Reflectron instrument design

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... 

Notable among the instrumental design characteristics is the use of direct current (dc) quadrupole lenses to limit ion-beam width spatially within the extraction region. These lenses, along with the use of an ion reflectron, provided resolving powers of approximately 1600 (FWHM) [40]. An illustrative spectrum of Pb and Bi obtained with this instrument is provided as Fig. 12.10. 

Due to the pulsed nature of most of these experiments, much of the work to date has been performed using time-of-flight mass spectrometers. Quadrupole mass spectrometers are also well suited, especially with higher duty cycle systems. Design of the instruments has followed conventional approaches, for which the resolution limits the size and complexity of the cluster and cluster-adduct species that can studied. One serious problem is the isotopic abundance of many of the metals, which serves to complicate mass spectra. Isotopi-cally pure materials, such as used in measurements of hydrogen uptake on Fe clusters, " simplify the mass spectra. Use of the reflectron time-of-flight mass spectrometer allows the study of metastable clusters and cluster adducts. Details of different instrument designs are described in the references. 

The conceptual simplicity of TOF-MS disappears when one considers actual instrumentation design. A good understanding of this issue is important in the selection and use of TOP mass spectrometers because there is a good deal of confusion about the true significance of terms like hnear, reflectron, orthogonal acceleration, delayed extraction, and so forth. This may lead to poor selection and use of instriunents. 

The mass range of commercial TOF instruments is up to 10,000 Da. Resolution depends on the type of TOF and ranges from 1000 for instruments designed as dedicated detectors for GC (GC-TOFMS) to 20,000 for reflectron instruments. One limitation to the use of a conventional reflectron instrument is a loss in sensitivity about 10% of the ions are lost with a conventional wire grid reflectron. 

Electric sectors have not enjoyed anywhere near the same popularity as reflectrons in time-of-flight design. Isochronous systems, particularly those involving multiple sectors, are more difficult to design. In addition, reflectron instruments provide an important opportunity for recording the structural information provide by postsource decay, which is now being utilized for the amino acid sequencing of peptides. 

Hieftje and co-workers first reported a design for ICP-ToF mass spectrometric systems with both orthogonal acceleration (oa) and axial acceleration (aa) geometry.39 11 The different experimental setups of ICP-ToF mass spectrometers with orthogonal and axial acceleration are compared in Figures 5.10 and 5.11. Both instruments possess a time-of-flight analyzer with a reflectron to improve the mass resolution. 

Ehlers, M. Schmidt, S. Lee, B.J. Gro-temeyer, J. Design and Set-Up of an External Ion Source Coupled to a Quadru-pole-Ion-Trap Reflectron-Time-of-Hight Hybrid Instrument. Eur. J. Mass Spectrom. 2000, 6, 377-385. 

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