Sequencing peptides without scanning the reflectron: Post‐source decay with a curved‐field reflectron time‐of‐flight mass spectrometer

A tandem time-of-flight mass spectrometer for the study of photodissociation of biopolymer ions generated by matrix-assisted laser desorption ionization was designed and constructed. A reflectron with linear and quadratic (LPQ) potential components was used. Characteristics of the LPQ reflectron and its utility as the second stage analyzer of the tandem mass spectrometer were investigated. Performance of the instrument was tested by observing photodissociation of [M ϩ H] ϩ from angiotensin II, a prototype polypeptide. Quality of the photodissociation tandem mass spectrum was almost comparable to that of the post-source decay spectrum. Monoisotopic selection of the parent ion was possible, which was achieved through the ion beam-laser beam synchronization. General theoretical considerations needed for a successful photodissociation of large biopolymer ions are also presented. [3] has revolutionized the application of mass spectrometry for the determination of molecular weights of biopolymers. The natural next step in this field is the tandem mass spectrometry, which detects fragmentation of a mass-selected parent ion. When the internal energy of a polyatomic ion acquired at the time of its formation is sufficient for its dissociation after exiting the source, it may dissociate unimolecularly during its flight to the detector, which is called the metastable ion decomposition (MID) [4]. A more popular way to supply additional energy is to introduce collision gas on the ion flight path such that some of parent ion translational energy is converted to its internal energy. This is called the collision-induced dissociation (CID) or collisionally activated dissociation (CAD) [2]. In the case of the tandem time-of-flight (TOF) mass spectrometry of ions generated by MALDI without the collision gas, the term post source decay (PSD) [5,6] rather than MID has been popular because CID may also contribute to the observed fragment ion signals. When tandem mass spectra generated by PSD are either very weak or do not contain sufficient structural information, CID [7][8][9] may be attempted by introducing collision gas intentionally. Excitation via multiple collisions is thought to be important in the CID tandem mass spectrometry of high mass biopolymers with many degrees of freedom. Recently, dissociation of multiply protonated molecules induced by electron capture, or electron capture dissociation (ECD) [10,11], is attracting a lot of attention as a method to obtain site-specific information.Photodissociation (PD) has been utilized in the field of tandem mass spectrometry mostly as a method to study the structure and dissociation dynamics of small polyatomic ions [12]. Infrared multiphoton dissociation (IRMPD) [13,14] has been used to induce dissociation of biopolymer ions also, even though a large amount of internal energy needed for such a dissociation necessitates absorption of a large number of infrared photons. When electronic transitions of chromophores by ultraviolet radiation are utilized, the number of photons that m...

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“…The spectrum is in excellent agreement with that in a previous report [37]. The homemade ion gate had a resolution of 10 ϳ 20 Da.…”

Section: Resultssupporting

confidence: 89%

Tandem time-of-flight mass spectrometer for photodissociation of biopolymer ions generated by matrix-assisted laser desorption ionization (MALDI-TOF-PD-TOF) using a linear-plus-quadratic potential reflectron

Moon

Kim

2004

J. Am. Soc. Mass Spectrom.

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“…Because this type of reflector permits the simultaneous focusing of a wide mass range of fragment ions formed by metastable decay, the product ion mass spectrum can be collected without requiring any stepwise adjustment of the reflectron under unchanged conditions. 9,10 The operating conditions were as follows: nitrogen laser (337 nm); reflectron mode; detection of positive ions. The ion detector of this instrument is an electron multiplier type.…”

Section: Maldi-tof Mass Spectrometrymentioning

confidence: 99%

“…9,10 Thus, the product-ion mass spectra can be collected without an adjustment under the same conditions, thereby eliminating the need to scan the reflector voltage. Therefore, the relative intensity of the PSD fragment ions can be discussed at an accurate level.…”

Section: Introductionmentioning

confidence: 99%

Distinguishing of Linkage Isomers of Lactotetra Oligosaccharides by Using the Relative Ion Intensity Analysis of Post-source Decay Fragment Ions in Curved-field Reflectron Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry

Yamagaki

Nakanishi

2001

ANAL. SCI.

