Exact mass measurement on an electrospray ionization time-of-flight mass spectrometer: error distribution and selective averaging

An automated, accurate and reliable way of acquiring and processing flow injection data for exact mass measurement using a bench-top electrospray ionization time-of-flight (ESI-TOF) mass spectrometer is described. Using Visual Basic programs, individual scans were selected objectively with restrictions on ion counts per second for both the compound of interest and the mass reference peaks. The selected "good scans" were then subjected to two different data-processing schemes ("combine-then-center" and "center-then-average"), and the results were compared at various ion count limit settings. It was found that, in general, the average of mass values from individual scans is more accurate than the centroid mass value of the combined (same) scans. In order to acquire a large number of good scans in one injection (to increase the sampling size for statistically valid averaging), an on-line dilution chamber was added to slow down the typically rapid mass chromatographic peak decay in flow-injection analysis. This simple addition worked well in automation without the need for manual sample dilution. In addition, by dissolving the reference compound directly into the mobile phase, manual syringe filling can be eliminated. Twenty-seven samples were analyzed with the new acquisition and process routines in positive electrospray ionization mode. For the best method found, the percentage of samples with RMS error less than 5 ppm was 100% with repetitive injection data (6 injections per sample), and 95% with single injection data. Afterwards, 31 other test samples were run (with MW ranging from 310 to 3493 Da, 21 samples in ESI+ and 10 in ESI- mode) and processed with similar parameters and 100% of them were mass-calculated to RMS error less than 5 ppm also.     

Negative chemical ionization and accurate mass measurement applications for a linked gas chromatography/Fourier transform infrared spectrometer/Fourier transform mass spectrometer

Summary The analytical utility of a linked GC/FTIR/ FTMS system operating in accurate mass and negative CI modes is demonstrated. In addition to the complementary information derived from IR and MS search results, accurate mass measurement data (average error of 4.2 ppm) is employed in the analysis of a seven component mixture. A post search filter uses accurate mass data to eliminate spectral search results with incorrect elemental compositions. An alternate positive ion EI and negative ion CI GC/IR/MS analysis is also performed on a mixture of substituted phenyl aldehydes and ketones. The reagent gas, ammonia, is introduced by pulsed valve thus minimizing crossover spectral contamination while maximizing spectral resolution. Proton abstraction by the amide produces an intense (M-1)^– for all compounds in the mixture. Molecular weight information from the negative CI data is used in a post search filter to improve the reliability of both IR and MS search results.

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Anwendung der negativen chemischen Ionisation und genauer Massenmessungen für ein gekoppeltes GC/FTIR/FTMS-System

Zusammenfassung Die analytische Anwendbarkeit eines gekoppelten GC/FTIR/FTMS-Systems mit akkurater Massenmessung und NCI-Betrieb wird dargestellt. Zusätzlich zu den komplementären Informationen aus IR- und MS- Bibliothekssuchen werden Daten aus akkuraten Massenmessungen (mittlerer Fehler 4.2 ppm) bei der Analyse einer Mischung aus sieben Komponenten mit herangezogen. Im Anschluß an die Bibliothekssuche eliminiert ein Filter mit Hilfe der akkuraten Massen Ergebnisse mit fehlerhafter Elementarzusammensetzung. Von einer Mischung aus substituierten Phenylaldehyden und -ketonen wird eine Analyse mit alternierender Registrierung von positiven EI- und negativen CI-Spektren durch ein GC/IR/-MS-System ausgeführt. Das Reaktandgas Ammoniak wird über ein gepulstes Ventil zugegeben, um bei maximaler spektraler Auflösung minimale Störung durch Verunreinigung zu erhalten. Durch Abstraktion eines Protons von der Amidfunktion werden von allen Komponenten der Mischung intensive (M-1)-Ionen gebildet. Molekulargewichtsinformationen aus dem NCI-Experiment werden als Filter verwendet, mit dem die Zuverlässigkeit des Suchens in IR- und MS-Datenbanken erhöht werden kann.

