Analyzers, mass ion cyclotron resonance

In a commercially available device based on Penning traps - the Fourier transform ion cyclotron 

The radius of ion trajectory in the Penning trap is then determined by  

Fourier transform ICR mass spectrometers together with any type of ion source, such as nanoESI, MALDI (or also an inductively coupled plasma ion source) permit mass spectrometric measurements to be performed at ultrahigh mass resolution (R = m/hm = 105—106) with a very low detection limit and the highest possible mass accuracy (Am = 10 3—10 4 Da). In addition, a high mass range is possible and FTICR-MS can be applied for MS/MS experiments.48 A comparison of different separation systems used in inorganic mass spectrometry is presented in Table 3.1. 

Analyzer Separation Mass range (Da) Mass resolution (m/Am) Application 

Magnetic sector field equilibr Lorentz force and centrifugal force mv2 n-e-v-B= 2 - direction focusing (lens effect) - separation after m/z (prism effect) 1 500 5 000 TIMS, organic ms, double-focusing sector field ms, tandem ms 

In a commercially available device based on Penning traps - the Fourier transform ion cyclotron resonance (FTICR) mass spectrometer - the ions are constrained spatially or rather ions can be 

---

Rapid scanning mass spectrometers providing unit resolution are routinely used as chroaatographic detectors. Ion separation is accomplished using either a magnetic sector, quadrupole filter or ion trap device. Ions can also be separated by time-of-flight or ion cyclotron resonance mass analyzers but these devices are not widely used with chromatograidiic inlets and will not be discussed here [20]. 

In analyses where molecular masses are being matched, more accurate mass measurements provide more reliable matches and identifications.26,65,66 In a reference laboratory the mass accuracy to several decimal points, provided by a Fourier transform ion cyclotron resonance mass analyzer, may be desirable. In field or portable systems there is usually a trade-off in mass accuracy for size and ruggedness. Reliable identifications can be made with moderate mass accuracy, even 1 Da, if a large enough suite of molecular ions is recorded and used to search the database. If both positive ion and negative ion spectra are... 

There are several instrumental MS methods that can be used to obtain sequence information from proteins and peptides. ESI-triple-quadrupole is frequently used this configuration produces a reasonable number of fragments, the resolution is usually sufficient and the equipment is relatively inexpensive. With this MS/MS configuration, peptides up to 2500 Da can be analyzed. A MALDI with a TOF reflectron and Fourier transform-ion cyclotron resonance mass analyzers are also beginning to be used.21... 

Short-lived reaction intermediates and products resulting fi-om light flash photolysis have been detected using TOF-MS [76]. A flash lamp was used to induce photochemical reactions of the reactant gases in a reaction vessel. The generated species, such as radicals, could be immediately (in approximately milliseconds) detected by TOF-MS [76]. In other work, a laser beam was combined with an ion cyclotron resonance mass analyzer to follow the process of photodissociation [77]. The dissociation rates and branching ratios for naphthalene ion were measured by means of the time-resolved photodissociation approach. The above-mentioned approaches [76,77] are limited to detection of species generated from gas-phase substrates. 

Ion cyclotron resonance (ICR) analyzer A device to determine the mass-to-charge of an ion in a magnetic field by measuring its cyclotron frequency. 

Multiple mass analyzers exist that can perform tandem mass spectrometry. Some use a tandem-in-space configuration, such as the triple quadrupole mass analyzers illustrated (Fig.3.9). Others use a tandem-in-time configuration and include instruments such as ion-traps (ITMS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS or FTMS). A triple quadrupole mass spectrometer can only perform the tandem process once for an isolated precursor ion (e.g., MS/MS), but trapping or tandem-in-time instruments can perform repetitive tandem mass spectrometry (MS ), thus adding n 1 degrees of structural characterization and elucidation. When an ion-trap is combined with HPLC and photodiode array detection, the net result is a profiling tool that is a powerful tool for both metabolite profiling and metabolite identification. 

Ion detection is carried out using image current detection with subsequent Fourier transform of the time-domain signal in the same way as for the Fourier transform ion cyclotron resonance (FTICR) analyzer (see Section 2.2.6). Because frequency can be measured very precisely, high m/z separation can be attained. Here, the axial frequency is measured, since it is independent to the first order on energy and spatial spread of the ions. Since the orbitrap, contrary to the other mass analyzers described, is a recent invention, not many variations of the instrument exist. Apart from Thermo Fischer Scientific s commercial instrument, there is the earlier setup described in References 245 to 247. 

Fourier transform ion cyclotron resonance (FTICR) analyzer is excellent for MSn measurements (see Section 2.2.6), perhaps even more so, since the ions remain in the cell after detection. In principle one injection of ions is enough for a whole MSn sequence, including acquisition of a mass spectrum of each step. 

The mass analyzer separates the molecular ions and fragments according to their mass-to-charge ratios. Common mass analyzers are the quadrupole, ion trap (IT), time-of-flight (TOE), magnetic sector, and ion cyclotron resonance (ICR) analyzers. 

Fig. 6 Schematic of a FTICR MS instrument. This type of MS consists of an ion cyclotron resonance (ICR) analyzer cell that is situated in the homogeneous region of a large magnet. The ions introduced into the ICR analyzer are constrained (trapped) by the magnetic field to move in circular orbits with a specific frequency that corresponds to a specific mass-to-charge ratio (m/z). Mass analysis occurs when radiofrequency (rf) potential is applied (pulsed) to the ICR analyzer so that all ions are accelerated to a larger orbit radius. After the pulse is turned off, the transient image current is acquired and a Fourier transform separates the individual cyclotron frequencies. Repeating this pulsing process to accumulate several transients is used to improve the signal-to-noise ratio. (Courtesy of Bruker Daltonics, Billerica, MA.)...

Preferably, electrospray ionization (ESI) is used in combination with quadrupole mass filters [16,17], whereas MALDI is commonly used in combination with the time-of-flight (TOF) analyzer [18], The relatively simple construction of these two types of analyzers and the resulting price advantage has led to their replacing the traditional magnetic sector instruments as the workhorses of mass spectrometric analysis. A more recent development is the ion-cyclotron-resonance (ICR) analyzer [19] which can be used for both ES-and MALDI-ionization. 

Direct determination of the charge states can also be done by recording the ESI mass spectrum on an instrument that allows for the resolution of the isotope peaks of the analyte. (Chapter 1 in this book discusses mass resolution in greater detail.) Figure 4.4 shows the resolution of isotope peaks, by using ESI and Fourier-transform ion-cyclotron resonance mass spectrometry (FT-ICR) for the multiply charged ion of recombinant human insulin with m/z 1162.53 as a centroid. (The resolving power of the analyzer used to record... 

---