Fourier-transform Mass Analyzers

Fourier-transform (FT) mass analyzers belong to a special class of mass analyzer that detects ions non-destructively and periodically. Therefore, FT mass analyzers are trapping-type instruments. Because periodic and long detection times facilitate accurate ion recognition, FT mass analyzers offer the highest mass resolving power and accuracy of all instruments [23]. The concept of FT-MS was first described by Comisarow and Marshall in the 1970s [24]. The most important types of FT instruments available in the market include ion cyclotron resonance (ICR) [23] and orbital ion trap (orbitrap) [25] mass analyzers. 

Under typical operating conditions, a time-domain signal of hundreds of milliseconds to tens of seconds is necessary to produce a mass spectrum. The long SAT of FT mass 

Dividing by In results in the cyclotron frequency (/c) of this motion  

For a singly charged molecule with a molecular weight of 100 u, moving inside a 7 T magnet,/c can be calculated using Equation 3.34 q in coulombs B in teslas m in kilograms)  

Equation 3.33. Thus, when the RF frequency is in resonance with the ICR frequency of the ion, excitation will bring ions into orbits with large radii based on the relationship [23]  

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Connect to http //chemistry.brookscole.com/skoogfac/. From the Chapter Resources menu, choose Web Works and locate the Chapter 32 section. Find the link to LC-GC magazine. From the LC-GC home page, search for articles on LC/MS. Find an article, written in 2001, that compares mass analyzers for LC/MS applications. What are the most common ionization sources used for LC/MS Describe any differences in mass range and mass resolution between quadrupole, time-of-flight, and ion-trap (Fourier transform) mass analyzers. Do these three mass analyzers show any differences in qualitative and quantitative analysis ... 

D. Ion Cyclotron Resonance and Fourier Transform Mass Analyzers... 

Choi BK, Hercules DM, Zhang T, Gusev AI. 2001. Comparison of quadruple time of flight and Fourier Transform mass analyzers for LC-MS. LC GC 19 514—520. 

Fourier transform mass spectrometry is made possible by the measurement of an AC current produced from the movement of ions within a magnetic field under ultra-high vacuum, commonly referred to as ion cyclotron motion.21 Ion motion, or the frequency of each ion, is recorded to the precision of one thousandth of a Hertz and may last for several seconds, depending on the vacuum conditions. Waveform motion recorded by the mass analyzer is subjected to a Fourier transform to extract ion frequencies that yield the corresponding mass to charge ratios. To a first approximation, motion of a single ion in a magnetic field can be defined by the equation... 

M ass Spectrometry. Field desorption mass spectrometry has been used to analyze PPO (179). Average molecular weight parameters (M and Mj could be determined using either protonated (MH + ) or cation attachment (MNa+) ions. Good agreement was found between fdms and data supplied by the manufacturer, usually less than 5% difference in all cases up to about 3000 amu. Laser desorption Fourier transform mass spectrometry was used to measure PPG ion and it was claimed that ions up to m/z 9700 (PEG) can be analyzed by this method (180). 

Time-of-flight (TOF) MS detectors (Fig. 15.7) are commonly used in pro-teomics studies of proteins and protein fragments because this type of detector can handle and analyze very large molecular and fragmentation ions. Fourier transform mass spectrometers (FTMS) are being incorporated into commercial LC/MS systems and offer the advantage of being nondestructive detectors that can trap and repeatedly analyze the same sample in order... 

All experiments were performed using a Nicolet Analytical Instruments FTMS-2000 dual-cell Fourier transform mass spectrometer with optional GC and laser desorption interfaces. The FTMS-2000 dual cell is specially constructed of stainless steel with low magnetic susceptibility. This permits very efficient ion transfer between the source and analyzer cells, if the cells are properly aligned in the magnetic field. 

Trypsin digests of both wild type HRV virus and the mutant were analyzed using MALDI-TOF and MALDI Fourier transform mass spectrometry (FTMS). For HRV, the mass spectra for both wild-type and mutant were identical except for one peptide occurring at mlz 4700. This corresponds to residues 187-227 in the wild type sequence. The corresponding peak in the mutant mass spectrum occurs at 4783.5 (Fig. 4, inset). This mass difference of 83 Da corresponds exactly to a mutation of a Cys to Trp residue and there are no other possible mutations that would be separated by 83 Da. Since there is only one Cys in the peptide 187-227 at position 199, the mutant can be localized as HRV14-Cysl99Trp, which contains a Trp at position 199 instead of Cys in the wild type. 

