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Alan G Marshall - One of the best experts on this subject based on the ideXlab platform.
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elemental composition validation from stored waveform Inverse Fourier Transform swift isolation ft icr ms isotopic fine structure
Journal of the American Society for Mass Spectrometry, 2013Co-Authors: Brian M Ruddy, Gregory T Blakney, Ryan P Rodgers, Christopher L Hendrickson, Alan G MarshallAbstract:Elemental composition assignment confidence in mass spectrometry is typically assessed by monoisotopic mass accuracy. For a given mass accuracy, resolution and detection of other isotopologues can further narrow the number of possible elemental compositions. However, such measurements require ultrahigh resolving power and high dynamic range, particularly for compounds containing low numbers of nitrogen and oxygen (both 15N and 18O occur at less than 0.4 % natural abundance). Here, we demonstrate validation of molecular formula assignment from isotopic fine structure, based on ultrahigh resolution broadband Fourier Transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Dynamic range is enhanced by external quadrupole and internal stored waveform Inverse Fourier Transform (SWIFT) isolation to facilitate detection of low abundance heavy atom isotopologues.
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stored waveform Inverse Fourier Transform swift ion excitation in trapped ion mass spectometry theory and applications
International Journal of Mass Spectrometry and Ion Processes, 1996Co-Authors: Shenheng Guan, Alan G MarshallAbstract:Abstract Stored waveform excitation produced by Inverse Fourier Transformation of a specified magnitude/phase excitation spectrum offers the most general and versatile means for broadband mass-selective excitation and ejection in Penning (FT-ICR) and Paul (quadrupole) ion trap mass spectrometry. Since the last comprehensive review of SWIFT excitation in 1987, the technique has been adopted, modified, and extended widely in both the ICR and quadrupole ion trap communities. Here, we review the principles, variations, algorithms, hardware implementation, and some applications of SWIFT for both ICR and quadrupole ion trap mass spectrometry. We show that the most desirable SWIFT waveform is that optimized to reduce both the time-domain SWIFT maximum amplitude and the amplitude near the start and end of the SWIFT waveform. We examine the “true” magnitude excitation spectrum, obtained by zero-filling and forward Fourier Transforming the SWIFT time-domain waveform, in order to evaluate the trade-off between spectral magnitude uniformity and frequency (mass) selectivity. Apodization of the SWIFT waveform is optimally conducted by smoothing the excitation magnitude spectrum prior to generation of the SWIFT waveform by Inverse FT. When (as for broadband ejection in a quadrupole ion trap) it is important that ions be excited near-simultaneously over a wide mass range, the phase spectrum (before Inverse FT to generate the SWIFT waveform) may be overmodulated or randomly modulated (“filtered noise field”), with the recognition that very substantial non-uniformity in the “true” excitation magnitude spectrum will result.
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stored waveform Inverse Fourier Transform axial excitation ejection for quadrupole ion trap mass spectrometry
Analytical Chemistry, 1993Co-Authors: Shenheng Guan, Alan G MarshallAbstract:A general method for high-resolution ion excitation, ejection, and isolation is developed from linear response theory for resonant dipolar excitation of the axial z-oscillatory motion of ions in a quadrupole (Paul) ion trap operated in rf-only mode. For a spatially uniform dipolar excitation field, the ion z-oscillation amplitude is directly proportional to the amplitude of the Fourier component of the excitation at the axial oscillation frequency of that ion. Thus, one may specify an arbitrary z-motion frequency-domain spectrum by applying a time-domain stored waveform obtained from the Inverse Fourier Transform of the corresponding frequency-domain excitation spectrum. The stored waveform Inverse Fourier Transform (SWIFT) waveform may be tailored for selective ejection or excitation of ions of arbitrary mass-to-charge ratio ranges. The method includes all other possible excitation/ejection waveforms (e.g., single frequency, frequency sweep) as special cases. The effect of collisional damping during excitation is included in the analytical solution of the ion response.
Graham R Cooks - One of the best experts on this subject based on the ideXlab platform.
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direct determination of organic compounds in water at parts per quadrillion levels by membrane introduction mass spectrometry
Analytical Chemistry, 1995Co-Authors: Manish Soni, Philip S. H. Wong, Scott J Bauer, Jon W Amy, Graham R CooksAbstract:Parts-per-quadrillion level detection of toluene and trans-1,2-dichloroethene in water has been achieved on-line, without preconcentration, by employing selective ionization in conjunction with membrane introduction ion trap mass spectrometry. The stored wave form Inverse Fourier Transform technique is used to create broad-band wave forms, notched at the resonance frequencies of analyte ions of interest. A series of such pulses is applied during ionization to eject unwanted ions and store only analyte ions. This capability is used over long ionization times to obtain extraordinarily low detection limits for aqueous solutions of volatile organic compounds, introduced into the ion trap using a silicone membrane located within in a commercially available capillary membrane inlet system
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broad band excitation in the quadrupole ion trap mass spectrometer using shaped pulses created with the Inverse Fourier Transform
Analytical Chemistry, 1993Co-Authors: Randall K Julian, Graham R CooksAbstract:This paper reports on broad-band excitation of ions in the quadrupole ion trap mass spectrometer (ITMS) using shaped pulses. In place of a singlefrequency excitation signal, applied to the end caps of the ITMS, a shaped pulse which excites a broad spectrum of frequencies is used. Shaped pulses are time domain signals created by taking the complex Inverse Fourier Transform of a frequency domain function whose magnitude represents the desired excitation spectrum. In mass spectrometry these signals are termed SWIFT (stored wave form Inverse Fourier Transform) pulses
Jean Laroche - One of the best experts on this subject based on the ideXlab platform.
