Sodium ion attachment reactions in an ion trap mass spectrometer

The capabilities of ion traps to perform attachment reactions with alkali cations using classical scanning sequences have been exploited here with an ion trap mass spectrometer equipped with an external ion source to generate the reagent Na(+) ions. Kinetic studies have shown that, as expected, the attachment efficiency is very high, near-collision efficiency, and illustrate how the present method is particularly well suited for ion trap mass spectrometers. The large adaptability of the experimental conditions suggests that a wide range of organic molecules, characterized by a large alkali ion affinity, could be readily detected even at low levels. Applications of sodium ion attachment reactions are illustrated by the detection and characterization of explosives and some of their correlated pyrolytic degradation products. Detection -limits for phthalate compounds are shown to reach the low ng range of injected samples, without any noticeable difficulties in the full scan mode of acquiring mass spectra. Copyright 2000 John Wiley & Sons, Ltd.     

Development of a tabletop time-of-flight mass spectrometer with an ion attachment ionization technique

We report a new type of mass spectrometry based on a time-of-flight mass spectrometer combined with an ion attachment ionization technique (IA-TOF). In contrast to electron ionization mass spectra, IA-TOF mass spectra are not complicated by peaks due to fragmentation of the molecular ion; the adduct ion formed in IA does not fragment. We developed a tabletop IA-TOF system and evaluated its performance by analyzing specimens originally in the gas, liquid, and solid phases. We obtained fragment-free spectra covering a mass range up to m/z 3400 with a mass resolution of about 4700. Our IA-TOF system realizes accurate and versatile real-time mass spectrometry.     

Development of an ion attachment mass spectrometer for direct detection of intermediates in combustion flames

A system with Li+ ion attachment (IA) ionization has been developed for the direct detection of intermediates formed in burning flames by mass spectrometry. Dimethyl ether (DME) among alternative fuels was selected as a test substance to examine the capability of the system. As a result, intermediates generated in a premixed DME-air flame were directly detectable as Li+ adduct ions. By moving the burner on an X-Y stage, spatial distribution profiles of different species, including unburned DME and formaldehyde, were obtained for three types of flames: diffusion, partially premixed, and premixed.     

Selective ionization for elemental analysis with an ion trap mass spectrometer

The ion storage capacity (<10⁶) of ion trap mass spectrometers (ITMS) can sometimes limit the ability to analyze trace components in complex mixtures. We demonstrate here that resonant laser ablation (RLA) can offer a degree of selectivity in the ionization process, thus allowing the preferential accumulation of analyte ions in the trap. Selectivities of 75 and 50, for chromium and iron, respectively, are reported here for RLA of stainless steel in an ITMS. We offer suggestions to improve both the selectivity and the ionization efficiency, relative to the results reported here.     

Development of an ion mobility spectrometer for use in an atmospheric pressure ionization ion mobility spectrometer/mass spectrometer instrument for fast screening analysis

An ion mobility spectrometer that can easily be installed as an intermediate component between a commercial triple-quadrupole mass spectrometer and its original atmospheric pressure ionization (API) sources was developed. The curtain gas from the mass spectrometer is also used as the ion mobility spectrometer drift gas. The design of the ion mobility spectrometer allows reasonably fast installation (about 1 h), and thus the ion mobility spectrometer can be considered as an accessory of the mass spectrometer. The ion mobility spectrometer module can also be used as an independently operated device when equipped with a Faraday cup detector. The drift tube of the ion mobility spectrometer module consists of inlet, desolvation, drift, and extraction regions. The desolvation, drift and extraction regions are separated by ion gates. The inlet region has the shape of a stainless steel cup equipped with a small orifice. Ion mobility spectrometer drift gas is introduced through a curtain gas line from an original flange of the mass spectrometer. After passing through the drift tube, the drift gas serves as a curtain gas for the ion-sampling orifice of the ion mobility spectrometer before entering the ion source. Counterflow of the drift gas improves evaporation of the solvent from the electrosprayed sample. Drift gas is pumped away from the ion source through the original exhaust orifice of the ion source. Initial characterization of the ion mobility spectrometer device includes determination of resolving power values for a selected set of test compounds, separation of a simple mixture, and comparison of the sensitivity of the electrospray ionization ion mobility spectrometry/mass spectrometry (ESI-IMS/MS) mode with that of the ESI-MS mode. A resolving power of 80 was measured for 2,6-di-tert-butylpyridine in a 333 V/cm drift field at room temperature and with a 0.2 ms ion gate opening time. The resolving power was shown to be dependent on drift gas flow rate for all studied ion gate opening times. Resolving power improved as the drift gas flow increased, e.g. at a 0.5 ms gate opening time, a resolving power of 31 was obtained with a 0.65 L/min flow rate and 47 with a 1.3 L/min flow rate for tetrabutylammonium iodide. The measured limits of detection with ESI-MS and with ESI-IMS/MS modes were similar, demonstrating that signal losses in the IMS device are minimal when it is operated in a continuous flow mode. Based on these preliminary results, the IMS/MS instrument is anticipated to have potential for fast screening analysis that can be applied, for example, in environmental and drug analysis.     

