Mass Spectroscopy Instrument Research Articles

Electron Impact–Mass Spectrometry Fingerprinting and Chemometrics for Rapid Assessment of Authenticity of Edible Oils Based on Fatty Acid Profiling

A new methodology is described herein that provides an experimentally simple, rapid, and cost-effective mass fingerprinting method for the assessment of edible oil authentication based on their fatty acid methyl ester (FAMEs). This analytical approach is based on the application of electron impact (EI) ionization–mass spectrometry (MS) without chromatographic separation, followed by the treatment of the spectral data via chemometrics analysis, linear discriminant analysis (LDA), principal component analysis (PCA), soft independent modeling of class analogies (SIMCA), and hierarchical cluster analysis (HCA). This fingerprinting analysis was applied by using a gas chromatography–mass spectroscopy instrument, without chromatographic column usage and ion identification; therefore, each measurement lasted about 1 min. All multivariate analyses provided excellent discriminations between the edible oil clusters with low classification error. LDA models constructed with six predictors and a total of 100% of edible oil samples from different brands were correctly classified. Furthermore, no misclassification was reported for the discriminant analysis in supervised SIMCA models with an accuracy of 95%. Thus, the present results pointed to the successful application of such methodology to detect, for the first time, authentication of the edible oils.

Ultra high vacuum high precision low background setup with temperature control for thermal desorption mass spectroscopy (TDA-MS) of hydrogen in metals

In this work, a newly developed UHV-based high precision low background setup for hydrogen thermal desorption analysis (TDA) of metallic samples is presented. Using an infrared heating with a low thermal capacity enables a precise control of the temperature and rapid cool down of the measurement chamber. This novel TDA-set up is superior in sensitivity to almost every standard hydrogen analyzer available commercially due to the special design of the measurement chamber, resulting in a very low hydrogen background. No effects of background drift characteristic as for carrier gas based TDA instruments were observed, ensuring linearity and reproducibility of the analysis. This setup will prove to be valuable for detailed investigations of hydrogen trapping sites in steels and other alloys. With a determined limit of detection of 5.9×10−3µgg−1 hydrogen the developed instrument is able to determine extremely low hydrogen amounts even at very low hydrogen desorption rates. This work clearly demonstrates the great potential of ultra-high vacuum thermal desorption mass spectroscopy instrumentation.

Constructing a mass measurement error surface to improve automatic annotations in liquid chromatography/mass spectrometry based metabolomics

Estimation of mass measurement accuracy is an elementary step in the application of mass spectroscopy (MS) data towards metabolite annotations and has been addressed several times in the past. However, the reproducibility of mass measurements over a diverse set of analytes and in variable operating conditions, which are common in high-throughput metabolomics studies, has, to the best of our knowledge, not been addressed so far. A method to automatically extract mass measurement errors from a large data set of measurements made on a quadrupole time-of-flight (QTOF) MS instrument has been developed. The size of the data processed in this study has enabled us to use a statistical data driven approach to build a model which reliably predicts the confidence interval of the absolute mass measurement error based on individual ion peak conditions in a fast, high-throughput manner. We show that our model predictions are reproducible in external datasets generated in similar, but not identical conditions, and have demonstrated the advantage of our approach over the common practice of fixed mass measurement error limits. Outlined is an approach which can promote a more rational use of MS technology by automatically evaluating the absolute mass measurement error based on the individual peak conditions. The immediate application of our method is integration in high-throughput peak annotation pipelines for database searches.

Recent developments in instrumentation of microwave plasma sources for optical emission and mass spectrometry: Tutorial review

This paper reviews the most common methods of generation of plasmas using microwaves with special emphasis on recently developed microwave plasma (MWP) sources for analytical applications. The art and science of microwave plasma optical and mass spectroscopy instrumentation (MWP-OES/MS), and the applications are briefly presented, including very recent advances in the field as of 2012. The design and operation of MWPs is discussed to provide a basic understanding of the most important selection criteria when designing MWP systems. The various plasma generation systems described include single-electrode capacitive microwave plasmas, electrodeless inductively coupled plasmas, multi-electrode systems energized with stationary or rotating fields. We also discuss various technical realizations of MWP sources for selected applications. Examples of technical realizations of plasmas in closed structures (cavities), in open structures (surfatrons, planar plasma sources), and in magnetic fields (Hammer cavity) are discussed in detail. Finally, we mention micro- and mini-discharges as convenient sources for miniaturized spectrometric systems. Specific topics include fundamental aspects of MWP, i.e., recent advances in the construction of analytical MWPs (coaxially coupled cavities, strip-line technology, multi-point energizing, power combining, rotating field-excited plasmas), operational characteristics, analytical characteristics and applications. Special reference is made to coupling with OES for determination of chromatographic effluents and particle sizing. The developments in elemental and molecular MS applications in both low-power and high-power MWPs are also discussed.

