Secular frequency scanning is implemented and characterized using both a benchtop linear ion trap and a miniature rectilinear ion trap mass spectrometer. Separation of tetraalkylammonium ions and those from a mass calibration mixture and from a pesticide mixture is demonstrated with peak widths approaching unit resolution for optimized conditions using the benchtop ion trap. The effects on the spectra of ion trap operating parameters, including waveform amplitude, scan direction, scan rate, and pressure are explored, and peaks at black holes corresponding to nonlinear (higher-order field) resonance points are investigated. Reverse frequency sweeps (increasing mass) on the Mini 12 are shown to result in significantly higher ion ejection efficiency and superior resolution than forward frequency sweeps that decrement mass. This result is accounted for by the asymmetry in ion energy absorption profiles as a function of AC frequency and the shift in ion secular frequency at higher amplitudes in the trap due to higher order fields. We also found that use of higher AC amplitudes in forward frequency sweeps biases ions toward ejection at points of higher order parametric resonance, despite using only dipolar excitation. Higher AC amplitudes also increase peak width and decrease sensitivity in both forward and reverse frequency sweeps. Higher sensitivity and resolution were obtained at higher trap pressures in the secular frequency scan, in contrast to conventional resonance ejection scans, which showed the opposite trend in resolution on the Mini 12. Mass range is shown to be naturally extended in secular frequency scanning when ejecting ions by sweeping the AC waveform through low frequencies, a method which is similar, but arguably superior, to the more usual method of mass range extension using low q resonance ejection.
A method is reported for evaluating ion trap mass analyzers by selection of operating conditions under which both boundary and resonance ejection peaks occur in a single mass scan. The choice of frequency and amplitude of the auxiliary waveform applied for resonance ejection can be such as to produce a resonance ejection mass spectrum with unit resolution or, under selected conditions, signals attributable to both boundary and resonance ejection in a single mass scan. The contrasting mass resolution associated with these two ejection processes is evident in these data. The co-occurrence of the two ejection phenomena is ascribed to the effects of higher-order fields; it is more marked in some rectilinear ion traps (RITs) than in other nominally identical devices, leading to the possibility of using it to compare individual mass analyzers in multiplexed instruments. The method is used to compare multiple ion traps driven by the same RF signal in a fully-multiplexed mass spectrometer, composed of parallel ion source/mass analyzer/detector channels each housed in one quadrant of a specialized vacuum chamber. 相似文献
Initial results obtained using a new electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FTICR) mass spectrometer operated at a magnetic field 11.5 tesla are presented. The new instrument utilized an electrostatic ion guide between the ESI source and FTICR trap that provided up to 5% overall transmission efficiency for light ions and up to 30% efficiency for heavier biomolecules. The higher magnetic field in combination with an enlarged FTICR ion trap made it possible to substantially improve resolving power and operate in a more robust fashion for large biopolymers compared to lower field instruments. Mass resolution up to 106 has been achieved for intermediate size biopolymers such as bovine ubiquitin (8.6 kDa) and bovine cytochrome c (12.4 kDa) without the use of frequency drift correction methods. A mass resolution of 370,000 has been demonstrated for isotopically resolved molecular ions of bovine serum albumin (66.5 kDa). Comparative measurements were made with the same spectrometer using a lower field 3.5-tesla magnet allowing the performance gains to be more readily quantified. Further improvements in pumping capacity of the vacuum system and efficiency of ion transmission from the source are expected to lead to further substantial sensitivity gains. 相似文献
Collision-activated dissociation spectra of dimethyl phosphonate and dimethyl phosphite ions were measured as a function of the amplitude of a supplementary AC voltage applied across the end-caps of an ion-trap mass spectrometer. These spectra yield breakdown graphs which bear a close resemblance to those obtained by varying collision energy in a triple-quadrupole mass spectrometer operating under multiple-collision conditions. Variation in the time of excitation at the resonance frequency provides an alternative route to breakdown graphs. The results demonstrate that energy deposition occurs via multiple activating collisions in the ion trap. Maximum energy deposition observed is somewhat smaller under normal operating conditions in the ion trap than in the triple-quadrupole mass spectrometer. 相似文献
A Fourier transform operating mode is applied to an ion trap. The trap is truncated at 2r(0) and presents unwanted defects that induce confinement electric-field non-linearities. Ion axial secular-motion spectrum is examined by experiments near the resonance line beta(z) = 0.5. Ion-loss processes and ion axial-motion peak splitting are observed. In the non-linear ion trap, the ion-motion frequency depends on its initial conditions in position and velocity. This brings an enlargement of the motion-frequency peak and limits the resolution. With a 2r(0) truncated ion trap, the Fourier transform ion trap mass spectrometer (FTIT-MS) leads experimentally to a mass resolution of about 4000 at 130 u. 相似文献
A method for the confinement of ions at 760 Torr and room temperature is described. We have recently shown that a cylindrical-geometry high-field asymmetric waveform ion mobility spectrometer (FAIMS), which utilizes an ion separation technique based on the change in ion mobility at high electric fields, focuses ions in two dimensions. This article describes a FAIMS device in which the focusing is extended to three dimensions (i.e. ion trap). Characterization of the ion trap was carried out using a laboratory-constructed time-of-flight mass spectrometer. The half-life of a m/z 380 ion in the trap was determined to be 5 ms. 相似文献
