Reflectron, mass analyzer

ToF measurements can be performed using a linear or reflectron mass analyzer. The former comprises a basic ToF layout, whereas the latter uses an ion mirror to time-focus the ions onto the detector. The linear detector is used for intact protein analysis owing to its ability to detect a very wide mass range, up to 100,000 Da (26). The reflectron geometry offers higher mass resolution capabilities, but has a more limited mass range, typically below 5000 Da. 

An algorithm that capitalizes on the correlation between the positions and velocities of desorbed ions has been developed to increase the mass resolution of linear TOP instruments. ° It is applicable to low- and high-mass ions and may also improve the performance of reflectron mass analyzers. 

Figure 6 Schematic drawing of a MALDI-TOF instrument that is equipped with a reflectron mass analyzer. The extraction grids allow one to diminish the initial width of the ion cloud by delayed extraction (DE) and thus to achieve higher mass resolution (see also Fig. 10 for fragment ion analysis in a reflectron). (From Ref. 19.)...

Schematic diagram of a time-of-flight reflectron mass analyzer.

TOF/RTOF Linear mass analyzer with an orthogonal reflectron mass analyzer Schey et aL ... 

We use laser photofragment spectroscopy to study the vibrational and electronic spectroscopy of ions. Our photofragment spectrometer is shown schematically in Eig. 2. Ions are formed by laser ablation of a metal rod, followed by ion molecule reactions, cool in a supersonic expansion and are accelerated into a dual TOE mass spectrometer. When they reach the reflectron, the mass-selected ions of interest are irradiated using one or more lasers operating in the infrared (IR), visible, or UV. Ions that absorb light can photodissociate, producing fragment ions that are mass analyzed and detected. Each of these steps will be discussed in more detail below, with particular emphasis on the ions of interest. 

Both collisional activation (in ion traps) and post source decay (in curved field reflectron TOF analyzers) have been used successfully to obtain sequence ions from peptides prepared in situ on the sample holder. Single Dalton mass windows are advantageous for precursor selection, as are realized in ion-trap and trap-TOF configurations. Publicly available search algorithms can be used... 

Fig. 11.13. Diagram of a TOF mass analyzer (with reflectron). Ions enter from an external source and are accelerated (orthogonally) by the pusher electrode toward the reflectron. The reflectron (ion mirror) retards, reverses and reaccelerates the ions back toward the micro-channel plate detector.

Figure 3.11 Schematic of a time-of-flight mass analyzer with reflectron proposed by Mamyrin,11 Ions of higher kinetic energy penetrate more deeply into the reflecting field and are delayed in comparison to ions of lower kinetic energy. The delay compensates for differences in transit time of the field-free regions. Ions produced e.g., by focused laser or primary ion beam.

TOFSIMS analyses were performed on a Kratos PRISM instrument. It was equipped with a reflectron-type time-of-flight mass analyzer and a pulsed 25 kV liquid metal ion source of monoisotopic 69Ga ions with a minimum beam size of 500 A. Positive and negative spectra were obtained at a primary energy of 25 keV, a pulse width of 10-50 ns, and a total integrated ion dose of about 10" ions/cm2. This is well below the generally accepted upper limit of 5 x 1012 ions/cm2 for static SIMS conditions in the analysis of organic materials [12], The mass resolution at mass 50 amu varied from M/AM= 1000 at 50 ns pulse width to about 2500 at 10 ns pulse width. 

Mass analyzer/ Feature Linear Quadrupole Quadrupole ion trap Linear time-of-flight Reflectron time-of-flight... 

Ions produced by SPI are detected and mass analyzed by a reflectron TOF mass spectrometer having a resolution of m/Am = 1000. The sample is introduced into the... 

The electric field E of the reflectron (energy 1 to 25 kV) acts as a second mass analyzer. 

There are several types of ionization sources [MALDI, ESI, FAB (fast atom bombardment), PD (Cf-252 plasma desorption), El (electron ionization), Cl (chemical ionization) etc.], different types of mass analyzers [combinations of magnetic and electric sectors, quadrupolar filters (Q) and ion traps (IT), time-of-flight (TOF) and FT-ICR] and different detectors, each with its own advantages and drawbacks. We describe herein only the systems that presently have widespread use for the study of biomolecules ESI coupled to a quadrupole (or triple quadrupole, QqQ) mass analyzer or an ion trap, the MALDI source with the linear or reflectron TOF analyzer, and the FT-ICR system which can be equipped with both ESI and MALDI sources. 

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