Resolution Orbitrap analyzer

Advances in high resolution mass analyzers (TOF, FT-ICR, orbitrap) have greatly improved the detection and identification of metabolites based on accurate mass measurements. In single MS mode accurate mass determination is mainly used to differentiate between isobaric ions. Combined with LC-MS, it allows the detection of predicted metabolites by performing extracted ion current profiles... 

Orbitrap The newest of the major mass analyzers, the Orbitrap is a hybrid MS consisting of a LIT mass analyzer, or transmission quadmpoles connected to the high-resolution Orbitrap mass analyzer. The Orbitrap utilizes electrical fields between sections of a roughly egg-shaped outer electrode and an inner (spindle) electrode (Chapter 5). Ions orbit between the inner and outer electrodes and their oscillation is recorded on detector plates (Hardman and Makarov, 2003 Hu et al., 2005). As with the FTICR, fast Fourier transform of the raw data is used to convert the data for mass analysis, making the Orbitrap the second major type of FTMS instrument. The resolving power of the Orbitrap is intermediate... 

Other mass analyzers, especially those providing high-resolution, such as time-of-flight (ToF), Orbitrap and Fourier-transform ion cyclotron resonance MS, have been applied scarcely. Two biotransformation studies were carried out with a QqTOF-MS/MS, these advantages were used in order to gather accurate masses of metabolites [17, 60] and recently, the ultra-high resolution Orbitrap MS has been applied to confirm the presence of novel metabolites [21],... 

In another work [73], the better analytical performance of an UHPLC—Orbitrap method over a previously published TOF-based method is demonstrated [69] for the determination of more than 100 veterinary drugs in difficult matrices (muscle, kidney, liver, fish, and honey). These improvements are attributed to the combination of a more effective sample preparation with the higher resolution (50,000 versus 12,000 fwhm) and superior mass stability of the Orbitrap analyzer over the previously used TOP instrument. 

Both ionization methods, MALDI and ESI, are adequate for the analysis of low-and high-molecular-weight molecular ions. Data provided by mass-to-charge ratio (m/z) determination can in some cases directly depict a compositional assignment of the molecule under investigation if the resolution and mass accuracy are sufficient, as in quadrupole TOF (QTOF) analyzers, or high, as in ion cyclotron resonance (ICR) and Orbitrap analyzers. 

The orbitrap analyzer itself does not provide for a mode of tandem MS operation. Instead, the steps of precursor ion isolation and dissociation are performed in a dedicated LIT as MSI (Chap. 4.8.4) prior to high-resolution and accurate mass analysis of the fragments by the orbitrap. Multiple-collision CID (Chap. 9.3) in the LIT of the LTQ-orbitrap instrument is sometimes not hard enough to achieve fragmentation of comparatively stable precursor ions, e.g., it can be insufficient to generate immonium ion fragments from protonated peptides. 

In a LTQ-Orbitrap MS, where the high-resolution mass analyzer is usually combined with a linear ion trap, accurate mass measurements are combined with the high trapping capacity and MS scan function of the hnear ion trap. Therefore, the LTQ-Orbitrap is capable of MS/MS and produces very high accuracy mass data (within 2 ppm using internal standard and within 5 ppm with external calibration (Makarov et al. 2006)) which makes it a useful instrument in identification of transformations or transformation products (Hu et al. 2005 Lim et al. 2007 Ruan etal.2008). 

The orbitrap is the most recently invented mass analyzer. Like with the QIT, ions are trapped and stored in a potential well. However, instead of ejecting the ions for external detection the frequency of the trapped oscillationg ions is measured. This method provides substantially better resolution and mass accuracy in normal operation. 

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). 

Schmid, D. G., Grosche, P., Bandel, H., and Jung, G. (2000). FTICR-mass spectrometry for high-resolution analysis in combinatorial chemistry. Biotechnol. Bioeng. 71 149-161. Scigelova, M., and Makarov, A. (2006). Orbitrap mass analyzer—Overview and applications in proteomics. Proteomics 6 (Suppl. 2) 16-21. 

ESI mass spectrum of bovine insulin obtained with an orbitrap. The resolution at m/z 1149 is more than 60000 FWHM. Additional peaks are due to the presence of Ultramark 1621 as internal standard. Reproduced from Hu Q., Makarov A., Noll R.J. and Cooks R.G., Application of the Orbitrap Mass Analyzer to Biologically Relevant Compounds , Proceedings of the 52nd ASMS Conference, Nashville, Tennessee, 2004, with permission. 

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