Techniques are presented for mass-selective ion manipulation over a wide mass range in a three-dimensional quadrupole. The methods use an auxiliary, low-amplitude radio-frequency signal applied to the endcap electrodes. This signal is either held at a single frequency as the fundamental radio-frequency trapping amplitude is ramped or swept over a frequency range while the fundamental radio-frequency trapping amplitude is held at a fixed level. Ion isolation and ejection are demonstrated for ions formed within the ion trap using electron ionization and for ions injected into the ion trap formed either by an air-sustained glow discharge or by electrospray. Mass-selective ion ejection is used to reduce matrix-ion-induced space charge during ion injection, thereby producing signal enhancement for the detection of 2, 4, 6-trinitrotoluene in air. Mass-selective isolation of ions with mass-to-charge ratios above the normal operating range (m / z 650) for the ion trap is also demonstrated after injection of myoglobin ions formed via electrospray. 相似文献
The use of a linear or two-dimensional (2-D) quadrupole ion trap as a high performance mass spectrometer is demonstrated. Mass analysis is performed by ejecting ions out a slot in one of the rods using the mass selective instability mode of operation. Resonance ejection and excitation are utilized to enhance mass analysis and to allow isolation and activation of ions for MS(n) capability. Improved trapping efficiency and increased ion capacity are observed relative to a three-dimensional (3-D) ion trap with similar mass range. Mass resolution comparable to 3-D traps is readily achieved, including high resolution at slower scan rates, although adequate mechanical tolerance of the trap structure is a requirement. Additional advantages of 2-D over 3-D ion traps are also discussed and demonstrated. 相似文献
Proceeding from the pseudopotential-well approximation for ion motion in a quadrupole ion trap, mathematical expressions are derived to describe the excitation amplitude of an ion packet at a given mass-to-charge ratio. Ion-neutral collisions are incorporated to describe the damping of ion trajectories and to describe the distribution of individual ion trajectories about a mean amplitude for the ion packet. The rate of increase of the amplitude during scanning is related to expressions that describe the amplitude dispersion of the ions at the time of ejection from the trap, which is operating in a resonance ejection scanning mode to describe the temporal line width of the ejected ion packet. The temporal line width is related to mass resolution under a number of different scanning conditions. Included in the discussion are considerations of the effect on resolution of the resonance excitation voltage, temperature, pressure, noise, and buffer-gas composition. An expression for the maximum possible resolution at high ion mass-to-charge ratios is developed, and these results are compared to an existing theoretical construction. The expressions derived under the pseudopotential-well approximation are further extended to high qz values and compared to experimental data previously published by two other researchers. 相似文献
We report a new hybrid mass spectrometer, which is a combination of a quadrupole ion trap and an orthogonal time-of-flight (TOF) mass spectrometer. This new configuration consists of a collisional-damping chamber (CDC) inserted between an MSn-capable ion trap and a high-mass-accuracy orthogonal-TOF mass spectrometer. Because the CDC converted an ion packet into an energy-focused and quasi-continuous beam, a high mass resolution of over 10,000 and a high mass accuracy of better than 3 ppm were achieved. Moreover, the ratio of the maximum detectable m/z to the minimum detectable m/z, which is referred to here as the mass window, was improved to more than 10. 相似文献
In-trap fragmentation of ions in a hybrid linear ion trap triple quadrupole mass spectrometer occurs at pressures about 5e-5
torr. At these low pressures, efficient fragmentation of heavy ions (such as the singly charged homogenously substituted triazatriphosphorine
of mass 2721.89 Da) can take a long time because of the relatively low collision frequency with the background gas and the
high internal energy content required to produce fragmentation. Increasing the amplitude used for dipolar excitation leads
to loss of the ion upon the quadrupole rods. In the work presented here, the addition of a dc octopolar field to a linear
ion trap is described. The dc octopolar field was created by the addition of four auxiliary electrodes situated between the
quadrupole rods at a distance of 10 mm from the axis. The inclusion of the dc octopolar field was shown to cause the ions’
frequency of motion to shift out of phase with the excitation signal at high radial amplitudes. This resulted in beat-like
trajectories with periods of excitation and de-excitation as the ions’ frequency of motion shifted in and out of phase with
the excitation signal. This led to a reduction in the loss of ions on the quadrupole rods during the excitation process. The
result is an increased fragmentation efficiency relative to the fragmentation efficiency obtained when using an LIT constructed
of round rods only. The inclusion of the dc octopolar field allowed the ion to be fragmented more efficiently in a relatively
short excitation period. 相似文献
In this article, the Poincare-Lighthill-Kuo (PLK) method is used to derive an analytical expression on the stability boundary
and the ion trajectory. A multipole superposition model mainly including octopole component is adopted to represent the inhomogeneities
of the field. In this method, both the motional displacement and secular frequency of ions have been expanded to asymptotic
series by the scale of nonlinear term ε, which represents a weak octopole field. By solving the zero and first-order approximate
equations, it is found that a frequency shift exists between the ideal and nonlinear conditions. The motional frequency of
ions in nonlinear ion trap depends on not only Mathieu parameters, a and q, but also the percentage of the nonlinear field and the initial amplitude of ions. In the same trap, ions have the same mass-to-charge
ratio (m/z) but they have different initial amplitudes or velocities. Consequently, they will be ejected at different time through after
a mass-selective instability scan. The influences on the mass resolution in quadrupole ion trap, which is coupled with positive
or negative octopole fields, have been discussed respectively. 相似文献