LTQ Orbitrap

FIGURE 5.2 Ion path for LTQ-Orbitrap. (Courtesy of Thermo Fisher Scientific, Waltham, Massachusetts.)... 

MS11 capabilities. However, ions may then subsequently be detected at unit resolution using an electron multiplier or, alternatively, focused in a C-Trap (Figure 5.2) and then transferred and detected at high resolution using the Orbitrap. In our experience with the LTQ-Orbitrap, ions may be measured with a resolution of approximately 60,000 with online LC/MS in the full scan mode. 

A. Makarov, E. Denisov, O. Lange, and S. Homing. Dynamic Range of Mass Accuracy in LTQ Orbitrap Hybrid Mass Spectrometer. J. Am. Soc. Mass Spectrom., 17(2006) 977-982. 

Fig. 1.30 Schematic of the linear ion trap (LIT)-orbitrap (LTQ orbitrap, Thermo). One of the specificities of the system is that the LIT has two detectors. Therefore the LIT can perform various experiments at the same time. Adapted with permission from reference [76].

Figure 4.1 Separation of H3 9-17 trimethylated subsequentlydigested with trypsin. The resulting at l<9 from H3 9-17 monoacetylated. Histone peptides were analyzed by LC-MS/MSemploying H3 isolated from Drosophila melanogaster was LTQ-Orbitrap (Thermo Scientific) as detector, acylated with deuterated acetic anhydride and (a) Chromatogram of the analysis. The y axis...

The Orbitrap-based systems have emerged as the newest option for LC-HRMS. When configured as hybrid linear trap-Grbitrap (LTQ-Orbitrap), the systems are conceptually similar to Q-TOF in that mass analyzer 1 is nominally a unit mass analyzer, and mass analyzer 2 is capable of high resolution. These systems are capable of either LC-HRMS or LC-MS/HRMS operation. A new variant on the commercial Orbitrap, the Exactive, is expected to be released in late 2008. This system, which consists only of the single mass analyzer, has shown promising results in early assessment of quantitation by LC-HRMS (Bateman et al., 2008). 

Erve, J. C. L., DeMaio, W., and Talaat, R. E. (2008). Rapid metabolite identification with sub parts-per million mass accuracy from biological matrices by direct infusion nanoelectrospray ionization after clean-up on a ZipTip and LTQ/Orbitrap mass spectrometry. Rapid... 

Due to its radically different design, the latest hybrid linear ion trap FTMS instrument, the LTQ-Orbitrap (Fig. 5.6), does not suffer from the time-of-flight effect. In this instrument, the superconducting magnet and the ICR cell are replaced by an electrostatic trap (C-trap) and so distances traveled by the ions from one MS device to the other are much smaller in addition a radically different ion transfer mechanism virtually eliminates any possibility for a time-of-flight effect (Makarov,... 

Figure 5.6. Schematic of a hybrid LTQ-Orbitrap mass spectrometer (a) transfer octapole (b) curved rf-only quadmpole (C-trap) (c) gate electrode (d) trap electrode (e) ion optics (f) inner orbitrap electrode (g) outer orbitrap electrodes (Makarov et at., 2006a).

Hardman and Makarov, 2003), making the LTQ-Orbitrap especially suitable for small-molecule analyses. For most compounds, the relative intensities of ions in Orbitrap mass spectra are very similar to those spectra from LTQ (IT scan) (Fig. 5.5) (Sanders et al., 2005). As discussed above, this feature becomes very important for building MS/MS libraries and subsequent library searches for related structures (i.e., metabolites, structural analogues, degradants, etc.). Also highlighted in Fig. 5.5 are the excellent mass accuracies observed in the MS/MS mode, even for some very minor fragments. 

The LTQ-Orbitrap has resolution and mass accuracy performance close to that of the LTQ-FTICR. As shown in Table 5.3 (column 4), LTQ-Orbitrap accurate mass measurements, using external calibration, for a set of 30 pharmaceutical compounds resulted in less than 2.3 ppm error. The data were acquired with a 4-min, 1-mL/min-flow-rate, positive-mode LC-ESI-MS method where all measurements were performed within 5h from mass calibration. Mass accuracies below 2-3 ppm, and often below 1 ppm, can be routinely achieved in both the positive- and negative-ion mode (Table 5.3, columns 4 and 5). The long-term mass stability of the LTQ-Orbitrap is not as consistent as observed for the LTQ-FTICR-MS, and the Orbitrap requires more frequent mass calibration however, mass calibration is a routine procedure that can be accomplished within 5-10 min. Figure 5.7 displays a 70-h (external calibration) mass accuracy plot for three negative ions collected with a LTQ-Orbitrap where the observed accuracy is 2.5 ppm or better with little mass drift for each ion. Overall, for routine accurate mass measurements on the Orbitrap, once-a-week calibration (for the desired polarity) is required however, considering the ease of the process, more frequent external calibration is not a burden. 

The sensitivity of the LTQ-Orbitrap is demonstrated using a mixture of synthetic standards of buspirone metabolites spiked into a rat plasma extract. The samples were analyzed with a standard 4.6-mm HPLC column. LC-MS/MS chromatograms for the five-component mixture obtained using the Orbitrap and the LTQ mass spectrometers are compared in Figs 5.8a and h. Also shown are MS/MS (m/z 402) spectra of the oxa-buspirone metabolite (R, = 7.4 min) at 10 pg on column in the Orbitrap (Fig. 5.8c) and LTQ (Fig. 5.8e). As discussed above, the MS/MS fragmentation spectra, obtained in the Orbitrap (Figs 5.8c and d), are very similar to those from the LTQ (Fig. 5.8e), and even at such low concentrations excellent mass accuracies are maintained. 

Chen, G., Khusid, A., Daaro, I., Irish, P., and Pramanik, B. N. (2007). Structural identification of trace level enol tautomer impurity by on-line hydrogen/deuterium exchange HR-LC/MS in a LTQ-Orbitrap hybrid mass spectrometer. J. Mass Spectrom. 42 967-970. 

Lim, H. K., Chen, J., Sensenhauser, C., Cook, K., and Subrahmanyam, V. (2007). Metabolite identification by data-dependent accurate mass spectrometric analysis at resolving power of 60,000 in external calibration mode using an LTQ/Orbitrap. Rapid Commun. Mass Spectrom. 21 1821-1832. 

Makarov, A., Denisov, E., Lange, O., and Homing, S. (2006b). Dynamic range of mass accuracy in LTQ Orbitrap hybrid mass spectrometer. J. Am. Soc. Mass Spectrom. 17 977-982. 

Lee, L., McLaughhn, T., Chen, Y., Ma, J., Cho, R., Le, H., and Miao, S. (2007). Re-interrogation of verapamil metabolites from bile using time-based data-dependent mass fists and mass defect filter with the LTQ Orbitrap. In Proceedings of the 55th ASMS Conference on Mass Spectrometry and Allied Topics, Indianapolis, IN. 

Nevertheless, even with accurate mass measurement by Q-TOF, LTQ-Orbitrap, or LTQ-Fourier transform ion cyclotron resonance (LTQ-FTICR) MS, it is not always possible to fully characterize certain metabolites based solely on mass spectrometric... 

Q-TOF, LTQ-Orbitrap ESI negative and positive ion mode Full-scan MS, PIS, MRM NanoMate (19)... 

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