Fragmentation of phosphopeptides in an ion trap mass spectrometer

A systematic study of the fragmentation pattern of phosphopeptides in an electrospray (ESI) ion trap mass spectrometer is presented. We show that phosphotyrosine- and phosphothreonine-containing peptides show complicated fragmentation patterns. These phosphopeptides were observed to lose the phosphate moiety in the form of H₃PO₄ and/or HPO₃, but were also detected with no loss of the phosphate group. The tendency to lose the phosphate moiety depends strongly on the charge state. Thus, the highest observed charge state tends to retain the phosphate moiety with extensive fragmentation along the peptide backbone. We also show that phosphoserine-containing peptides have relatively simple fragmentation patterns of losing H₃PO₄. This loss is independent of the charge state. We suggest strategies for the accurate identification of phosphorylation sites using the ion trap mass spectrometer.     

Mass-selected reagent ion chemical ionization and multiple tandem mass spectrometry techniques in an ion trap mass spectrometer for structural analysis

Mass-selected reagent ion chemical ionization (CI) performed in an ion trap instrument is an efficient tool to investigate gas-phase ion reactivities and therefore to find out new and/or optimized applications for structural analysis. For instance, it was shown that the C₃H₆O^{+ .} (58 mass units) molecular ion originated from vinyl methyl ether (VME) should necessarily be used alone (i.e. unit-mass selected) to produce significant diagnostic-ions for double bond location in aliphatic alkenes. Regarding the assignment of epoxides, the previous NO⁺/CI method was adapted for an optimal use in the trap through isolation of NO⁺ cation from N₂O (instead of NO) plasma and production of the acylium diagnostic-ions via CID of [M − H]⁺ formed by NO⁺-induced hydride abstraction. New alkylation ion-products, e.g. RCH = O⁺-al , were also found to characterize isomeric epoxides as a result of either an initial electrophilic addition of the C₂H₅⁺ cation (with saturated epoxides) or a methyl-transfer from [VME]^{+ .} (with α,β-unsaturated epoxides). The multiple tandem mass spectrometry (MSⁿ) capabilities of the ion trap were essential to achieve reagent ion mass-selection, structural assignment of the diagnostic-ions, or to provide further selectivity. © 1997 John Wiley & Sons, Ltd.     

Thermal analysis—mass spectrometer computer system and its application to the evolved gas analysis of green river shale and lunar soil samples

A thermal analysis—mass spectrometer system controlled by a computer has been developed and successfully used in the analysis of a wide variety of geochemical samples. The TA—MS computer system provides a very powerful analytical tool for the determination of volatile species released from samples over a very wide temperature and sample-size range. Use of a small laboratory computer and magnetic-tape storage units permits large quantities of analytical information to be handled and easily retrieved. The rapid scan capabilities of the quadrupole mass spectrometer operating under computer control are especially useful for following the rapidly changing composition of the evolved gases released from samples during heating under vacuum conditions. Samples of volatile-rich Green River shale and two lunar soils have been analyzed to show the utility of the TA—MS computer system.     

Temperature calibration of a mass spectrographic evolved gas analysis system

Because of the vacuum used in mass spectrographic evolved gas analysis, the usual effects of temperature lag between actual and apparent sample temperatures are exaggerated. Factors contributing to this temperature difference are discussed. The melting point of various metals in the range 110–1100°C are used to obtain insights and estimates regarding these temperature discrepancies at different heating rates, utilizing a variety of sample holders. In general, if the sample is in good contact with the heated supporting surface, the agreement between the observed and reported equilibrium melting temperatures is good at heating rates of ? ～ 20°C min. At higher heating rates the differences become larger (?10°C) and the effect increases with increasing temperature of melting. For sample holders which are not in good contact with the sample, hot spots can develop at high temperatures due to unequal thermal radiation. Under these circumstances the apparent melting point can be considerably lower than the actual equilibrium temperature and less dependent upon heating rate.     