The first step is the priming of the NRPS active site and a subsequent limited tryptic digest of the protein. The digested sample is loaded on a reverse-phase liquid chromatography (RPLC) C18 column, which is directly connected to the inlet of an FT mass spectrometer. During online LC separation, the eluent is analyzed by MS and MS2 on an LC timescale. In the mass spectrometer the eluent is first analyzed by broadband Fourier transform mass spectrometry (FTMS). Then, peaks in the resulting broadband FT mass spectrum are... 

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. 

A number of mass analyzers in use today have been coupled to these sources. These include two- and three-dimensional quadrupole field, time-of-flight (TOF), quadrupole-TOF hybrids, magnetic sector, and Fourier transform mass spectrometers. Paramount to the mass spectrometer analyzer used in the analysis is proper sample preparation. With proper preparation of proteins and peptides, their molecular weights can be determined with high mass accuracy. Conversely, a poorly prepared sample will lead to poor or no mass spectrometer results. For peptides and proteins, the mass accuracy is typically better than 0.01%. 

Along with advances in various ionization sources, significant improvements have been made in the area of mass analyzers. Mass analyzers can be differentiated based on several attributes such as scan speed, duty cycle, mass resolution, mass range, and cost [126], The most common analyzers used for metabonomics analyses include the quadrupole and TOF-based analyzers [125-127], Some other analyzers that have been reported for use in MS-based metabonomics analyses are the ion traps, Orbitraps, and Fourier transform mass spectrometers [128,129],... 

Other Mass Analyzers. Other analyzers, such as quadrupole ion trap (QIP) and Fourier transform mass spectrometer (FTMS), are of some interest for proteomics. The quadrupole ion trap mass analyzer was devised by Wolfgang Paul it works on the principle of trapping ions with a particular RF in the quadrupole mass analyzer. This device provides a way to eject ions of certain radio frequency and retain the others, only the latter are allowed to reach the detector by scanning ions of a particular radio frequency. In this method, the selected ions can be subjected to fragmentation by collision-induced dissociation (CID), which is useful for the analysis of peptides. 

Burnt gas composition using either dedicated single-species analyzers or multicomponent methods such as Fourier transform infrared analyzer (FTIR) and mass spectrometer (MS) and... 

For infrared laser desorption Fourier transform mass spectrometry (LD-FTMS), all den-drimer samples were prepared by dissolving ca. 1 mg of sample in CH2CI2, followed by deposition upon stainless steel probe tips by the aerosol spray technique described previously [37]. Dendrimer samples 4 and 5 were deposited directly onto a stainless steel probe tip. The sample 6 was prepared by first spraying 50 mL of a saturated silver nitrate/ethanol solution (containing ca. 3 mg of silver nitrate) onto the rotating probe tip, prior to dendrimer deposition. Samples were introduced into the vacuum system and the source cell pressure reduced to 2.2 X 10 Torr and the analyzer cell pressure to 2.0 x 10 Torr, before analysis. 

In virtually all types of experiments in which a response is analyzed as a function of frequency (e.g., a spectrum), transform techniques can significantly improve data acquisition and/or data reduction. Research-level nuclear magnetic resonance and infra-red spectra are already obtained almost exclusively by Fourier transform methods, because Fourier transform NMR and IR spectrometers have been commercially available since the late 1960 s. Similar transform techniques are equally valuable (but less well-known) for a wide range of other chemical applications for which commercial instruments are only now becoming available for example, the first commercial Fourier transform mass spectrometer was introduced this year (1981) by Nicolet Instrument Corporation. The purpose of this volume is to acquaint practicing chemists with the basis, advantages, and applications of Fourier, Hadamard, and Hilbert transforms in chemistry. For almost all chapters, the author is the investigator who was the first to apply such methods in that field. 

Fourier transform (FT) analyzers. The FT instruments have the highest available resolution. Currently there are two types, the orbitraps and the ion cyclotron resonance (ICR) systans. Mass resolution in orbitraps can reach 250,000, while ICR systems can have resolutions of >3,000,000. In these analyzers ions oscillate/rotate within a cell and are detected by recording the electrical current that the passage of ions induces in the snrfaces of the cell. The resolution attainable is inversely proportional to both the mass of the analyte ion and the time required to acquire the data. A consequence of this proportionality is that the highest resolutions cannot be obtained on the chromatographic timescale where mnltiple spectra must be collected to enable the characterization of peaks that are only a few seconds wide. LIT/FT combinations are the most common form of MS/MS systems that ntilize orbitrap and ICR analyzers (Sections 2.3.4 and 23122). 

While most mass analyzers such as quadmpole, ion trap, or TOF require destructive detectors such as electron multiplers or multichannel plate detectors, in Fourier transform mass spectrometry (FTMS) the detector uses a nondestructive detection mode. Ion cyclotron resonance (ICR) and the orbi-trap uses Fourier transform detection. 

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