Direct mass analysis of neutral molecules by superconductivity

Dissociation related to ion collision reactions produces neutral fragments in addition to ionic fragments, and the ability to analyze both neutral and ionic fragments is crucial for fully understanding chemical reactions in the gas phase. However, conventional mass spectroscopy (MS) instruments are unable to directly analyze multiple neutral fragments without reionization. This inability is called “ neutral loss.” We report the first tandem MS instrument realized by a kinetic-energy-sensitive cryodetector (a superconducting tunnel junction operated in the Giaever mode) as the second mass separation (KEMS) to quantitatively analyze multiple fragment molecules, either neutral or ionic, in a keV kinetic energy range. The performance of the MS/KEMS instrument was examined using the collisions of singly charged acetone or acetyl precursors with a Xe target. These singly charged ions undergo either collisionally activated dissociation (CAD) or electron transfer dissociation (ETD), including a dissociation path of ABA + + e → ABA* → A + B + A or AB + A, which produces neutral fragments only. Our approach is able to determine the branching ratios of the competing CAD and ETD processes and may provide a method to overcome the neutral loss.

Estrogen and Fracture Risk in Men

Estrogen and Fracture Risk in Men

Kinetic Inductance Detectors for Mass Spectroscopy

Mass Spectroscopy (MS) is a powerful analysis tool used for the study of DNA and Proteins. Recently, Time of Flight (ToF) MS instrumentation based on superconductive detectors, namely Transition Edge Sensors (TES) or Superconducting Tunnel Junctions (STJ), have been proposed because they feature a good efficiency even for high masses molecules, which have very low speed. This is due to the fact that both STJ and TES provide a signal that is proportional to the kinetic energy rather than the speed. However, TES and STJ require a low operating temperature (0.1 K) and are relatively slow, which in a ToF-MS translates directly to degraded mass resolution. We propose a different type of detector: the Kinetic Inductance Detector, which has been successfully investigated as an ultra-fast and ultra-sensitive optical detector. This detector has a very fast time response (sub ns), thus providing a very good mass resolution, and shares with the other superconductive detectors the independence on the mass value. Moreover, it could operate at higher temperature (in the 2-4 K range). We have investigated different configurations of kinetic inductance detectors for MS, alone and in combination with Josephson devices, and report on the expected performances.

Proteomics—Application to the Brain

Proteomics is an experimental approach to explain the information contained in the genomic sequences in terms of the structure, function, and control of biological processes and pathways. The proteome is the quantitative expression profile of a cell, an organism, or a tissue under exactly defined conditions. The systematic separation, identification, and characterization of proteins of the nervous system offer a basis for research trying to elucidate the mechanisms of neurodegenerative diseases. The studies of neurodegenerative diseases, on the basis of molecular phenotypes, lead to a new understanding of neurodegeneration. Parkinson's disease (PD) and Alzheimer's disease (AD) are the most prevalent neurodegenerative disorders affecting the aging of human brain. Several proteomics approaches help in the analysis of brain samples. Separation is done either directly on the protein basis using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), one-dimensional polyacrylamide gel electrophoresis (1D-PAGE), or comprehensive one-dimensional or multidimensional liquid phase based separation techniques (1D/MD-LC). For quantification analysis, several approaches, such as metabolic isotope labeling or chemical labeling are described. New developments in mass spectroscopy (MS) instrumentation focus on the methods that introduce as many peptide ions into the mass spectrometer as possible, as well as ways to manipulate the ion population so that the lower-abundance species can be measured exclusively in a complex mixture. It becomes more and more apparent that in the near future, the most powerful technology for the comprehensive analysis of complex protein mixtures will be a combination of multidimensional fractionation and advanced MS instrumentation.