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Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was applied to analyses of biomolecules, such as proteins, peptides and oligosaccharides. [1][2][3][4][5] The post-source decay (PSD) fragmentation of peptides and oligosaccharides occurred at peptide bonds and at glycosyl linkages in MALDI-MS, respectively. Thus, the PSD mass spectra are useful for the sequencing of peptides and saccharides. The sequencing of peptides could be determined by this method because the peptide bond is just one type, and because almost all amino acids have different molecular weights. On the other hand, it is very difficult to determine the fine structure of the saccharide chains by MS because of the existence of many structural isomers with different linkage types. We could obtain and discuss only the simplest sequence information of oligosaccharides, like Hex-HexNAc-Hex-Hex. In the MALDI-PSD fragment mass spectra of some isomers of oligosaccharides, different tendencies in the spectral patterns were observed; 6-8 however, it has been very difficult to quantitatively discuss the ion intensity by using a conventional TOFMS. 8 Unfortunately, it is impossible to compare the ion intensities in the total PSD spectra because these spectra are usually acquired in segments by stepping the reflectron voltage. Sequence information can be extracted from the reconstructed time-of-flight mass spectrum by scanning the voltage of the ion reflector and bringing narrow segments of the product spectrum into focus. Consequently, the signal strength might differ in different segments where the ionization conditions might differ. Although it might be possible to compare the absolute intensities of PSD ions in only a narrow segment, huge accumulations of the actual measurements were required to obtain high reproducibility in the absolute intensity; also, the actual spectra of the huge measurements were hardly measured under the same conditions. A logical and actual solution to this problem would be to use an instrument equipped with a reflectron, which records all fragment ions in a single spectrum.A new type of reflector of curved-field reflectron in a TOF mass detector enables the simultaneous focusing of a wide mass range of metastable fragment ions and the observation of the entire PSD fragment spectrum in a single experiment. 9,10 Thus, the product-ion mass spectra can be collected without an adjustment under the same conditions, thereby eliminating the need to scan the reflector voltage. Therefore, the relative intensity of the PSD fragment ions can be discussed at an accurate level. In this work, we studied a new method of a structure analysis for the glycosylation and/or glycoconjugates using the ion intensities of the PSD fragment ions in the curvedfield reflectron MALDI-TOF mass spectra.Previously, we studied the PSD fragment spectra of sugarbranched cyclodextrin derivatives by using curved-field reflectron MALDI-TOFMS. [11][12][13][14][15] The PSD ions produced from the branch had higher intensities than...

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“…Further, tandem time-of-flight mass spectrometry (TOF/TOF) is a technique in which two time-of-flight mass spectrometers are arranged in tandem and used consecutively [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Precursor ions are selected by the first time-of-flight mass spectrometer (TOF1), and the fragment ions derived from them are mass analyzed by the second time-of-flight mass spectrometer (TOF2).…”

Section: Introductionmentioning

confidence: 99%

“…With the exception of tandem sector mass spectrometry, MALDI-TOF/TOF is the only instrument capable of observing HE-CID fragment pathways [17]. On the other hand, the ions generated by MALDI often cause post-source decay (PSD) [11][12][13][14]. The overlapping of PSD and HE-CID fragment pathways complicates the product ion spectrum.…”

Section: Introductionmentioning

confidence: 99%

Tandem Time-of-Flight Mass Spectrometer with High Precursor Ion Selectivity Employing Spiral Ion Trajectory and Improved Offset Parabolic Reflectron

Satoh

Sato

Kubo

et al. 2011

J. Am. Soc. Mass Spectrom.

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In this study, we have developed a tandem time-of-flight mass spectrometry (TOF/TOF) technique involving the use of a matrix-assisted laser desorption/ionization ion source that exhibits high precursor ion selectivity. An ion optical system with a 17 m spiral ion trajectory was used in the first time-of-flight mass spectrometer. High precursor ion selectivity was achieved by realizing a 15 m flight path, which is considerably longer than that of the conventional MALDI-TOF/TOF before the precursor ion selection by an ion gate; monoisotopic ions could be selected properly up to m/z 2500. Furthermore, the first time-of-flight mass spectrometer was composed of electrostatic sectors and could eliminate post-source decay (PSD) ions. Precursor ions with 20 keV kinetic energy were selected and injected into a collision cell, leading to the generation of fragment ions by high-energy collision-induced dissociation (HE-CID). The optimized second time-of-flight mass spectrometer included a post-acceleration region and an offset parabolic reflectron to record product ion spectra in the entire mass range. Our system could generate a simple HE-CID product ion spectrum because each fragment pathway could be observed as a single peak by the selection of monoisotopic ions of all precursor ions and HE-CID fragment pathways could be predominantly observed by the PSD ion elimination.

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Sequencing peptides without scanning the reflectron: Post‐source decay with a curved‐field reflectron time‐of‐flight mass spectrometer

Cited by 54 publications

References 10 publications

Tandem time-of-flight mass spectrometer for photodissociation of biopolymer ions generated by matrix-assisted laser desorption ionization (MALDI-TOF-PD-TOF) using a linear-plus-quadratic potential reflectron

Tandem time-of-flight mass spectrometer for photodissociation of biopolymer ions generated by matrix-assisted laser desorption ionization (MALDI-TOF-PD-TOF) using a linear-plus-quadratic potential reflectron

Distinguishing of Linkage Isomers of Lactotetra Oligosaccharides by Using the Relative Ion Intensity Analysis of Post-source Decay Fragment Ions in Curved-field Reflectron Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometry

Tandem Time-of-Flight Mass Spectrometer with High Precursor Ion Selectivity Employing Spiral Ion Trajectory and Improved Offset Parabolic Reflectron

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