Stored Waveform Inverse Fourier Transform Research Articles

SWIFTSIN: A High-Resolution Ion Isolation Waveform for the Miniaturized Linear Ion Trap Mass Spectrometer by Coarse to Fine Excitation

To figure out the reason for the drawback of the stored waveform inverse Fourier transform (SWIFT) waveform and realize the high-resolution ion isolation on the miniaturized linear ion trap mass spectrometer, we studied the efficiency that ions can be excited under different excitation durations and amplitudes at different frequencies and compared the overlap ratios of the effective excitation frequency bandwidths of the adjacent ions. According to this, we proposed a new coarse-to-fine isolation waveform named SWIFTSIN. By superposing one or more sinusoidal waveforms on the SWIFT waveform and modulating the phases of the superposed sinusoidal waveforms, the generated SWIFTSIN waveform can achieve unit mass isolation on the miniaturized linear ion trap mass spectrometer without reducing the intensity of the target ion. The isolation ability of the SWIFTSIN waveform was verified by isolating a single isotope peak in the mixed samples.

Enhancement of Portable Mass Spectrometer Sensitivity and Selectivity by a Qualitative Pre-Scan Waveform (QPSW)

While portability is a key aspect of small mass spectrometers, they also need to be able to effectively screen the analytes from complex matrices. The accuracy and performance of mass spectrometers depend not only on the identification of parent ion signals in targets but also fragment ion signals. This paper reports on the construction of a device that uses a new time-domain excitation waveform called qualitative pre-scan waveform (QPSW) for its quadrupole ion trap mass spectrometry analyzer. This approach uses scanning to eliminate interfering ions, thus improving the sensitivity for the analyte and removing the cumbersome steps required to convert conventional stored waveform inverse Fourier transform (SWIFT) waveforms from the frequency domain to the time domain. Tests show that the target ions can be fragmented just by introducing air at the moment when the pinch valve is opened without any need for a carrier gas. This simplifies the equipment required, making the mass spectrometer more portable. Tests were undertaken to compare the performance with the use of conventional SWIFT waveforms and to optimize its experimental parameters so that the target ions were effectively accumulated in the ion trap. An approximate 5-fold improvement in sensitivity was achieved by QPSW compared to the SWIFT for 2 μg/mL ketamine. A 5-fold reduction in the limit of detection (LOD) to 20 ng/mL was also obtained for enrofloxacin. In addition, the stability was improved by QPSW with a relative standard deviation less than 13% compared to 16% for SWIFT.

Ultrahigh Resolution Ion Isolation by Stored Waveform Inverse Fourier Transform 21 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Stored waveform inverse Fourier transform (SWIFT) is a versatile method to generate complex isolation/ejection waveforms for precursor isolation prior to tandem mass spectrometry experiments. Here, we report ultrahigh resolving power ion isolation by SWIFT on a 21 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Individual histone proteoforms are isolated (0.6 m/z isolation window) with near 100% efficiency using a 52 ms SWIFT isolation, followed by in-cell fragmentation by ultraviolet photodissociation (UVPD). Ion isolation resolving power of 175 000 (m/Δm) is demonstrated by isolation of individual peaks at a spacing of 0.0034 Da at m/z 597 from a complex mixture of Canadian bitumen. An individual m/z ion, which corresponds to a single elemental composition, from a complex mixture is isolated and fragmented by infrared multiphoton dissociation (IRMPD). Theoretical and experimental considerations that limit achievable ion isolation resolving power are discussed.

Operation and Performance of a Mass-Selective Cryogenic Linear Ion Trap.

We report on the performance of a cryogenic 2D linear ion trap (cryoLIT) that is shown to be mass-selective in the temperature range of 17-295K. As the cryoLIT is cooled, the ejection voltages during the mass instability scan decrease, which results in an effective mass shift to lower m/z relative to room temperature. This is attributed to a decrease in trap radius caused by thermal contraction. Additionally, the cryoLIT generates reproducible mass spectra from day-to-day, and is capable of performing stored waveform inverse Fourier transform (SWIFT) mass isolation of fragile N2-tagged ions for the purpose of background-free infrared dissociation spectroscopy. Graphical Abstract ᅟ.

