaded systems can be found. Thereby, the static stability criterion is used under the prerequisite of infinitesimal deformations.