     

Gas chromatographic analysis and aerosol mass spectrometer measurement of diesel exhaust particles composition

Aerosol particles have important effects on human health, climate, regional visibility, and the deposition of acidic and toxic substances. The aerosols also have significant pharmaceutical and industrial applications. Trials of gas chromatographic analysis of extracts composition of diesel exhaust particles and aerosol mass spectrometer measurement of diesel exhaust particles composition are introduced in this paper. Usually, organic fraction of automotive exhaust particles are concentrated to 1 mL by Kuderna-Danish concentrator after extracted into dichloromethane by soxhlet extraction. Then, these extracts are analyzed by GC/MS. In the extracts from the diesel exhaust particles, there are over several thousands of components, for example paraffinic hydrocarbons, aromatics, oxygenates and other hydrocarbons.     

Increase in productivity by networking mass spectrometer data systems

Three personal computers (PCs) are linked in an ethernet network using D-Link LenSmart protocol. Resource sharing and data transfer at very high speed between two different gas chromatography/mass spectrometry (GC/MS) data systems are obtained.     

Recent trends in mass spectrometer development

Trends in mass analyzer development are reviewed here with an emphasis on tandem mass spectrometers. The move toward hybridization of conventional mass analyzers to allow additional instrument functionality in tandem mass spectrometry is discussed.     

Calibration of a chemical ionization mass spectrometer for the measurement of gaseous sulfuric acid

The accurate measurement of the gaseous sulfuric acid concentration is crucial within many fields of atmospheric science. Instruments utilizing chemical ionization mass spectrometry (CIMS) measuring H(2)SO(4), therefore, require a careful calibration. We have set up a calibration source that can provide a stable and adjustable concentration of H(2)SO(4). The calibration system initiates the production of sulfuric acid through the oxidation of SO(2) by OH. The hydroxyl radical is produced by UV photolysis of water vapor. A numerical model calculates the H(2)SO(4) concentration provided at the outlet of the calibration source. From comparison of this concentration and the signals measured by CIMS, a calibration factor is derived. This factor is evaluated to be 1.1 × 10(10) cm(-3), which is in good agreement with values found in the literature for other CIMS instruments measuring H(2)SO(4). The calibration system is described in detail and the results are discussed. Because the setup is external to the CIMS instrument, it offers the possibility for future CIMS intercomparison measurements by providing defined and stable concentrations of sulfuric acid.     

Analysis of triacylglycerol hydroperoxides in human lipoproteins by Orbitrap mass spectrometer

Herein, we represent a simple method for the detection and characterization of molecular species of triacylglycerol monohydroperoxides (TGOOH) in biological samples by use of reversed-phase liquid chromatography with a LTQ Orbitrap XL mass spectrometer (LC/LTQ Orbitrap) via an electrospray ionization source. Data were acquired using high-resolution, high-mass accuracy in Fourier-transform mode. Platform performance, related to the identification of TGOOH in human lipoproteins and plasma, was estimated using extracted ion chromatograms with mass tolerance windows of 5 ppm. Native low-density lipoproteins (nLDL) and native high-density lipoproteins (nHDL) from a healthy donor were oxidized by CuSO₄ to generate oxidized LDL (oxLDL) and oxidized HDL (oxHDL). No TGOOH molecular species were detected in the nLDL and nHDL, whereas 11 species of TGOOH molecules were detected in the oxLDL and oxHDL. In positive-ion mode, TGOOH was found as [M + NH₄]⁺. In negative-ion mode, TGOOH was observed as [M + CH₃COO]^–. TGOOH was more easily ionized in positive-ion mode than in negative-ion mode. The LC/LTQ Orbitrap method was applied to human plasma and three molecular species of TGOOH were detected. The limit of detection is 0.1 pmol (S/N?=?10:1) for each synthesized TGOOH.