Differential phosphoprofiles of EGF and EGFR kinase inhibitor-treated human tumor cells and mouse xenografts

The purpose of this phospho-proteomics study was to demonstrate the broad analysis of cellular protein phosphorylation in cells and tissue as a means to monitor changes in cellular states. As a cancer model, human tumor-derived A431 cells known to express the epidermal growth factor receptor (EGFR) were grown as cell cultures or xenograft tumors in mice. The cells and tumor-bearing animals were subjected to treatments including the EGFR-directed protein kinase inhibitor PK166 and/or EGF stimulation. Whole cell/tissue protein extracts were converted to peptides by using trypsin, and phosphorylated peptides were purified by an affinity capture method. Peptides and phosphorylation sites were characterized and quantified by using a combination of tandem mass spectroscopy (MS) and Fourier transform MS instrumentation (FTMS). By analyzing roughly 106 cell equivalents, 780 unique phosphopeptides from approx 450 different proteins were characterized. Only a small number of these phosphorylation sites have been described previously in literature. Although a targeted analysis of the EGFR pathway was not a specific aim of this study, 22 proteins known to be associated with EGFR signaling were identified. Fifty phosphopeptides were found changed in abundance as a function of growth factor or drug treatment including novel sites of phosphorylation on the EGFR itself. These findings demonstrate the feasibility of using phospho-proteomics to determine drug and disease mechanisms, and as a measure of drug target modulation in tissue.

Lubrication of Slow Rolling Contacts—The NASA Ball on Plate Tribometer

The NASA Ball on Plate Tribometer was built for the investigation of boundary lubricated rolling. Its contact conditions are easily calculated, and can be adjusted to match a range of real hearing applications for stress, surface velocity, pivot, and contact severity. The rig operates under high vacuum at room temperature. Lubricant charge and specimen preparation are well-controlled and well-characterized. Mass spectroscopy instrumentation allows an indication of lubricant degradation during rolling. Other tribological quantities immediately available are contact resistance, friction coefficient, transverse creep, and orbit velocity deficit. Simple specimens allow post-test surface analysis such as FTIR, XPS, microscopy, and profilometry. Here we describe the Tribometer and discuss representative results obtained with liquid, solid, and no lubricant.

Two-dimensional profiling of large tilt angle, low energy boron implanted structure using secondary-ion mass spectrometry

Experimentally determined two-dimensional dopant maps of implants into semiconductors are required for the calibration and verification of process simulation tools used in very large scale integrated (VLSI) circuit design. Direct measurement with currently available techniques is not possible owing to the physical size of the areas in question. Using a specially fabricated structure and a modified secondary-ion mass spectroscopy instrument, it has been possible to measure profiles with high spatial resolution and sensitivity. In this article we present the results of an investigation of a complex boron implant into silicon, as used in advanced VLSI P-type metal–oxide–semiconductor source–drain regions, and compare it with results from process simulators.

Characterization of two resistive anode encoder position sensitive detectors for use in ion microscopy

Both the standard resistive anode encoder (RAE) position sensitive ion detector and a new faster version have been adapted for use with CAMECA IMS-3f/4f imaging secondary-ion mass spectroscopy instruments. Each detector includes a dual microchannel plate image intensifier mounted in front of a resistive anode. The conversion efficiencies of the standard and fast detectors are 60% and 55%, respectively. The high count rates attainable with the fast detector require high strip-current microchannel plates for optimum performance. The mass bias of these detectors is proportional to (mass)1/2 and can be compensated by adjustment of detector supply voltage. The response across the active area of these detectors is uniform to within 3% with the greatest deviations occurring at the periphery. Distortion and pixel-to-pixel bias are negligible with the standard RAE, but noticeable in the prototype of the fast RAE. Software has been developed that corrects pixel-to-pixel bias. The dead times of the standard and fast RAE systems are 4.3±0.1 μs and 330±2 ns which limit practical count rates to about 40 000 and 600 000 Hz, respectively. For many applications, the higher ion arrival rates and dynamic range of the fast RAE imaging system more than compensate for the increased pixel-to-pixel bias and distortion and the small decrease in conversion efficiency.