Automated electrospray ionization FT-ICR mass spectrometry for petroleum analysis

Analysis of petroleum samples at the molecular level by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) typically requires a prolonged accumulation of ions and/or summing up a large number of scans. Here, a chip-based micro-ESI system (Advion NanoMate, Ithaca, NY) has been successfully automated in combination with FT-ICR MS analysis of petroleum samples. A foil-sealed 96-well glass plate prevents solvent evaporation, with no visible loss of sample after 20 h of continuous operation. Mass spectra obtained from the same sample but taken from different wells after various time delays were very similar. Data from replicate samples in different wells could be combined to enhance mass spectral signal-to-noise ratio and dynamic range. Furthermore, the automated data acquisition eliminates sample carryover, and produces heteroatom class distribution, double-bond equivalents (DBE), and carbon number very similar to those from the conventional (manual) micro-ESI experiments.     

High-pressure ion trap mass spectrometry

The effects of buffer gas pressure on ion trap stability, mass resolution/calibration, and choice of mass scanning are described. Pressure effects were treated phenomenologically by adding a drag term to the ion equations of motion. The resulting collisional damping enlarges the mass-dependent stability region but reduces the region in which mass-selective resonance ejection can be performed. The pressure effects can be reduced by increasing the frequency of the alternating quadrupole field.     

A tuning method for electrically compensated ion cyclotron resonance mass spectrometer traps

We describe a method for tuning electrically compensated ion cyclotron resonance (ICR) traps by tracking the observed cyclotron frequency of an ion cloud at different oscillation mode amplitudes. Although we have used this method to tune the compensation voltages of a custom-built electrically compensated trap, the approach is applicable to other designs that incorporate electrical compensation. To evaluate the effectiveness of tuning, we examined the frequency shift as a function of cyclotron orbit size at different z-mode oscillation amplitudes. The cyclotron frequencies varied initially by ∼12 ppm for ions with low z-mode oscillation amplitudes compared with those with high z-mode amplitudes. This frequency difference decreased to ∼1 ppm by one iteration of trap tuning.     

A combined linear ion trap for mass spectrometry

We propose a novel ion cyclotron resonance ion trap capable of confining ions even at high pressure. The trap consists of three capacitively coupled axial sections, each composed of four circular cross-section rods parallel to the magnetic field axis. Ion confinement along the magnetic field direction is provided by applying the same static voltage to each set of “endcap” rods. As for a two-dimensional quadrupole mass filter, a sufficiently high rf frequency (several MHz) leads to an “effective” electrostatic “pseudopotential” well with a minimum on the trap central axis. Ions are confined radially by the combination of an applied axial static magnetic field and a radially inward-directed electric field resulting from differential rf voltages applied to each set of four rods. Ion confinement properties are revealed from a Paul traplike “stability diagram,” whereas ion trajectories are analyzed in terms of Penning-type ion cyclotron rotation, magnetron rotation, and axial oscillation motional modes. Ion cyclotron frequency increases with the strength of the rf trapping field. Ion magnetron motion becomes stable if the rf voltage is high enough. Therefore, ion trajectories can be stable even in the presence of ion-neutral collisions. Adding an ac potential to a Penning trap should dramatically increase the upper mass detection limit.     

A broad-band FT-ICR Penning trap system for KATRIN

The KArlsruhe TRItium Neutrino experiment KATRIN aims at improving the upper limit of the mass of the electron antineutrino to about 0.2 eV (90% c.l.) by investigating the -decay of tritium gas molecules . The experiment is currently under construction to start first data taking in 2012. One source of systematic uncertainties in the KATRIN experiment is the formation of ion clusters when tritium decays and decay products interact with residual tritium molecules. It is essential to monitor the abundances of these clusters since they have different final state energies than tritium ions. For this purpose, a prototype of a cylindrical Penning trap has been constructed and tested at the Max-Planck-Institute for Nuclear Physics in Heidelberg, which will be installed in the KATRIN beam line. This system employs the technique of Fourier-Transform Ion-Cyclotron-Resonance in order to measure the abundances of the different stored ion species.     