Mars Organic Molecule Analyzer (MOMA) laser desorption/ionization source design and performance characterization

The Mars Organic Molecule Analyzer (MOMA), a dual-source, ion trap-based instrument capable of both pyrolysis-gas chromatography mass spectrometry (pyr/GC–MS) and laser desorption/ionization mass spectrometry (LDI-MS), is the core astrobiology investigation on the ExoMars rover. The MOMA instrument will be the first spaceflight mass analyzer to exploit the LDI technique to detect refractory organic compounds and characterize host mineralogy; this mode of analysis will be conducted at Mars ambient conditions. In order to achieve high performance in the Martian environment while keeping the instrument compact and low power, a number of innovative designs and components have been implemented for MOMA. These include a miniaturized linear ion trap (LIT), a fast actuating aperture valve with ion inlet tube, and a Microelectromechanical System (MEMS) Pirani sensor. Advanced analytical capabilities like Stored Waveform Inverse Fourier Transform (SWIFT) for selected ion ejection and tandem mass spectrometry (MS/MS) are realized in LDI-MS mode, and enable the isolation and enhancement of specific mass ranges and structural analysis, respectively. We report here the technical details of these instrument components as well as system-level analytical capabilities, and we review the applications of this technology to Mars and other high-priority targets of planetary exploration.

Isobaric beam purification for high precision Penning trap mass spectrometry of radioactive isotope beams with SWIFT

The Stored Waveform Inverse Fourier Transform (SWIFT) technique offers general and versatile broadband, mass-selective excitation schemes. The method has hitherto been unharnessed for high precision Penning trap mass spectrometry, in which the atomic mass is determined, and is of particular importance at radioactive isotope beam facilities. Herein, we present the first implementation of SWIFT to clean isobaric contaminants at such a spectrometer. The isobaric separation of CO+ and N2+ as well as a high-accuracy mass measurement with SWIFT cleaning were demonstrated at the Low Energy Beam and Ion Trap (LEBIT) facility; resolving powers of 4 × 104 (Δν=300Hz) and 2 × 105 (Δν=60Hz) were achieved for 23Na+ for cleaning times of 20 and 100ms respectively. These measurements demonstrate the viability of SWIFT for fast, efficient, and universal beam purification at high-precision Penning trap mass spectrometers.

A method for isolating ions in quadrupole ion traps using an excitation waveform generated by frequency modulation and mixing

We describe a new method for isolating ions in quadrupole ion traps using an excitation waveform generated by mixing a broadband waveform generated by frequency modulation (FM) with a sine-wave at the secular frequency of the ion to be isolated. In terms of resolution and efficiency, the mixed FM method exhibits performance nearly identical to isolation using the apex of the Mathieu stability diagram. A disadvantage of the mixed FM method is that isolations require additional time relative to apex-based methods. This disadvantage is shared by other methods that involve application of multi-frequency waveforms such as stored waveform inverse Fourier transform (SWIFT). An advantage of the mixed FM technique (also shared with other tailored waveform approaches), is applicability to a much larger m/z range than apex-based methods. Indeed, the mixed FM technique performs identically to SWIFT in many respects. While the mixed FM technique is not nearly as flexible as SWIFT in terms of the frequency content of the generated waveforms, the mixed FM technique is much simpler to implement as it requires only two function generators and a frequency mixer. Tuning important parameters of the waveform such as notch frequency, notch width, and excitation bandwidth is also facilitated with the mixed FM technique.

Elemental Composition Validation from Stored Waveform Inverse Fourier Transform (SWIFT) Isolation FT-ICR MS Isotopic Fine Structure

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 (15)N and (18)O 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.