Utilizing artificial neural networks in matlab to achieve parts-per-billion mass measurement accuracy with a fourier transform ion cyclotron resonance mass spectrometer

Fourier transform ion cyclotron resonance mass spectrometry has the ability to realize exceptional mass measurement accuracy (MMA); MMA is one of the most significant attributes of mass spectrometric measurements as it affords extraordinary molecular specificity. However, due to space-charge effects, the achievable MMA significantly depends on the total number of ions trapped in the ICR cell for a particular measurement, as well as relative ion abundance of a given species. Artificial neural network calibration in conjunction with automatic gain control (AGC) is utilized in these experiments to formally account for the differences in total ion population in the ICR cell between the external calibration spectra and experimental spectra. In addition, artificial neural network calibration is used to account for both differences in total ion population in the ICR cell as well as relative ion abundance of a given species, which also affords mean MMA values at the parts-per-billion level.     

Simultaneous determination of nitrogen and oxygen in metals by vacuum fusion-quadrupole mass spectrometer

Summary Nitrogen and carbon monoxide extracted from metals are determined simultaneously by use of a combination of a vacuum-fusion furnace and a conventional low-resolution (m/ m=56 atm/e=28) quadrupole mass spectrometer without any modification in the ionization chamber. Only ions with excess of kinetic energy are detected at zero ion-accelerating voltage. The peak intensities of N⁺ and C⁺ give a linear log-log relationship to amount of nitrogen and carbon monoxide over the ranges 0.05–600 and 0.1–600g respectively. The limiting ratios are 1/302/CO<1. When the gas extraction curves are measured for a temperature gradient of 20±5°C/min, the N⁺ and C⁺ ion-peaks show characteristic patterns. The method is thus suitable for studying the extraction behaviour and mechanisms of nitrides and oxides and gives information about the decomposition temperature of these compounds and the state of nitrogen and oxygen in metals. The gas extraction curves for a mixed sample of-Si₃N₄ and-Al₂O₃ powder enclosed in a graphite capsule and for various ferro-alloys, are discussed.

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Simultane Analyse von Stickstoff und Sauerstoff in Metallen mittels Vakuum-Heiß-Extraktion und Massenspektrometrie

Zusammenfassung Aus Metallen werden mittels der Vakuum-Heiß-Extraktion Stickstoff und Kohlenmonoxid freigesetzt und simultan mit einem konventionellen Quadrupol-Massenspektrometer niedriger Auflösung (M/M=56 beim/e=28) ohne Modifikation der Ionisationskammer bestimmt. Dadurch, daß keine Ionen-Beschleunigungsspannung angelegt wird, werden nur die Ionen mit überschüssiger kinetischer Energie erfaßt. Die Peak-Intensitäten von N⁺ und C⁺ stehen in doppelt logarithmischer Darstellung in linearer Beziehung zu der Menge Stickstoff und Kohlenstoff (innerhalb der Bereiche 0,05–600g bzw. 0,1–600g). Das N₂/CO-Verhältnis muß zwischen 1/30 und 1 liegen.Bei Messung der Gas-Extraktionskurven mit einer Aufheizgeschwindigkeit von 20±5°C/min zeigen für die N⁺- und C⁺-Peaks charakteristische Muster. Die Methode eignet sich daher für das Studium von Extraktionsverhalten und -mechanismus von Nitriden und Oxiden und liefert Informationen über die Zersetzungstemperatur dieser Verbindungen und die Bindungsform von Stickstoff und Sauerstoff in Metallen. Die Extraktionskurven eines Pulvergemisches von-Si₃N₄ und-Al₂O₃, eingeschlossen in einer Graphitkapsel, und verschiedener Eisenlegierungen wurden diskutiert.

