Linear Trap Quadropole (LTQ) Orbitrap Velos Mass Spectrometry
LTQ Orbitrap Velos is a hybrid mass spectrometer incorporating the LTQ Velos™ dual cell linear trap and the Orbitrap™ analyzer. The LTQ Orbitrap is a high performance LC-MS and MSn system, combining rapid LTQ ion trap data acquisition with high mass accuracy Orbitrap mass analysis. Significantly, the Orbitrap XL ETD includes two fragmentation regimes, higher-energy C-trap dissociation (HCD) and electron transfer dissociation (ETD), that are complementary to the LTQ’s collision induced dissociation (CID) option. These additional, alternative fragmentation capabilities are essential for the success of the diverse projects focused on phosphoproteomics; posttranslational modification analyses and “middle-down” proteomics.
In an orbitrap mass analyzer, ions are trapped in an electrostatic field between an inner and outer electrode (Makarov, 2000). As the ions rotate around the inner electrode, they precess along its axis with a frequency characteristic of their mass-tocharge (m/z) ratio. Acquisition of transients and the Fourier transformation of that signal yields frequencies and their intensities. A simple relationship converts frequencies into m/z values. The LTQ-Orbitrap hybrid mass spectrometer is a high mass accuracy, high resolution mass analyzer, capable of achieving resolving power > 100,000 and having mass accuracy ≤ 5 ppm (Makarov et al., 2006). Employing a simple lock-mass scheme can reduce mass errors to less than 2 ppm (Olsen et al., 2005). The “higher-energy C-trap” dissociation (HCD) method was introduced as a fragmentation process that overcomes two of the shortfalls when performing CID in the LTQ ion trap, namely [1] low mass resolution and accuracy, and [2] losses due to “low mass cutoff” (Olsen et al., 2007). In the following year came the report of the introduction of electron transfer dissociation (ETD) regimes to the LTQ-Orbitrap (McAlister et al., 2008). In ETD, an anion donates an electron to a cationic peptide, which then causes the peptide backbone to fragment (Syka et al., 2004). ETD is of significant usefulness in proteomics because of its ability to preserve most posttranslational modifications of general interest (PTMs; Swaney et al., 2009).
The distinct benefits of the Orbitrap XL ETD mass spectrometer are its high sensitivity, resolution and mass accuracy, coupled to a fast scan rate. To adequately inventory the protein constituents within a complex proteomic sample, high quality data most be acquired on a time scale consistent with nano-liquidchromatographic separation and elution.
- Makarov A. (2000) Electrostatic axially harmonic orbital trapping: a high-performance technique of mass analysis, Anal Chem 72, 1156-1162.
- Makarov, A., Denisov, E., Kholomeev, A., Balschun, W., Lange, O., Strupat, K., and Horning, S. (2006) Performance evaluation of a hybrid linear ion trap/orbitrap mass spectrometer, Anal Chem 78, 2113-2120.
- Olsen, J. V., de Godoy, L. M., Li, G., Macek, B., Mortensen, P., Pesch, R., Makarov, A., Lange, O., Horning,S., and Mann, M. (2005) Parts per million mass accuracy on an Orbitrap mass spectrometer via lock mass injection into a C-trap, Mol Cell Proteomics 4, 2010-2021.
- Olsen, J. V., Macek, B., Lange, O., Makarov, A., Horning, S., and Mann, M. (2007) Higher-energy C-trap dissociation for peptide modification analysis, Nat Methods 4, 709-712.
- Swaney, D. L., Wenger, C. D., Thomson, J. A., and Coon, J. J. (2009) Human embryonic stem cell phosphoproteome revealed by electron transfer dissociation tandem mass spectrometry, Proc Natl Acad Sci U S A 106, 995-1000.
- Syka, J. E., Coon, J. J., Schroeder, M. J., Shabanowitz, J., and Hunt, D. F. (2004) Peptide and protein sequence analysis by electron transfer dissociation mass spectrometry, Proc Natl Acad Sci U S A 101, 9528-9533 .