Analytical Performance of Printed Circuit Board Ion Trap Array Mass Analyzer with Electrospray Ionization

The analytical performance of rectilinear ion trap array made up of printed circuit board material has been determined.The experimental results indicate that the intensity of ions determined was affected dramatically by ion kinetic energy,as in 18 eV,the arginine(Arg) ion(m/z 175.2) dominated in the mass spectrum.The ion trap array can perform multiple sample ion storage,mass-selected ion isolation,ion ejection and collision induce dissociation.The ions of m/z 175.2,117.3 and 71.8 were isolated by stored wave form inverse Fourier transform(SWIFT) notch 50-60 kHz,75-85 kHz,130-145 kHz,respectively.The ions of m/z 175.2,117.3 and 71.8 were ejected selectively using 55 kHz,80 kHz and 135 kHz sine wave.In helium gas,the fragment ions of m/z 157.2,130.3 and 117.3 were obtained by the fragmentaion reaction of Arg precursor ion(m/z 175.2) using 102 kHz sine wave.The ion detection efficiency was determined by electric current integration method,which indicated that the ion detection efficiency was estimated to be 46.3% in 256 kHz AC resonance ejection and was about 9.7% in boundary ejection.

Fourier Transform Mass Spectrometry

This article provides an introduction to Fourier transform-based mass spectrometry. The key performance characteristics of Fourier transform-based mass spectrometry, mass accuracy and resolution, are presented in the view of how they impact the interpretation of measurements in proteomic applications. The theory and principles of operation of two types of mass analyzer, Fourier transform ion cyclotron resonance and Orbitrap, are described. Major benefits as well as limitations of Fourier transform-based mass spectrometry technology are discussed in the context of practical sample analysis, and illustrated with examples included as figures in this text and in the accompanying slide set. Comparisons highlighting the performance differences between the two mass analyzers are made where deemed useful in assisting the user with choosing the most appropriate technology for an application. Recent developments of these high-performing mass spectrometers are mentioned to provide a future outlook.

Technical developments for an upgrade of the LEBIT Penning trap mass spectrometry facility for rare isotopes

The LEBIT (Low Energy Beam and Ion Trap) facility is the only Penning trap mass spectrometry (PTMS) facility to utilize rare isotopes produced via fast-beam fragmentation. This technique allows access to practically all elements lighter than uranium, and in particular enables the production of isotopes that are not available or that are difficult to obtain at isotope separation on-line facilities. The preparation of the high-energy rare-isotope beam produced by projectile fragmentation for low-energy PTMS experiments is achieved by gas stopping to slow down and thermalize the fast-beam ions, along with an rf quadrupole cooler and buncher and rf quadrupole ion guides to deliver the beam to the Penning trap. During its first phase of operation LEBIT has been very successful, and new developments are now underway to access rare isotopes even farther from stability, which requires dealing with extremely short lifetimes and low production rates. These developments aim at increasing delivery efficiency, minimizing delivery and measurement time, and maximizing use of available beam time. They include an upgrade to the gas-stopping station, active magnetic field monitoring and stabilization by employing a miniature Penning trap as a magnetometer, the use of stored waveform inverse Fourier transform (SWIFT) to most effectively remove unwanted ions, and charge breeding.

High Mass Selectivity for Top-Down Proteomics by Application of SWIFT Technology

Stored waveform inverse Fourier transform (SWIFT) technology has been implemented on a commercial Fourier transform ICR mass spectrometer. Complex ejection/isolation waveforms can be generated on an arbitrary waveform generator (AWG) and applied to the instrument by use of a high speed analog switch. High mass selectivity and subsequent electron capture dissociation (ECD) of the SWIFT isolated ions has been demonstrated with analysis of intact Bovine histone H4. A mass selectivity about 0.1 m/z unit for isolation of the 18+ charge state ions was achieved. Adaptation of SWIFT on the commercial instrument provides an enhanced capability for characterizing intact proteins by top-down analysis.