Phase-enhanced selective ion ejection in an orbitrap mass spectrometer

The mass resolution achieved in selective ion isolation using resonance excitation is usually limited by the frequency resolution of the ac waveform and by unintended off-resonance excitation. A new method of phase-enhanced selective ion ejection based on broadband dipolar excitation and ion ejection applicable to the Orbitrap is described and shown to allow an isolation resolution of 28,400. The method is calculated to be able to provide a mass resolution for ion ejection of up to 100,000.     

Coupling of an atmospheric-samling ion source with an ion-trap mass spectrometer

An atomospheric-sampling glow-discharge ionization source has been interfaced with an ion-trap mass spectrometer. Under optimum conditions, the efficiency of ion injection is 1–5%. Several factors have a significant effect on the ion injection efficiency, including the voltages on the three-element lens system situated between the ion-source exit and the ion-trap entrance end-cap, the pressure of the bath gas present in the ion-trap vacuum housing, the nature of the bath gas and the amplitude of the radiofrequency voltage applied to the ring electrode during ion injection. Collision-induced dissociation (and electron detachment from anions) is also observed for some ions on injection, depending on the conditions. The most important experimental variables in determining the extent to which dissociation (or electron detachment) occurs are the nature of the bath gas, the bath gas presure and the radiofrequency voltage applied to the ring electrode during injection. These effects are illustrated with data obtained for polyatomic anions injected from the golw-discharge ion source.     

Evolved gas analysis-mass spectrometry using skimmer interface and ion attachment mass spectrometry

Summary A new EGA-MS instrument consisted of a combination of skimmer interface with no change of evolved gaseous species and IAMS (Ion Attachment Mass Spectrometry) with no fragmentation during the ionization has been developed successfully. As its application of evolved gaseous species from PVA as firing process of alumina ceramics binder, the method has indicated detection of gaseous species which have not been detected with Py-GC-MS.     

Quadrupole mass spectrometer for residual gas analysis and SIMS application

Summary A combined secondary ion optics has been developed which includes both the ion source for residual gas analysis and the secondary ion optics for Secondary Ion Mass Spectrometry (SIMS). The change from one mode to the other can be done by changing only the electric connections without venting the vacuum chamber. The presented combination of the two methods allows the interpretation of SIMS spectra with higher reliability.     

A secondary ion microprobe ion trap mass spectrometer

An ion trap mass analyzer has been attached to an organic secondary ion microprobe. A pressure differential >100 can be maintained between the ion trap and microprobe. The well-focused secondary ion beam can transit a small (2 mm) diameter tube, but gas flow from ion trap to microprobe is impeded. This pressure differential allows the microprobe to retain imaging capability. Ion trap and microprobe data systems are integrated by taking advantage of the highly reproducible periodicity of the ion trap operating in resonant ejection mode and asynchronous signal and data acquisition afforded by commercially available interface cards. Secondary ion mass spectra and images obtained indicate an approximately 10-fold improvement in sensitivity, although preliminary evidence indicates low (<1%) trapping efficiency. Image data acquisition using the ion trap for mass analysis requires at least 10 times as much time compared to using a quadrupole mass filter because the mass-selected instability mode is used for mass analysis, i.e., mass resolution in the ion trap is not continuous as it is in the quadrupole.     

Evaluation of small mass spectrometer systems for permanent gas analysis

This work is aimed at understanding the aspects of designing a miniature mass spectrometer (MS) system. Several types of small MS systems are evaluated and discussed, including linear quadrupole, quadrupole ion trap, time of flight, and sector. Analysis of hydrogen, helium, oxygen, and argon in a nitrogen background with the concentrations of the components of interest ranging from 0 to 5000 parts per million (ppm). The performance of each system in terms of accuracy, precision, limits of detection, response time, recovery time, scan rate, size, and weight is assessed. The relative accuracies of the systems varied from <1% to approximately 40% with an average below 10%. Relative precisions varied from 1% to 20%, with an average below 5%. The detection limits had a large distribution, ranging from 0.2 to 170 ppm. The systems had a diverse response time ranging from 4 to 210 s, as did the recovery time with a 6-to-210-s distribution. Most instruments had scan times near 1 s; however, one instrument exceeded 13 s. System weights varied from 9 to 52 kg and sizes ranged from 15 x 10(3) cm3 to 110 x 10(3) cm3. A performance scale is set up to rank each system, and an overall performance score is given to each system.     

Applications of evolved gas analysis Part 2: EGA by mass spectrometry

The analytical applications of the evolved gas analysis (EGA) performed by mass spectrometry, for the period extending from 2001 to 2004, are collected in this review. By this technique, the nature of volatile products released by a substance subjected to a controlled temperature program is on-line determined, with the possibility to prove a supposed reaction, either under isothermal or under heating conditions.     

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.