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synthesis of sinusoids via non overlapping Inverse Fourier Transform
IEEE Transactions on Speech and Audio Processing, 2000Co-Authors: Jean LarocheAbstract:Additive synthesis is a powerful tool for the analysis/modification/synthesis of complex audio or speech signals. However, the cost of wavetable sinusoidal synthesis can become prohibitive for large numbers of sinusoids (more than a few hundred). In that case, techniques based on the Inverse Fourier Transform offer an attractive alternative, being 200-300% more efficient than wavetable synthesis depending on the number of sinusoids. This paper presents an improved technique based on the concatenation of short-term signals obtained by Inverse Fourier Transforms. In contrast to the standard overlap-add technique, the new algorithm requires synthesizing sinusoids in the frequency domain whose time-domain amplitudes vary linearly within the synthesis frame. The technique is shown to achieve higher quality than the standard overlap-add technique, at the cost of a small increase in computation.
Manish Soni - One of the best experts on this subject based on the ideXlab platform.
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direct determination of organic compounds in water at parts per quadrillion levels by membrane introduction mass spectrometry
Analytical Chemistry, 1995Co-Authors: Manish Soni, Philip S. H. Wong, Scott J Bauer, Jon W Amy, Graham R CooksAbstract:Parts-per-quadrillion level detection of toluene and trans-1,2-dichloroethene in water has been achieved on-line, without preconcentration, by employing selective ionization in conjunction with membrane introduction ion trap mass spectrometry. The stored wave form Inverse Fourier Transform technique is used to create broad-band wave forms, notched at the resonance frequencies of analyte ions of interest. A series of such pulses is applied during ionization to eject unwanted ions and store only analyte ions. This capability is used over long ionization times to obtain extraordinarily low detection limits for aqueous solutions of volatile organic compounds, introduced into the ion trap using a silicone membrane located within in a commercially available capillary membrane inlet system
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selective injection and isolation of ions in quadrupole ion trap mass spectrometry using notched waveforms created using the Inverse Fourier Transform
Analytical Chemistry, 1994Co-Authors: Manish Soni, R G CooksAbstract:Broad-band excitation of ions is accomplished in the quadrupole ion trap mass spectrometer using notched waveforms created by the SWIFT (stored waveform Inverse Fourier Transform) technique. A series of notched SWIFT pulses are applied during the period of ion injection from an external Cs[sup +] source to resonantly eject all ions whose resonance frequencies fall within the frequency range of the pulse while injecting only those analyte ions whose resonance frequencies fall within the limits of the notch. This allows selective injection and accumulation of the ions of interest and continuous ejection of the unwanted ions. This is shown to result in significant improvement in S/N ratio, resolution, and sensitivity for the analyte ions of interest. Selective ion injection is demonstrated by injecting the protonated molecules of peptides VSV and gramicidin S and the intact cation of l-carnitine hydrochloride, using singly notched SWIFT pulses. Multiply notched SWIFT pulses are used to simultaneously inject ions of different m/z values of l-carnitine hydrochloride into the ion trap. A new coarse/fine ion isolation procedure, which employs a doubly notched SWIFT pulse, is demonstrated for isolating ions of a single m/z value of 4-bromobiphenyl from a population of trapped ions. 36 refs., 10 figs.,more » 2 tabs.« less
Khalil El Khamlichi Drissi - One of the best experts on this subject based on the ideXlab platform.
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wire antenna versus modified transmission line approach to the transient analysis of grounding grid
Engineering Analysis With Boundary Elements, 2011Co-Authors: Damir Cavka, Basma Harrat, Dragan Poljak, Bachir Nekhoul, Kamal Kerroum, Khalil El Khamlichi DrissiAbstract:The paper deals with transient analysis of grounding grids using two different approaches, wire antenna theory and modified transmission line model. The Pocklington integro-differential equations, in frequency domain, arising from the wire antenna theory are numerically handled via the Galerkin–Bubnov variant of indirect Boundary Element Method (GB-IBEM), while the transient response was obtained using Inverse Fourier Transform. The modified transmission line equations are treated using the finite difference time domain (FDTD) method. Some illustrative numerical results are presented and discussed in the paper.
