Time-of-Flight Mass Spectrometry TOF-MS

The time-of-flight spectrometry for ERD analysis has been discussed under Sect. 3.4.2 of Chap. 3. The TOF-MS system is employed in AMS, because of the reason that the energy resolution of a silicon detector or an ionization chamber is often insufficient to resolve neighbouring masses of heavier ions. Better separation is possible by combining the energy measurement with a 

The shadowgraphy data in the previous chapter allow the analysis of the products and the shock wave created by the ablation process in air. The shadowgraphy images suggest that only small gaseous products are formed, but no information about the chemical composition of the fragments is obtained by this method. To obtain this information mass spectroscopic methods, such as TOF-MS, must be applied. 

In general, most TOF-MS studies have given strong indications for photo-thermal ablation mechanisms. To test whether a photochemical mechanism could be identified with TOF-MS, we chose a polymer considered photola-bile, which also has excellent properties as a resist for high-resolution microlithography [111, 225-228]. Here we show that the principal products (chiefly N2) from this triazene polymer have components that are much 

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The reaction is believed to proceed predominantly via (34a) to generate chlorine atoms (Molina et al., 1990). However, several groups have reported that the quantum yield for this channel is less than 1.0. For example, Schmidt et al. (1998b) used REMPI with time-of-flight mass spectrometry (TOF-MS) to follow the production of oxygen and chlorine atoms as well as CIO in vibrational levels up to t" = 5 in the photolysis of the dimer. At a photolysis wavelength of 250 nm, the... 

Another use for combinatorial libraries has been the screening of peptides for antimicrobrial properties. In this case, the design of the library is based on antimicrobial peptides found in nature. A combinatorial synthesis is used to find alternative unnatural amino acids expected to mimic the antimicrobial properties.23 Peptide libraries also have been used to find compounds that could bind the lytic peptide mellitin.24 The library was synthesized in solution phase, purified, and evaluated using time-of-flight mass spectrometry (TOF-MS). The sequences determined to bind to mellitin contained hydrophobic pairs. By binding to mellitin, they were able to prevent the cell-surface mellitin interaction. This is an example of a peptide library able to afford compounds that interact with other small peptides without having to find an interacting protein first. 

The detector in capillary electrophoresis is the main component in nanoanalyses. Many detectors can be used for this purpose but the mass spectrometer is the best one due to its wide ranges and low concentration detection capabilities. In the last few years, time-of-flight-mass spectrometry (TOF-MS) instruments have come onto the market and are available in many sizes, but small instruments are preferred in NCE. Bruker (Billerica, MA) has provided a micro-TOF-MS-LC (2x2x4 feet) system for nanoanalyses. Bruker also introduced a Q-q-FTMS (Fourier transform mass spectrometer) for proteomics called the APEX-QE. It offers fast, dual quadrupoles, which provides the first stages followed by FTMS for the highest mass accuracy. It can be coupled to NCE and controlled by Bmker s ProteinScape work flow and warehousing... 

Gottardo R, Polettini A, Sorio D, Pascali JP, Bortolotti F, Liotta E, Tagliaro F (2008) Capillary zone electrophoresis (CZE) coupled to time-of-flight mass spectrometry (TOF-MS) applied to the analysis of illicit and controlled drugs in blood. Electrophoresis 29(19) 4078 1087. doi 10.1002/elps.200800087... 

Figure 3 Postacceleration beam sweeping mode for continuous ion-beam modulation in an on-axis time-of-flight mass spectrometry (TOF-MS) geometry. 1, 2, deflection plates V, deflection voltage t, time , ions reaching detector 0, ions not reaching detector.

Figure 4 Orthogonal time-of-flight mass spectrometry (TOF-MS) in a nonextraction mode (top) and extraction mode (bottom).

Finally, the development of fast GC [61-63] and comprehensive two-dimensional GC (GC X GC) [64-66] address the continuous demand for increased speed and separation power in routine analysis. The former technique allows a dramatic reduction in analysis time without sacrificing resolution, while the latter offers a markedly increased separation power without altering the analysis time. A fast GC method for the analysis of cocaine and other drugs of forensic relevance has been published by Williams et al. [67]. They used a GC instrument in which the column was resistively heated at rates of up to 30°/s which allowed separation of 19 compounds within 1.5 min. A GC x GC time-of-flight mass spectrometry (TOF-MS) method has been proposed by Song et al. [68] for the analysis of a mixture of 78 drugs of interest, including cocaine and benztropine. 

Most investigations of photoinduced electron transfer have been performed in condensed phases. Much less is known about conditions that permit the occurrence of intramolecular ET in isolated (collision-free) molecular D-A systems. A powerful method for this kind of study is the supersonic jet expansion teehnique (which was originally developed by Kantrowitz and Grey in 1951 [66]) combined with laser-induced fluorescence (LIF) spectroscopy and time-of-flight mass spectrometry (TOF-MS). On the other hand, the molecular aspects of solvation can be studied by investigations of isolated gas-phase solute-solvent clusters which are formed in a supersonic jet expansion [67] (jet cooling under controlled expansion conditions [68] permits a stepwise growth of size-selected solvation clusters [69-71]). The formation of van der Waals complexes between polyatomic molecules in a supersonic jet pro-... 

D. Electrospray Ionization and Time-of-Flight Mass Spectrometry (TOF/MS)... 

In the absence of field, ions fly by inertia with conserved v. These two facts are exploited in time-of-flight mass spectrometry (TOF MS), where ions are accelerated in a pusher region to different v depending on y m/z and fly through a field-free space of well-defined length to the detector. " The measured flight time through that space reveals v and thus m/z of ions present. 

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