Resolving Orbitrap

Figure 2.7 Mass spectra recorded at different resolutions. Mass spectrum obtained by a two dimensional ion trap at low resolution (a) and by an Orbitrap at resolving power 50000 (b). Mass spectrum of a mixture of three isobaric species [C19H7N]+, [C20H9]+, [C13H19N302]+ obtained at low resolution (black line) and at resolving power 50000 (grey line) (c). It is noteworthy that at low resolution the three peaks are completely unresolved...

The Orbitrap allows very high resolution to be achieved (the resolving power in commercial instruments is 100000, rivalling that of FT-ICR instruments) and routine mass measurement accuracies less than 2 ppm. It finds applications in many fields, such as biology, proteomics, food chemistry and cultural heritage. 

The acquisition speed is, as for the FTICR, resolution dependent. With Thermo Fischer Scientific s orbitrap the desired mass resolving power can be selected. With the lowest setting (7500 FWHM) the acquisition time for one ion injection is 0.3 s and with the highest setting (100,000 FWHM) it is 1.9 s. 

A mass calibration for FTICR analyzers with superconducting magnets is very stable and is valid for many days for normal applications. Mass accuracy < 1 ppm can be obtained over a fairly wide mass range. Unique elemental composition can be determined for masses over 800 Da [262]. Recently, 0.1 ppm mass accuracy, which required a mass resolving power >300,000, has been achieved for several thousand peaks by a 14.5 T instrument [263] and commercial instruments with mass accuracy <0.2 ppm are available. As with the orbitrap (see Section 2.2.5) the frequency is... 

The modem sector instruments have resolving power about 60,000 to 80,000, and in some cases up to 150,000. There are reports of resolution about 70,000 in the case of ion traps. The newly developed (2005) Orbitrap instruments demonstrated resolving power up to 200,000. Super high resolution (dozens of millions) may be achieved using FTMS (FTICR). 

With time of flight instruments, a mass accuracy better than 5 ppm can be achieved, while with Fourier transform ion cyclotron resonance or orbitrap mass spectrometers mass accuracies better than 1 ppm have been reported. It is obvious that, for good mass accuracies, the peaks must be baseline resolved and resolution plays an essential role. For the present example, a mass resolving power of 5000 seems to be quite acceptable. In the case of the [M+H]+ + 1 isotope peak, the situation becomes somewhat more complex for molecules containing nitrogen, sulfur or carbon. Figure 1.5 D illustrates at a mass resolving power of 500000 the contribution of... 

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... 

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. 

A + 2 of protonated MRFA peptide measured with a resolving power of 100 000 with an orbitrap mass spectrometer. The peaks due to the indicated isotope compositions are clearly separated and measured with correct relative abundances. Redrawn, with permission from Thermo-Finnigan documentation. 

ToF analyzers as well as hybrid instruments that combine two or more mass-resolving components, such as quadrupole-ToF (Q-ToF), ion-mobility ToF, and ion-trap-ToF, as well as the high-resolving Fourier transform (FT) analyzer Orbitrap and ion cyclotron resonance (ICR). For targeted analysis, a multiple-reaction monitoring instrument based on triple-quadrupole technologies (QQQ) has provided unrivaled sensitivity for MSI of pharmaceuticals, yet its targeted nature renders it unsuitable for discovery-based research. 

Lim et al. [93] investigated the use of LTQ-Orbitrap to identify human liver microsomal metabolites of carvedilol, using parent mass list triggered data-dependent multiple stage accurate mass analysis. In this study, LTQ-Orbitrap was used for accurate mass measurements at a resolving power of 60,000 to obtain mass accuracy <2 ppm for all full-scan and MS" spectra in the external calibration mode. The chemical formulas obtained from high-resolution accurate mass measurements were used to confirm structures of the product ions proposed by Mass Frontier. 

An Orbitrap mass spectrometer, as a result of its outstanding mass resolving power, high sensitivity, accurate mass measurement (<5 ppm), full-scan, and/or MS" capabilities, is an attractive alternative to a TOF instrument, especially for analysis of small molecules (m/z < 1000). The Orbitrap... 

The selection of resolving power in an Orbitrap must be fit for purpose and is associated with both the analyte concentration and the complexity of matrices. A study " indicated that a resolving power of 7,000-10,000 could be sufficient for detection of analytes in samples of intermediate complexity at concentrations down to 25 (Tg/kg with accurate mass measurement (mass errors <5 ppm) for lower concentration levels and/or more accurate mass assignment, a higher resolving power (18,000-25,000) was needed and in highly complex extracts, a resolving power of 35,000-50,000 or even... 

Analyze by direct infusion using a Q Exactive Hybrid Quadrupole-Orbitrap mass spectrometer (ThermoFisher Scientific). AH analyses are performed with resolving power set to 140,000, four microscans for 30 s. 

Top-down sequencing of the denatured and reduced protein was analyzed by direct infusion using a Exactive Hybrid Quadrupole-Orbitrap mass spectrometer with a resolving power of 70,000. 

The order of increasing resolution (including typical values) for the different types of analyzer is quadrupole (unit) < time-of-fiight (to 60,000) < orbitrap (to 250,000) < FT-ICRMS (to 3,000,000), where unit is the ability to resolve mass X from mass X+1 throughout the mass range (Figure 3.2). Associated with resolution, and shown in the figure, is the term peak capacity, the number of peaks that can be fitted in between two adjacent masses. As resolution increases so does peak capacity. 

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