Time-of-flight TOF mass spectromete

Hybrid time-of-flight (TOF) mass spectrometers make use of a TOF analyzer placed at right angles to a main ion beam. Ions are deflected from this beam by a pulsed electric fleld at right angles to the ion beam direction. The deflected ions travel down the TOF tube for analysis. Hybrid TOF mass spectrometers have many advantages arising from the combination of two techniques, neither of which alone would be as useful. 

In a time-of-flight (TOF) mass spectrometer, ions formed in an ion source are extracted and accelerated to a high velocity by an electric field in an analyzer consisting of a long, straight drift tube. The ions pass along the tube until they reach a detector. 

In time-of-flight (TOF) mass spectrometers, a pulse of ions is accelerated electrically at zero time. Having attained a maximum velocity, the ions drift along the flight tube of the analyzer. The times of arrival of ions at a detector are noted. 

The output of a Nd YLF laser is focussed by a series of lenses to a spot size of 0.5 pm upon a sample which may be positioned by an x-y-z stepping motor stage and scanned by a computer-controlled high frequency x-y-z piezo stage. Ions are accelerated and transmitted through the central bore of the objective into a time-of-flight (TOF) mass spectrometer. The laser scans an area of 100 x 100 pm with a minimum step size of 0.25 pm. TOF mass spectra of each pixel are evaluated with respect to several ion signals and transformed into two-dimensional ion distribution plots. 

Figure 2.3. A. Mass spectrometer consisting of an ionization source, a mass analyzer and an ion detector. The mass analyzer shown is a time-of -flight (TOF) mass spectrometer. Mass-to-charge (m/z) ratios are determined hy measuring the amount of time it takes an ion to reach the detector. B. Tandem mass spectrometer consisting of an ion source, a first mass analyzer, a collision cell, a second mass analyzer and a detector. The first mass analyzer is used to choose a particular peptide ion to send to the collision cell where the peptide is fragmented. The mass of the spectrum of fragments is determined in the second mass analyzer and is diagnostic of the amino acid sequence of the peptide. Figure adapted from Yates III (2000).

As the laser pulse is in the nanosecond range, a fast mass spectrometer has to be coupled in series. In most cases, MALDI is coimected to a time-of-flight (TOF) mass spectrometer with which m/z ratios are determined by precisely measuring the time an ion needs to pass from the ion source to the detector. Besides its abil-... 

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 ... 

The experiments of Kistiakowsky and Kydd [1] were done by single-pulse photolysis with a 500-J flashlamp, the reaction vessel contents being sampled via a pinhole leak into the electron ionization source of a Bendix time-of-flight (TOF) mass spectrometer. Mass spectra were obtained by pulsed extraction of ions from the ion source at 50-fis intervals after the flash. The signal from the electron multiplier detector was displayed on a cathode ray tube, which was photographed with a rotating drum camera. 

The quantum yield of 0( P) has been determined by resonance absorption at 130 nm (76), resonance fluorescence (73,75), and time-of-flight (TOF) mass spectrometer (72,74). The quantum yield of 0(1d) decreases from 0.9 to 0.1 in the 300 to 320 nm region (73). The production of 0(ls) is 0.1% or less in the entire region from 170 to 240 nm (78). Above 310 nm both 03 absorption and the 0(1d) quantum yield increase with vibrational excitation of O3 (79). For example at 314 nm, which is about 500 cm-l below the thermochemical threshold for process (32), the absorption cross section increases more than 8 times and the quantum yield increases 6 times. 

Several scan modes are unique to the triple-quadrupole instrument, and most of these modes are superior in duty cycle versus an ion trap, Fourier transform (FT), or time-of-flight (TOF) mass spectrometers. Different elements of the triple-quadrupole perform different operations for each scan mode. These scan modes, each of which will be described in detail, are single-reaction monitoring (SRM) or multiple-reaction monitoring (MRM), precursor ion scanning (PIS), and constant-neutral-loss scanning (NLS). These scan modes and applications for structural elucidation have been described in detail (Yost and Enke, 1978, 1979). 

Voyager DE MALDI time of flight (TOF) mass spectrometer (Applied Biosystems). 

The application of time-of-flight (TOF) mass spectrometers to SIMS was first reported by Chait and Standing in 1981 [50]. Their instrument used a pulsed alkali metal ion source and a linear flight tube. Steffens et al. developed an im-... 

The femtosecond laser pulses shaped by the AOPDF are amplified by the CPA up to 0.5mJ/pulse. Ethanol vapor is continuously flow into the vacuum chamber through a micro-syringe (70 pm) with stagnation pressure of 7 Torr at room temperature. The laser pulses are focused on a skimmed molecular beam of the ethanol vapor with an achromatic lens (/ = 145 mm). The focal spot size of the laser beam is 20 pm(j>. The peak intensity of the transform-limited laser pulse is calculated to 4 x 1015 W/cm2. The fragment ions are mass-separated with Wiley-McLaren type time-of-flight (TOF) mass spectrometer, and are detected with a microchannel plate (MCP) detector. 

FTICR, magnetic sector, and time-of-flight (TOF) mass spectrometers are also capable of acquiring accurate mass measurements on molecular and fragment ions from both GC/MS and LC/MS experiments on trace level impurities. Applications of FTICR LC/MS... 

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