High mass accuracy and high mass resolving power FT-ICR secondary ion mass spectrometry for biological tissue imaging

Biological tissue imaging by secondary ion mass spectrometry has seen rapid development with the commercial availability of polyatomic primary ion sources. Endogenous lipids and other small bio-molecules can now be routinely mapped on the sub-micrometer scale. Such experiments are typically performed on time-of-flight mass spectrometers for high sensitivity and high repetition rate imaging. However, such mass analyzers lack the mass resolving power to ensure separation of isobaric ions and the mass accuracy for elemental formula assignment based on exact mass measurement. We have recently reported a secondary ion mass spectrometer with the combination of a C₆₀ primary ion gun with a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) for high mass resolving power, high mass measurement accuracy, and tandem mass spectrometry capabilities. In this work, high specificity and high sensitivity secondary ion FT-ICR MS was applied to chemical imaging of biological tissue. An entire rat brain tissue was measured with 150 μm spatial resolution (75 μm primary ion spot size) with mass resolving power (m/Δm _50%) of 67,500 (at m/z 750) and root-mean-square measurement accuracy less than two parts-per-million for intact phospholipids, small molecules and fragments. For the first time, ultra-high mass resolving power SIMS has been demonstrated, with m/Δm _50%?>?3,000,000. Higher spatial resolution capabilities of the platform were tested at a spatial resolution of 20 μm. The results represent order of magnitude improvements in mass resolving power and mass measurement accuracy for SIMS imaging and the promise of the platform for ultra-high mass resolving power and high spatial resolution imaging.

离子阱颗粒质谱研究进展

随着质谱技术的不断发展,对超高质量颗粒物质的分析已经成为质谱领域研究的一个重要方向.离子阱颗粒质谱(particle ion trap mass spectrometry)作为用于完整颗粒质量分析的有利工具,拓展了质谱技术在巨大颗粒物质量分析中的应用范围.本文对离子阱颗粒质谱仪器的研究进展及其在各个领域的应用进行了综述,并展望了离子阱颗粒质谱未来的发展趋势.     

Damping effects in Penning trap mass spectrometry

Collisions of ions with residual gas atoms in a Penning trap can have a strong influence on the trajectories of the ions, depending on the atom species and the gas pressure. We report on investigations of damping effects in time-of-flight ion-cyclotron resonance mass spectrometry with the Penning trap mass spectrometers ISOLTRAP at ISOLDE/CERN (Geneva, Switzerland) and SHIPTRAP at GSI (Darmstadt, Germany). The work focuses on the interconversion of the magnetron and cyclotron motional modes, in particular the modification of the resonance profiles for quadrupolar excitation due to the damping effect of the residual gas. Extensive experiments have been performed with standard and Ramsey excitation schemes. The results are in good agreement with predictions obtained by analytical continuation of the formulae for the undamped case.     

Characterization of orphan monooxygenases by rapid substrate screening using FT-ICR mass spectrometry

Characterization of orphan enzymes, for which the catalytic functions and actual substrates are still not elucidated, is a significant challenge in the postgenomic era. Here, we describe a general strategy for exploring the catalytic potentials of orphan monooxygenases based on direct infusion analysis by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). Eight cytochromes P450 from Bacillus subtilis were recombinantly expressed in Escherichia coli and subjected to a reconstitution system containing appropriate electron transfer components and many potential substrates. The reaction mixtures were directly analyzed using FT-ICR/MS, and substrates of the putative enzymes were readily identified from the mass spectral data. This allowed identification of previously unreported CYP109B1 substrates and the functional assignment of two putative cytochromes P450, CYP107J1 and CYP134A1. The FT-ICR/MS-based approach can be easily applied to large-scale screening with the aid of the extremely high mass resolution and accuracy.     

