Tandem quadrupole-Fourier transform mass

D. F. Hunt, J. Shabanowitz, R. T. Mclver, Jr., R. L. Hunter, and J. E. P. Syka, "Ionization and Mass Analysis of Nonvolatile Compounds by Particle Bombardment Tandem-Quadrupole Fourier Transform Mass Spectrometry," Anal. Chem., 57, 765-768 (1985). 

Laser-microprobe mass spectrometers are used for the study of solid surfaces. Ablation of the surface is accomplished with a high-power, pulsed laser, usually a Nd-YAG laser. After frequency quadrupling, theNd-YAG laser can produce 266-nm radiation focused to a spot as small as 0.5 pm. The power density of the radiation within this spot can be as high as 10to 10" W/cm. On ablation of the surface a small fraction of the atoms are ionized. The ions produced are accel crated and then analyzed, usually by tlme-of-flight mass spectrometry. In some cases laser microprobes have been combined with quadrupole ion traps and with Fourier transform mass spectrometers. Laser-microprobe tandem mass spectrometry is also receiv-... 

It should be pointed out that FAB, MALDI, and ESI can be used to provide ions for peptide mass maps or for microsequencing and that any kind of ion analyzer can support searches based only on molecular masses. Fragment or sequence ions are provided by instruments that can both select precursor ions and record their fragmentation. Such mass spectrometers include ion traps, Fourier transform ion cyclotron resonance, tandem quadrupole, tandem magnetic sector, several configurations of time-of-flight (TOF) analyzers, and hybrid systems such as quadrupole-TOF and ion trap-TOF analyzers. 

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. 

The most common types of MS/MS instruments available to researchers in food chemistry include triple quadrupole mass spectrometers and ion traps. Less common but commercially produced tandem mass spectrometers include magnetic sector instruments, Fourier transform ion cyclotron resonance (FTICR) mass spectrometers, and quadrupole time-of-flight (QTOF) hybrid instruments (Table A.3A.1). Beginning in 2001, TOF-TOF tandem mass spectrometers became available from instrument manufacturers. These instruments have the potential to deliver high-resolution tandem mass spectra with high speed and should be compatible with the chip-based chromatography systems now under development. 

The types of tandem mass spectrometers capable of performing MS/MS experiments fall into two basic categories tandem in space and tandem in time. Tandem-in-space instruments have discrete mass analyzers for each stage of mass spectrometry examples include multisector, triple-quadru-pole, and hybrid instruments (instruments having mixed types of analyzers such as a magnetic sector and a quadrupole). Tandem-in-time instruments have only one mass analyzer where each stage of mass spectrometry takes place in the same analyzer but is separated in time via a sequence of events. Examples of this type of instrument include Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers and quadrupole ion traps, described in Chapter 3. 

Tandcm-in-Time Spectrometers. Tandem-in-iime instruments form the ions in a certain spatial region and then at a later lime expel the unwanted ions and leave the selected ions to be dissociated and mass analyzed in the same spatial region. This process can be repeated many limes over to perform not only MS/MS experiments, but also MS/MS/MS and MS" experiments. Fourier transform ICR and quadrupole ion-trap instruments are well suited lor performing MS" cxperimenls. In principle, tandem-in-time spectrometers can perform M.S/MS experiments much more simply than tandem-in-space instruments because of the dilTiculty in providing different ion focal positions in the latter. Although tandem-in-time spectrometers can readily provide product ion scans, other scans, such as precursor ion scans and neui ral loss scans, are much more difficult to perform than they arc with tandem in space instruments. 

Various forms of tandem mass spectroscopy (MS/MS) have also been used in the analysis of biomolecules. Such instruments consist of an ionisation source (ESI or MALDI or other) attached to a first mass analyser followed by a gas-phase collision cell. This collison cell further fragments the selected ions and feeds these ions to a second mass detector. The final mass spectrum represents a ladder of fragment ions. In the case of peptides the collision cell usually cleaves the peptides at the amide bond. The ladder of resulting peptides reveals the sequence directly [496]. Thus, tandem MS instruments, such as the triple quadrupole and ion-trap instruments have been routinely applied in LC-MS/MS or ESI-MS/MS for peptide sequencing and protein identification via database searching. New configurations, which have been moving into this area include the hybrid Q-TOF [498], the MALDI-TOF-TOF [499] and the Fourier transform ion cyclotron resonance instruments [500]. 

IM has been coupled with a range of mass spectrometers. Both electrospray ionization (ESI) [21,22], and matrix-assisted laser desorption/ionization (MALDI) [18] ionization sources have been used to generate ions prior to IM analysis. Different configurations of mass analyzers have been used to perform mass analysis including quadrupole mass analyzers [23], time-of-flight (TOE) analyzers [24] and Fourier transform ion cyclotron resonance spectrometry (FT-ICR) [25]. Recently, an instrument utilizing two and three drift cells in tandem has been described [26]. 

A variety of mass analyzers have been used in MSI experiments such as TOP, quadrupole ion trap (QIT), linear ion trap (LIT), QqQ, Fourier transform ion cyclotron resonance (FTICR), and Orbitrap. Also, various tandem configurations of these mass analyzers such as QqTOF, QqLIT, and TOF/TOF have been used. Due to the many possible interferenees from endogenous compounds or from the matrix, the use of tandem mass speetrometry (MS/MS or MS") or the ability to perform high-resolution and aeeurate mass measurements for the analysis of drugs by MALDI is essential. An overview of some of the established instrumentation and their respeetive eapabilities is presented below. 

Recently introduced tandem mass spectrometers, having both features, such as quad-rupole linear ion trap (QqLIT, LTQ or Q-trap), quadrupole time-of-fiight (QqTOF), LTQ-Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), and LTQ-Orbitrap, and so on, have allowed for the development of several new methods for acrylamide detection [107,108]. 

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