TOF mass analyzer

Most biochemical analyses by MS use either electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALD1), typically linked to a time-of-flight (TOF) mass analyzer. Both ESI and MALDl are "soft" ionization methods that produce charged molecules with little fragmentation, even with biological samples of very high molecular weight. 

Step 5. Automated pyrolysis MS using a novel, highly reproducible ionization mode and a TOF mass analyzer. 

For high-throughput analysis, it is important to increase the specihcity of each bioanalytical method. The enhancement of chromatographic resolution presents various limitations. Better selectivity can be obtained with TOF mass analyzers that routinely provide more than 5000 resolution (full width at half-mass or FWHM). The enhanced selectivity of a TOF MS is very attractive for problems such as matrix suppression and metabolite interference. In one report of quantitative analysis using SRM, TOF appeared less sensitive than triple quadrupole methods but exhibited comparable dynamic range with acceptable precision and accuracy.102... 

A time-of-flight (TOF) mass analyzer separates ions according to the time difference between a start signal and the pulse generated when an ion hits the detector, that is, the time of flight. 

Time of flight (TOF), 75 660-661 Time-of-flight (ToF) mass analyzers, 24 109 Time of flight diffraction (TOFD), 79 486 Time-of-flight instrumentation, in particle counting, 78 150—151 Time-of-flight-SIMS technique, 24 109 Time-resolved fluorimetry, 74 148-149 Time-resolved spectra, analysis of, 74 613 Time standards, 75 749—750 Time-temperature parameters (TTP), 73 471, 478, 479 creep properties and, 73 480 Time-temperature superposition, 27 746-747... 

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.

Laser desorption intrinsically is a pulsed ionization process, which is therefore ideally combined with time-of-flight (TOF) analyzers (Chap. 4.2). [16,49] Ever since the first MALDI experiments, MALDI and TOF have been forming a unit, and the majority of MALDI applications are MALDI-TOF measurements. Vice versa, it was the success of MALDI that pushed forth the tremendous delevopment of TOF mass analyzers. More recently, MALDI has also been adapted to orthogonal acceleration TOF analyzers. [147]... 

With soft ionization techniques such as MALDI, ions of m/z 200000 can be routinely detected. The mass range is mainly limited by the fact that with the detector the response decreases with increasing m/z of the ions. The mass resolution of a TOF mass analyzer is relatively poor (unit mass resolution and less) and is affected by factors that create a distribution in the flight time of ions with the same m/z. The simplest way to increase the mass resolution is to increase the length of flight tube or to reduce the kinetic energy spread of the ions leaving the source. 

In tandem MS mode, because the product ions are recorded with the same TOF mass analyzers as in full scan mode, the same high resolution and mass accuracy is obtained. Isolation of the precursor ion can be performed either at unit mass resolution or at 2-3 m/z units for multiply charged ions. Accurate mass measurements of the elemental composition of product ions greatly facilitate spectra interpretation and the main applications are peptide analysis and metabolite identification using electrospray iomzation [68]. In TOF mass analyzers accurate mass determination can be affected by various parameters such as (i) ion intensities, (ii) room temperature or (iii) detector dead time. Interestingly, the mass spectrum can be recalibrated post-acquisition using the mass of a known ion (lock mass). The lock mass can be a cluster ion in full scan mode or the residual precursor ion in the product ion mode. For LC-MS analysis a dual spray (LockSpray) source has been described, which allows the continuous introduction of a reference analyte into the mass spectrometer for improved accurate mass measurements [69]. The versatile precursor ion scan, another specific feature of the triple quadrupole, is maintained in the QqTOF instrument. However, in pre-... 

The TOF mass analyzer has a low duty cycle, and the combination with an ion accumulation device such as an ion trap is therefore very advantageous. It offers also MS capabilities with accurate mass measurement. In all acquisition modes, the ions are accelerated into the time of flight for mass analysis. Various other hybrid mass spectrometers with TOF have been described, including quadrupole ion trap [70] and linear ion trap [58]. High energy tandem mass spectrometry can be performed on TOF-TOF mass spectrometers [71, 72]. 

The time-of-flight secondary ion mass spectroscopy (ToF-SIMS) analysis was performed on a CAMECA ION-TOF Model IV spectrometer. This instrument was equipped with a reflection-type ToF mass analyzer and a pulsed 25 kV primary... 

Dynamic ion separation systems are based on another physical principle and use the different flight time of ions with different masses and different velocity (e.g., in ToF mass analyzers). In addition, in dynamic ion separation systems there is a time dependent variation of one or more system parameters, e.g., changing of electrical or/and magnetic field strengths, which means the ion motion during the measurement procedure is crucial for the mass spectrometric analysis. 

Dynamic mass separation systems use the fact that ions with different masses (accelerated with the same voltage) possess several velocities and consequently their flight times are different. There are about 50 dynamic separation systems known2 using several types of ion movements (linear straight ahead, linear periodic or circular periodic as a function of the electric or magnetic sector field applied). The simplest dynamic mass separation system is a linear time-of-flight (ToF) mass analyzer, and a widely applied mass separation system is the quadrupole analyzer. 

At present GDMS164 165 is one of the most powerful solid-state analytical methods for the direct determination of trace impurities and depth profiling of solids. The positively charged ions formed in the low pressure argon plasma of the glow discharge are extracted and accelerated into the double-focusing sector field mass spectrometer, quadrupole, ion trap or ToF mass analyzer. 

TOF mass analyzers are based on bombardment by a pulse of electrons or photons to periodically produce positive ions. The pulses have frequencies between 10 and 50 kFIz. The generated ions are then accelerated by an electric sector (voltages from 103 to 104 V) at the same frequency as the ionizing bombardment but with a certain gap. The accelerated ions pass to a 1 m long analyzer rod, which is not subjected to an electrical or magnetic field. As all the ions have the same kinetic energy, their velocities along the analyzer rod must be inversely proportional to the m/z ratio. In this way, those ions with lower m/z ratios reach the detector first. The times to reach the detector (the TOF) are between 1 and 30 ps. 

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