Reflectron Instruments

Reports by Chait and co-workers and Demirev et demonstrated that metastable fragmentation of biological molecules (with molecular weights greater than 1 kDa) occurs in a time frame that encompasses their flight times in the drift 

Chapter 3 Reflectrons and Other Energy-Focusing Devices 

FIGURE 3.17 Ion optical system of the Sakurai mass spectrometer. (Reprinted with permission from reference 27). 

Brunelle, A. Della-Negra, S. Depauw, J. Joret, H. Le Beyec, Y., Rapid Commun. Mass Spectrom. 5 (1991) 40-43. 

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The mass accuracy of LSIMS for measurement of the unresolved isotopic cluster is typically within 100 p.p.m. of the calculated average [M+H]+ mass. The accuracy of the observed masses listed in Tables I and II for the MALDI mass spectra benefited from the use of a reflectron instrument which generally reduced the deviation observed between spectra measured under different experimental conditions (e.g. different matrix or laser power) from 1000 p.p.m. to 300 p.p.m. Reflecting this level of mass accuracy we present the MALDI measurements with only 4 significant figures, compared with 5 significant figures for the LSIMS measurements. 

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. 

The PMF data must now be extracted from the MALDI spectrum using the appropriate software associated with the MS instrument used. The baseline threshold should first be adjusted to ensure that all of the peptide signals are detected, without including any noise. If the spectrum has been obtained on a high resolution (reflectron) instrument, the peptide signals will appear as multiple peaks separated by I Da, due to the presence of isotopes in the peptides (see Fig. 2). De-isotoping and centroiding of the MS data is necessary, so that only the monoisotopic peptide masses are included in the PMF data. 

Mass resolution, or the ability of a mass analyzer to separate ion signals from ions of similar mass, is typically 500-800 on a linear TOF. Resolution can be improved in TOF by using a reflectron instrument (18) which compensates... 

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. 

Chapter 8 Product Ion Spectra from Reflectron Instruments... 

Mass Dispersion of Product Ions in a Single-Stage Reflectron. If metastable fragmentation occurs in the first field-free drift region (Zq) of a single-stage reflectron instrument ... 

Post-Source Decay Spectra Using a Dual-Stage Reflectron. The discussion on coincidence techniques above suggests that the opportunities for recording product ion spectra on a reflectron instrument and the necessity for obtaining spectra at different reflectron voltages have been appreciated for some time. Nevertheless, the currendy popular technique known as post-source decay (PSD) is based upon an... 

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