Linear-TOF

For a simple linear TOF analyzer of length d, the arrival time at the detector is... 

Figure 6.3 Differentiation of Vibrio parahaemolyticiis strains by region of clinical outbreak, showing the correlation of a mass spectral feature (near dotted line), the region of clinical outbreak, and the presence or absence of the TDH gene in control organisms. (From a linear TOF, reported at the American Society for Mass Spectrometry in...

For comparison purposes, two other MS systems have been used with in vitro grown parasite cultures. In the first case, a home-built miniaturized linear TOF multi-array analyzer1718 was interfaced to the frequency-tripled output at 355nm of a Q-switched Nd-YAG laser ( Polaris, New Wave Research, Fremont, CA). In this experiment the laser beam was not scanned, and the estimated laser fluence after attenuation was similar to that of the commer-... 

Fig. 4.4. Scheme of a linear TOF instrument. After being created during a laser pulse onto the sample layer, ions are continuously accelerated by a voltage U. While drifting along the field-free drift path s, they are dispersed in time. Lighter ions reach the detector first. 

Prieto, M.C. Kovtoun, V.V. Cotter, R.J. Miniaturized Linear TOF Mass Spec-... 

Another type of dynamic mass spectrometer is the time-of-flight (ToF) analyzer. In 1946, Stephens presented his concept of the linear time-of-flight mass spectrometer (ToF-MS) as the simplest mass separation technique at an American Physical Society meeting in Cambridge, MA.49 Cameron and Eggers first published the design and showed mass spectra for linear ToF-MS in... 

The principle underlying time of flight (TOF) mass spectrometers is based on the relationship that exists between mass and velocity at a given kinetic energy. The instrument, which uses pulsed ionisation, measures the time taken by each mass to travel the length L of a field-free analyser tube. The basic equation (I6.l l) used in linear TOF analysers is obtained by eliminating the velocity v from equation (16.5) in conjunction with the relationship L = vt ... 

Figure 2. Schematic view of the experimental setup. The femtosecond laser beam is crossed with a cold sodium molecular beam. A linear TOF spectrometer is used for mass-and energy-resolved ion and electron detection.

In a simple linear TOF instrument (Fig. 20), ions are formed within the source region(s) in the presence of an electrical field (V). The field accelerates the ions into a field-free region (d), which the ions all ideally enter with the same kinetic energy (KE) defined by the accelerating potential. Subsequently as the ions drift... 

These distributions are the major origins of the poor resolution observed using simple linear TOF instrumentation. Resolution (R) for a TOF mass spectrometer is dependent on peak width (At) and the total flight time (t) ... 

Dong H, Kemptner J, Marchetti-Deschmann M, Kubicek C, Allmaier G (2009) Development of a MALDI two-layer volume sample preparation technique for analysis of colored conidia spores of Fusarium by MALDI linear TOF mass spectrometry. Anal Bioanal Chem 395 1373-1383. doi 10.1007/s00216-009-3067-3... 

The major deficiency of a simple linear TOF instrument is its insufficient mass resolution, resulting from flight time variations of ions of the same m/e ratio. The ionization process adds a certain amount of initial kinetic energy to the molecules before acceleration. In addition, the different spatial positions in the source from where the ions are formed lead to varying values of l, and thus to flight time variations. As a result, modern TOF instruments commonly employ a technique called reflection to enhance resolution. A reflectron TOF (RETOF) [4] (Fig. 3) is used to focus ions of the same... 

The QitTof mass spectrometer has MS" capability. Its mass resolution, m/Am, for mass 181 amu, ranges from 100-200 for a 22-cm flight-path linear TOF analyzer to 400 for a 38-cm coaxial reflectron configuration. 

The isomeric o-, m- andp-chloroaniline, which under El give identical spectra, have been characterized by means of resonance-enhanced multiphoton ionization (REMPI) combined with a linear TOF mass spectrometer151. The method is based on the difference the three isomers display in the shapes of their metastable parent ion decays. 

One of the biggest disadvantages of MALDI-TOF MS is its low resolution. For small proteins, the resolution of a linear TOF MS is around 1 500 (i.e., an ion with m/z of 10,000 can be distinguished from an equally abundant ion with a m/z of 10,020). The low resolution is due partly to the fact the ions produced by MALDI do not have uniform kinetic energy, but a distribution of kinetic energies. Thus, ions with the same m/z ratio arrive at the detector at different times giving rise to broad peaks and hence reducing the observed resolution. There are two ways in which the resolution can be increased. 

FIGURE 4 A theoretical calculation of the appearance of the molecular peak of a peptide as it would be observed at different resolutions which correspond to the typical performance of a linear TOF without DE (250), a quadrupolar analyzer (2500), and an FT-ICR (>250,000). (Reproduced with permission from Siuzdak.1 Copyright 1993 National Academy of Sciences, U.S.A.)... 

The major disadvantages of MALDI are (a) the strong dependence of the quality of data obtained on the sample preparation, (b) the low resolution of linear TOF instruments (without DE), and (c) the inability to interface the MALDI ion source directly to HPLC or CE. The advantages of MALDI are ... 

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