Reflectron voltage

Mass spectra were collected on a Bruker Reflex II-MALDI-TOF mass spectrometer (Billerica, MA) equipped with delayed extraction and a N2 laser (337 nm). In the positive reflectron mode, an accelerating voltage of 25.0 kV and a reflectron voltage of 26.5 kV were used. Spectra are the sum of 50-300 shots. Spectra were calibrated with bradykinin (1060.6 MW) and glucagon (3483.8 MW) as external standards. 

In current instruments, two modifications from a simple tof instrument are included. One is the reflectron, a set of ion mirrors which slow the ions down, reverses their direction, and by increasing the actual length of the flight path, increases the resolution. See Figure 2 for a schematic of an instrument with a reflectron. By appropriate choice of reflectron voltages and shape of the voltage fields, one can improve resolution even more. This is described in detail in other references (18). The overall effect of the reflectron is to make little change in equation (2) for use as a calibration equation. 

FIGURE 8.1 Linear and reflectron modes for recording time-of-flight mass spectra, (a) by switching the reflectron voltage, and (b) by deflecting the ion beam. 

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... 

FIGURE 8.6 (a) Molecular-ion region mass spectrum of a mixture of tyrocidin A, B, and C, obtained in the linear mode with the reflectron voltage turned off, (b) molecular-ion region obtained in the reflectron mode, (c) neutral mass spectrum of the molecular-ion region with the reflectron voltage turned on, (d) correlated product-ion mass spectrum of tyrocidin A, and (e) correlated product-ion mass spectrum of tyrocidin B. (Reprinted with permission from reference 7). 

FIGURE 8.9 Post-source decay mass spectra of Substance P recorded at different values of the reflectron voltage. (Reprinted with permission from reference 8). 

FIGURE 8.11 Post-source decay mass spectra of a mixture of Substance P and bombesin, (a) Mass spectrum without precursor-ion selection at full reflectron voltage, (b) Selection of the MK ion of Substance P. (c) Selection of the MH ion of bombesin. (Reprinted with permission from reference 3). 

When more than one peptide is present, ion gating is required as shown in Figure 8.11. In these spectra, obtained at fvill reflectron voltage, both focused and small PSD fragments are observed for each component, but can be separated by the application of an ion gate. Figure 8.12 shows the assembled product ion mass spectrum of bombesin obtained from this mixture from 12 mass-spectral segments. 

FIGURE 8.15 Post-source decay mass spectrum of coli thioredoxin obtained from a single-stage reflectron TOP mass spectrometer in two reflectron voltage segments. (Reprinted with permission from reference 10). 

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