Reflectron time of flight mass

Figure 6.15 Schematic design of a reflectron time-of-flight mass spectrometer...

Chien, B. M. Michael, S. M. Fubman, D. M. Enhancement of resolution in matrix-assisted laser desorption using an ion-trap storage/reflectron time-of-flight mass spectrometer. Rapid Comm. Mass Spectrom. 1993, 7,837-843. 

B.A. Mamyrin, Laser assisted reflectron time-of-flight mass spectrometry, hit. J. Mass Spectrom. Ion Proc., 131 (1994) 1-19. 

Reflectron time-of-flight mass spectrometers can be used to generate fragment spectra. Before the introduction of delayed extraction, it was observed that the ions had a tendency to disassemble into fragments while they were traveling to the reflectron (Spengler et al., 1992). This behavior is called postsource decay (PSD). The ions collide with matrix ions in the gas phase when they are accelerated with several kilovolts. Their decay occurs in the first field-free drift region. 

Wu, J. T., Huang, P. Q., Li, M. X., Qian, M. G., and Lubman, D. M. (1997). Open-tubular capillary electrochromatography with an on-line ion trap storage/reflectron time-of-flight mass detector for ultrafast peptide mixture analysis. Anal. Chem. 69, 320-326. 

A technique specific to reflectron time-of-flight mass spectrometers where product ions of metastable transitions or collision-induced dissociations generated in the drift tube prior to entering the reflectron are m/z separated to yield product ion spectra... 

Li, M. X. Wu, J. T. Parus, S. Lubman, D. M. 1998. Development of a three-dimensional topographic map display for capillary electrophoresis/mass spectrometry with an ion trap/reflectron time-of-flight mass spectrometer detector applications to tryptic digests of isoforms of myelin basic protein. ./. Am. Soc. Mass Spectrom., 9,701-709. 

Kaufmann R, Chaurand P, Kirsch D, Spengler B. Post-source decay and delayed extraction in matrix-assisted laser desorption/ionization-reflectron time-of-flight mass spectrometry. Are there trade-offs . Rapid Commun Mass Spectrom 1996 10 1199-1208. 

Until now, most studies of dissociation dynamics of metastable cluster ions have been made using a double-focusing mass spectrometry method (Lifshitz et al. 1990 Lifshitz and Louage 1989, 1990 Stace 1986). As discussed herein, the novel technique of reflectron time-of-flight mass spectrometry is a valuable alternative approach to more standard methods. With carefully designed experiments, it is possible to derive both kinetic energy releases and decay fractions for... 

A TOF mass analyser requires a pulsed ion introduction. In an electrospray-TOF combination, the duty cycle is an important issue. A significant improvement in the duty cycle can be achieved in an ion-trap-TOF hybrid instmment the ions from a continuous ion source are accumulated in the ion trap between two ion introduction events. An ion-trap-TOF hybrid instrument was first described by the group of Lubman [68-69]. The system consists of an atmospheric-pressure ion source with a vacuum interface, a set of Einzel lenses, an ion-trap device, and a reflectron time-of-flight mass analyser. The system was applied for fast analysis in combination with a variety of separation techniques [70]. 

Due to the pulsed nature of most of these experiments, much of the work to date has been performed using time-of-flight mass spectrometers. Quadrupole mass spectrometers are also well suited, especially with higher duty cycle systems. Design of the instruments has followed conventional approaches, for which the resolution limits the size and complexity of the cluster and cluster-adduct species that can studied. One serious problem is the isotopic abundance of many of the metals, which serves to complicate mass spectra. Isotopi-cally pure materials, such as used in measurements of hydrogen uptake on Fe clusters, " simplify the mass spectra. Use of the reflectron time-of-flight mass spectrometer allows the study of metastable clusters and cluster adducts. Details of different instrument designs are described in the references. 