     

Design and calibration of an electrostatic energy analyzer-time-of-flight mass spectrometer for measurement of laser-desorbed ion kinetic energies

The design of a hybrid electrostatic energy analyzer-time-of-flight mass spectrometer for measurement of ion kinetic energies produced by laser desorption ionization is presented. The need for experimental evaluation of the calibration and performance of the instrument is discussed and a novel laser multiphoton ionization technique, which allows experimental calibration of the energy bandpass of the electrostatic energy analyzer, is described. Laser multiphoton ionization at varying electric field strengths also allows the effects of electric field distortions on energy resolution of the instrument to be probed. Measurement of the translational energies of ions produced by 266-nm laser desorption ionization at 48 mJ/cm² of material adsorbed to a stainless steel probe by using this instrument also is presented. Ion translational energies of +19±5, +10±5, and +10±5 eV are found for adsorbed Na⁺, K⁺, and m-xylene M⁺, respectively.     

Dynamic range of mass accuracy in LTQ orbitrap hybrid mass spectrometer

Using a novel orbitrap mass spectrometer, the authors investigate the dynamic range over which accurate masses can be determined (extent of mass accuracy) for short duration experiments typical for LC/MS. A linear ion trap is used to selectively fill an intermediate ion storage device (C-trap) with ions of interest, following which the ensemble of ions is injected into an orbitrap mass analyzer and analyzed using image current detection and fast Fourier transformation. Using this technique, it is possible to generate ion populations with intraspectrum intensity ranges up to 10(4). All measurements (including ion accumulation and image current detection) were performed in less than 1 s at a resolving power of 30,000. It was shown that 5-ppm mass accuracy of the orbitrap mass analyzer is reached with >95% probability at a dynamic range of more than 5000, which is at least an order of magnitude higher than typical values for time-of-flight instruments. Due to the high resolving power of the orbitrap, accurate mass of an ion could be determined when the signal was reliably distinguished from noise (S/Np-p)>2...3).     

Fixation of nitrogen in an electrospray mass spectrometer

The formation of an iron-nitrogen compound in an electrospray ionization instrument is reported. The iron was released from the stainless steel electrospray needle by acetic acid added to displace trifluoroacetic acid and the nitrogen was present as the drying gas. The product is an iron nitride ion, [N(2)FeOH](1+), m/z 100.9438, and is capable of addition to peptides and proteins.     

Trajectory compensation in an autoresonant trap mass spectrometer

The auto-resonant trap mass spectrometer, ART-MS, utilizes electrostatic ion trapping within an anharmonic potential well. Ions are detected after mass selective trap ejection with auto-resonant driving employing only low-power rf electronics. We identify the major limiting factor in the mass resolution of these instruments. Whilst keeping in the spirit of maintaining a rapid scan rate, low cost, lightweight instrument, with minimal required machining tolerances, we introduce a method for much improving the mass resolutions of an ART-MS. The addition of two electrodes has enabled an improvement in the mass resolution by a factor of ～4. The scheme significantly reduces the effects of a finite sized trap and compensates for the influence of radial variation in natural oscillating frequencies within the trap. Compensation can be implemented with a wide range of designs and is not limited by the size of the trap.     

Exact mass measurement of product ions for the structural elucidation of drug metabolites with a tandem quadrupole orthogonal-acceleration time-of-flight mass spectrometer

We herein report upon an approach whereby the interpretation of tandem mass spectrometry spectra can be both expedited and simplified via the accurate mass assignment of product ions utilizing a tandem quadrupole time-of-flight mass spectrometer (QqTOF). The applicability of the QqTOF in the drug metabolism laboratory is illustrated by the elucidation and differentiation of the dissociative pathways for Bosentan and its hydroxylated and demethylated metabolites. Target analyte fragmentation mechanisms were readily achieved by the measurement of product ions with a mass accuracy <5 ppm, possible by single-point internal recalibration using the residual precursor ion as calibrant. Differentiation of both precursor and product ions from nominally isobaric matrix species derived from biological extracts is demonstrated by operation of the QqTOF at resolutions of 8000 (m/Δm_FWHM).     

Claisen rearrangement taking place in the mass spectrometer

Conclusions The Claisen rearrangement of bucharaine and of the aldehyde bucharainal takes place under the conditions of mass spectrometry. At low temperatures inversion predominates and at high temperatures the anomalous rearrangement.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 577–583, September–October, 1970.