Improved Mass Accuracy for Higher Mass Peptides by Using SWIFT Excitation for MALDI-FTICR Mass Spectrometry

Stepwise-external calibration has previously been shown to produce sub part-per-million (ppm) mass accuracy for the MALDI-FTICR/MS analyses of peptides up to m/z 2500. The present work extends these results to ions up to m/z 4000. Mass measurement errors for ions of higher mass-to-charge are larger than for ions below m/z 2500 when using conventional chirp excitation to detect ions. Mass accuracy obtained by using stored waveform inverse Fourier transform (SWIFT) excitation was evaluated and compared with chirp excitation. Analysis of measurement errors reveals that SWIFT excitation provides smaller deviations from the calibration equation and better mass accuracy than chirp excitation for a wide mass range and for widely varying ion populations.

Studies into the selective accumulation of multiply charged protein ions in a quadrupole ion trap mass spectrometer

In seeking to improve the limit of detection of an electrospray ionization/quadrupole ion trap mass spectrometer (ESI/ITMS) for the analysis of multiply charged protein ions, studies related to the selective accumulation of these ions during ion injection have been undertaken. This was achieved by the interfacing of an Odyssey data system and the associated electronics used for arbitrary waveform generation from a Fourier transform mass spectrometer (FTMS) (ThermoFinnigan, Bremen, Germany) to an LCQ™ ‘classic’ quadrupole ion trap mass spectrometer (ThermoFinnigan, San Jose, CA). This allows the application of user defined stored waveform inverse Fourier transform (SWIFT) waveforms. These studies examined the efficiency of ejection and isolation at different q z values for a particular charge state from the distribution of ions usually observed with the electrospray ionization of proteins, and the variation in the intensity of a particular ion as a function of the accumulation time. In addition, this selective accumulation technique allowed for an order of magnitude improvement in the detection limit of this instrument, with the resulting reduction in space charge producing a five-fold increase in spectral resolution (FWHM) under the conditions studied.

Tool command language automation of the modular ion cyclotron data acquisition system (MIDAS) for data-dependent tandem Fourier transform ion cyclotron resonance mass spectrometry.

This manuscript describes the addition of data-dependent automation to the modular ion cyclotron resonance data acquisition system (MIDAS). The automation is made possible by developments and incorporation of a tool command language (Tcl) interpreter for automated acquisition. To accomplish the automation, real-time generation of excitation waveforms and scriptable data post-processing has been implemented into the MIDAS source code. In addition a new excitation event has also been added to allow for run-time generation of a single notch stored waveform inverse Fourier transform (SWIFT) excitation event. Examples of these new features and discussion of their enhancement to the existing data station are presented.

Mass spectrometric investigation of N-sulfonylated purine nucleic bases and nucleosides.

The gas/phase behaviour of N-sulfonylated purine nucleic bases and nucleosides towards electron impact (EI) and matrix-assisted laser desorption/ionization (MALDI) occurring in a ion trap of a Fourier transform ion cyclotron resonance mass spectrometer is investigated. The influence of the storage time on the protonated molecule ([M+H](+)) abundance under EI conditions confirms that the formation of these ions proceeds through ion/molecule reactions. Using stored-waveform inverse Fourier transform (SWIFT) selective isolation of M(+.) or H(3)O(+), self-chemical ionization, M(+.)/M, and chemical ionization, H(3)O(+)/M, are detected. Investigation of specific EI expulsion of SO(2), SO(2)H and/or SO(2)H(2) from M(+.) and/or [M+H](+) shows that oxygen protonation in bond;SO(2)bond; proceeds faster than nitrogen protonation. Expulsion of SO(2) from molecular ions is not observed in MALDI mass spectra of nucleosides.

On-line capillary electrophoresis/microelectrospray ionization-tandem mass spectrometry using an ion trap storage/time-of-flight mass spectrometer with SWIFT technology.

