Timed ion selector

Fig. 4.16. Tandem TOF analyzer with linear TOFl and ReTOF2. The ions from TOFl are passed into ReTOF2 by a timed ion selector. Reproduced from Ref. [64] with permission. Elsevier Science, 2002.

Several commercial instrument designs have effectively overcome this inherent problem and can record high-energy CID product ion spectra. The Applied Biosystems 4700 Proteomics Analyzer was one of the two originally available commercial TOF/TOF designs76,77 (Fig. 24). When the instrument is operated to obtain a mass spectrum, it acts as a standard inline reflectron TOF instrument. In product ion experiments the precursor ion is isolated at the end of the first flight tube by the timed-ion selectors (TIS). The MALDI source uses DE to correct for... 

A final type of tandem-in-space spectrometer is the TOF-TOF spectrometer, in which a TOF instrument followed by a timed ion selector separates the precursor ions. A collision cell then induces fragmentation, and the product ions are mass analyzed in the final TOF stage.Mass resolution of several thousand was reported. 

The combination of two analyzers in a TOF/TOF overcomes the problems with the detection of PSD ions. The separation attained with the first analyzer enables the selection of an ion of interest using an electronic gate called a timed ion selector (TIS). The selected ion is then fragmented in a collision cell, followed by analysis of the fragments in a second TOF analyzer (Figure 2.35). The calibration of TOF 1 (with known compounds) permits the prediction of the arrival time of the... 

Ions selected in the timed ion selector (TIS) are retarded and then subjected to CID in the collision celL... 

Figure 25.2 (bottom panel) contains the MS/MS spectrum of thioredoxin with the precursor suppressor ON and optimized for precursor (10,000 laser shots). The data collected were with the default MS-MS 2 kV Positive Sensitivity operating mode with the CID OFF (i.e., no target gas in collision cell) and the timed ion selector (TIS) set at a resolution of 100 Da with a 1.0 bin size for the digitizer. 

Another very important feature ofTOF/TOF and Q-TOF instmments for gaining deeper insight in stmctures of bio- and synthetic polymers is provided by their ability to perform MS/MS (also known as tandem MS or MS") experiments. Ions of interest (precursor ions) are selected either by means of the quadmpole filter in a Q-TOF or by a precursor ion selector (e.g., just by opening a time window ) in a TOF/TOF instm-ment. These precursor ions pass a collision cell filled with a collision gas. Thus, the fragmentation of precursor ions into... 

FIb.1. Schematic diagram of the apparatus. A continuous supersonic Hg/Ar expansion produces the clusters. They can be ionised by electron or i oton impact. An electric pulse between the plates IH) and PI accelerates ions into the time-of-fiight mass spearometer. The first time focus is at the slit of the mass selector, the second is at the detector II. The mass selector can be used to select one mass only, say Hgjo, which can subsequently decay in the free-flight region into Hg, + Hg due to internal excitation. The reflector can separate parent (n = 20) and daughter (r — 19) cluster ions. 

In neutron TOF experiments, the neutron source is a burst of neutrons generated either by a velocity selector (chopper) or by an ion beam, as explained later in this section. The time-of-flight t is the difference between the time of production of the neutron burst and the time of neutron detection. 

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