Kaufmann, R., Spengler, B., and Lutzenkirchen, F. (1993). Mass spectrometric sequencing of linear peptides by product-ion analysis in a reflectron time-of-flight mass spectrometer using matrix-assisted laser desorption ionisation, Rapid Commun. Mass Spectrom., 7,902. 

JT Wu, MG Qian, MX Li, K Zheng, DH Huang, DM Lubman. On-line analysis by capillary separations interfaced to an ion trap storage/reflectron time-of-flight mass spectrometer. J Chromatogr A 794 377, 1998. 

Figure 9.8 Schematic of a reflectron time of flight mass analyser. Reflectron lenses act as an electrostatic mirror to both increase the effective length of the flight path, but also to compensate for ion kinetic energy variations (Uq), resulting in higher mass accuracy relative to purely linear time of flight mass analyzers. Consequently, linear time of flight analyzers are nowadays largely obsolete.

Li M X, Liu L, Wu J T, et al. (1997). Use of a polybrene capillary coating in capillary electrophoresis for rapid analysis of hemoglobin variants with on-line detection via an ion trap storage/reflectron time-of-flight mass spectrometer. Analyt. Chem. 69 2451-2456. 

Huang, P., Wu, J.T., and Lubman, D.M., Separation of tryptic digests using a modified buffer in pressurized capillary electrochromatography with an ion trap storage/reflectron time-of-flight mass spectrometer, AnoZ. Chem., 70, 3003, 1998. 

The precursor ion selection, fragmentation, and product ion analysis can be separated in space or in time, as shown in Figure 1.29. Separation in time requires trapped ions, as available in the quadrupole ion trap or the ion cyclotron resonance trap. Separation in space necessitates at least two physically distinct mass analyzing devices, one for precursor ion selection (MS-1) and one for product ion analysis (MS-2). The simplest in-space tandem instruments are the triple quadrupole mass spectrometer (QqQ), the double-focusing sector tandem mass spectrometer (EB or BE), and the reflectron time-of-flight mass spectrometer. In a triple quadrupole, the first and third quadrupoles (Q) are mass analyzers, while the center quadrupole iq) serves as the collision cell. In sector instruments, a collision cell is situated... 

Mamyrin, B. A., Laser Assisted Reflectron Time-of-Flight Mass Spectrometry, Ini.. Mass Specirom. Ion Proc., 1, 131, 1994. 

Kaufmann, R., Chaurand, R, Kirsch, D., and Spengler, B., Post-source Decay and Delayed Extraction in Matrix-assisted Laser Desorption/Ionization-Reflectron Time-of-Flight Mass Spectrometry. Are There Trade-offs , Rapid Comm. Mass. Spectrom., 10, 1199, 1996. 

UNIMOLECULAR ION DECAY IN A REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETER... 

Benzene ions are produced in an effusive molecular beam inside the acceleration field of a reflectron time-of-flight mass spectrometer /12/. (see Fig. 3). Laser 1 is tuned to the frequency of the 6 i or 60116 -1 band and produces, via a resonance-enhanced two photon absorption, state- and energy-selected benzene cations. 

Figure 3 Scheme of a two laser pump-pump experiment for the production of internal energy-selected molecular ions in a reflectron time-of-flight mass spectrometer (from ref. /15/). Laser 1 produces state-selected molecular ions and 200 ns later laser 2 excites these ions to a well defined internal energy level above dissociation threshold. The dissociation rate constants of the energy-selected ions are measured by the technique of detection and energy analysis of metastable ions. 

In conclusion, we have shown that resonantly enhanced two-photon ionization is a versatile method for the production of state- and energy-selected polyatomic molecular ions. This was explicitly demonstrated by an analysis of the kinetic energy distribution of the ejected photoelectrons. In a reflectron time-of-flight mass spectrometer the total decay rate constants and individual decay rate constants of internal energy-selected molecular ions have been measured for various well defined internal energies. From our experimental results detailed information about the statistical character of the dissociation mechanism and the structure of the activated complex is obtained. 

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