The development of a system capable of the speed required for on-line capillary electrophoresis-tandem mass spectrometry (CE-MS/MS) of tryptic digests is described. The ion trap storage/reflectron time-of-flight (IT/reTOF) mass spectrometer is used as a nonscanning detector for rapid CE separation, where the peptides are ionized on-line using electrospray ionization (ESI). The ESI produced ions are stored in the ion trap and dc pulse injected into the reTOF-MS at a rate sufficient to maintain the separation achieved by CE. Using methodology generated by software and hardware developed in our lab, we can produce SWIFT (Stored Waveform Inverse Fourier Transform) ion isolation and TICKLE activation/fragmentation voltage waveforms to generate MS/MS at a rate as high as 10 Hz so that the MS/MS spectra can be optimized on even a 1-2 s eluting peak. In CE separations performed on tryptic digests of dogfish myelin basic protein (MBP) where eluting peaks 4-8 s wide are observed, it is demonstrated that an acquisition rate of 4 Hz provides > 20 spectra/peak and is more than sufficient to provide optimized MS/MS spectra of each of the eluting peaks in the electropherogram. The detailed structural analysis of dogfish MBP including several posttranslational modifications using CE-MS and CE-MS/MS is demonstrated using this method with < 10 fmol of material consumed.

High-field fourier transform ion cyclotron resonance mass spectrometry for simultaneous trapping and gas-phase hydrogen/deuterium exchange of peptide ions

Gas-phase hydrogen/deuterium exchange of D 2O with [M + H] + ions of angiotensin II, angiotensin I, [Sar 1]-angiotensin II, bradykinin, des-Arg 1-bradykinin, des-Arg 9-bradykinin, luteinizing hormone releasing hormone (LH-RH), and substance P has been examined by Fourier transform ion cyclotron resonance mass spectrometry at 9.4 tesla. Because the FTICR dynamic range increases quadratically with magnetic field, parent ions from a mixture of several peptides may be confined simultaneously for long periods at high pressure (e.g., 1 h at 1 × 10 −5 torr) without quadrupolar axialization (and its attendant ion heating), for faster data acquisition and better controlled comparisons between different peptides. A high magnetic field also facilitates stored waveform inverse Fourier transform (SWIFT) isolation of monoisotopic [M + H] + parent ions, so that deuterium incorporation patterns may be determined directly without the need for isotopic distribution deconvolution. Finally, a higher magnetic field provides for a greatly extending trapping period, for measurement of much slower rates. Angiotensin I, angiotensin II, and [Sar 1]-angiotensin II are found to undergo a rapid exchange. Angiotensin II and [Sar 1]-angiotensin II exhibit multiple deuterium uptake distributions, corresponding to multiple gas-phase conformations. In contrast, substance P exchanges slowly and LH-RH displays no observable exchange. Comparison of the relative H/D exchange rates for bradykinin and its des-Arg-derivatives supports the hypothesis that bradykinin adopts a folded gas-phase conformation that unfolds upon removal of either terminal arginine residue.

Stored waveform inverse Fourier transform (SWIFT) ion excitation in trapped-ion mass spectometry: Theory and applications

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.

High-resolution multistage MS, MS2, and MS3 matrix-assisted laser desorption/ionization FT-ICR mass spectra of peptides from a single laser shot.

By combined and repeated use of sustained off-resonance irradiation (SORI) for ion dissociation, stored waveform inverse Fourier transform (SWIFT) waveforms for ion isolation, and ion axialization and remeasurements techniques, we obtain for the first time MS, MS2, and MS3 FT-ICR mass spectra from peptide ions (enzymatic digest products of horse cytochrome c) produced from a single laser shot. The successive fragmentation of gas-phase ions detected from the same initial batch of ions increases the sensitivity of analysis of trace amounts of biological samples in structural mass spectrometry, and fragment identification is facilitated by resolution of carbon-13 isotopic distributions. The method is illustrated by analyses of subfemtomole amounts of crudely purified samples of tryptic digest solutions of horse cytochrome c and bovine cytochrome c. The high-resolution primary ion mass spectrum, along with the collision-induced dissociation (CID) and MSn capabilities of FT-ICR, help to determine the primary amino acid sequence of the fragment ions beyond what is obtained from enzymatic digestion alone, without prior chromatographic separation and purification.