Analysis of MALDI FT-ICR mass spectrometry data: A time series approach

Matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry is a technique for high mass-resolution analysis of substances that is rapidly gaining popularity as an analytic tool. Extracting signal from the background noise, however, poses significant challenges. In this article, we model the noise part of a spectrum as an autoregressive, moving average (ARMA) time series with innovations given by a generalized gamma distribution with varying scale parameter but constant shape parameter and exponent. This enables us to classify peaks found in actual spectra as either noise or signal using a reasonable criterion that outperforms a standard threshold criterion.     

Recent developments in analytical ion trap mass spectrometry

The current status of quadrupole ion trap mass spectrometry is reviewed, with particular emphasis on liquid chromatographic coupling, membrane inlet introduction, laser desorption/ionisation and selective chemical ionisation. The flexibility, high sensitivity and multi-stage tandem mass spectrometric capability of the quadrupole ion trap are all illustrated.     

Ion trap mass spectrometry: a personal perspective

This paper is a personal perspective of the commercial development of the three-dimensional quadrupole ion trap mass spectrometer. Early ion trap invention and development which dates back to 1953, is described. The development of the ion trap is traced through three ages with the last age being where commercial development takes place. Key technical breakthroughs in ion trap technology and commercialization are presented and described up to the present time.     

An introduction to quadrupole-time-of-flight mass spectrometry

A brief introduction is presented to the basic principles and application of a quadrupole-time-of-flight (TOF) tandem mass spectrometer. The main features of reflecting TOF instruments with orthogonal injection of ions are discussed. Their operation and performance are compared with those of triple quadrupoles with electrospray ionization and matrix-assisted laser desorption/ionization (MALDI) TOF mass spectrometers. Examples and recommendations are provided for all major operational modes: mass spectrometry (MS) and tandem MS (MS/MS), precursor ion scans and studies of non-covalent complexes. Basic algorithms for liquid chromatography/MS/MS automation are discussed and illustrated by two applications.     

Enhanced mass resolution tandem mass spectrometry method for 2,3,7,8-tetrachlorodibenzo-p-dioxin detection with ion trap mass spectrometry using high damping gas pressure

Damping gas flow was optimized for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) determination using ion trap mass spectrometer. A tandem mass spectrometry (MS-MS) method with better than unit-mass resolution (mass width, 0.3 u) was developed at a damping gas flow of 1.5 ml/min and a collision-induced dissociation (CID) voltage of 3.30 V. The relative standard deviation (R.S.D.) at the enhanced resolution was 2.9% in 24 h of consecutive injections. The detection limit was significantly improved because the efficiency of both precursor ion trapping and fragmentation increased with the damping gas flow. Product ion yield was 4.5 times higher and limit of detection was 3.2 times lower than at the default flow (0.3 ml/min and 1.65 V).     

Boundary-effect activated dissociation in ion trap tandem mass spectrometry

The potential of boundary-effect activated dissociation (BAD) in ion trap tandem mass spectrometry (MS/MS) is discussed. Several classes of compounds were investigated and the BAD product ion tandem mass spectra were compared with those from collisionally activated dissociation (CAD) where an auxilliary r.f. ‘tickle’ voltage is used. The energy deposition in BAD MS/MS is generally lower than that for optimized CAD, but the experiments are easier to perform. An example of the BAD MS/MS of C₁₀ alkylbenzenes and benzothiophene in diesel fuel using gas chromatographic introduction and predicted r.f. and d.c. voltages is presented.     

Low pressure chemical ionization in ion trap mass spectrometry

This article presents the specificities of low pressure chemical ionization in ion trap mass spectrometry. One main feature is the ability to perform chemical ionization with liquid reagents as readily as with "conventional" gases (methane, isobutane and ammonia). The reactivities and analytical applications of gas and liquid reagents are summarized from literature data and are compared when possible.