Mass analyser hybrid instruments

In mass spectrometers, ions are analysed according to the ml7. (mass-to-charge) value and not to the mass. While there are many possible combinations of technologies associated with a mass-spectrometry experiment, relatively few forms of mass analysis predominate. They include linear multipoles, such as the quadrupole mass filter, time-of-flight mass spectrometry, ion trapping forms of mass spectrometry, including the quadrupole ion trap and Fourier-transform ion-cyclotron resonance, and sector mass spectrometry. Hybrid instruments intend to combine the strengths of the component analysers. 

Instruments that incorporate two or three mass analysers in a series have been developed to study ion fragmentation. Several of the same type of mass analyser can constitute a tandem mass spectrometer, or they can be constructed using different mass analysers (hybrids). Hybrid spectrometers include the combination of magnetic sector followed by quadrupole, multiple quadrupole, quadrupole TOF, etc. In these instruments, a collision cell is placed between each analyser (Fig. 16.23). Tandem instruments have different scanning modes. 

For some kinds of analyses, it is convenient to have two combined mass spectrometers. This combination naturally increases costs therefore purchase of such hybrid instruments tends to require much... 

Hybrid mass spectrometer An MS-MS instrument combining magnetic sector and quadrupole mass analysers. 

Various tandem MS instrument configurations have been developed, e.g. sector instruments, such as CBCE, CBCECB or CECBCE, and hybrid instruments, e.g. BCECQQ (B = magnetic sector analyser, E = electrostatic analyser, C = collision cell, Q = quadrupole mass spectrometer), all with specific performance. Sector mass spectrometers have been reviewed [168],... 

Mass resolution generally increases for instruments in the listed order. Hybrid variants utilising various composites of mass analysers are likewise available and have become commonplace (e.g. quadrupole-ToF). 

Triple-quadrupole and more recently hybrid instruments, for instance the quadrupole TOF instrument or the ion trap-FT ion cyclotron resonance mass spectrometer, allow one to obtain a mass spectrum resulting from the decomposition of an ion selected in the first analyser. The time-dependent decomposition of a selected ion can also be observed in ion cyclotron resonance and ion trap instruments. They allow fragments over several generations (MS") to be observed. 

Some mass spectrometers combine several types of analysers. The most common ones include two or more of the following analysers electromagnetic with configurations EB or BE, quadrupoles (Q), ion traps (ITs) with Paul ion traps or linear ion traps (LITs), time-of-flight (TOF), ion cyclotron resonance (ICR) or orbitrap (OT). These are named hybrid instruments. The aim of a hybrid instrument is to combine the strengths of each analyser while avoiding the combination of their weaknesses. Thus, better performances are obtained with a hybrid instrument than with isolated analysers. Hybrids are symbolized by combinations of the abbreviations indicated in the order that the ions travel through the analysers. 

An IT analyser has also been coupled to an ICR FTMS instrument, yielding a hybrid instrument in the IT ICR configuration. This hybrid instrument gives high sensitivity at the attomole level, a high resolution of 100000FWHM at 1 s scan rate and a high mass accuracy of 1 to 2 ppm with external calibration at 1 scan per second. A similar hybrid instrument in which the ICR analyser is replaced by an orbitrap analyser has also been... 

Low-energy CID spectra are measured using triple quadrupole, ion trap, ICR or hybrid instruments. For tandem mass spectrometers in space, the collision chamber is most often a quadrupole in the RF mode only, which allows one to focus the ions that are angularly dispersed by the collision. The pressure difference between the collision cell and the rest of the analyser is obtained through differential pumping. 

A TOF mass analyser requires a pulsed ion introduction. In an electrospray-TOF combination, the duty cycle is an important issue. A significant improvement in the duty cycle can be achieved in an ion-trap-TOF hybrid instmment the ions from a continuous ion source are accumulated in the ion trap between two ion introduction events. An ion-trap-TOF hybrid instrument was first described by the group of Lubman [68-69]. The system consists of an atmospheric-pressure ion source with a vacuum interface, a set of Einzel lenses, an ion-trap device, and a reflectron time-of-flight mass analyser. The system was applied for fast analysis in combination with a variety of separation techniques [70]. 

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]. 

The development of hybrid instruments has improved product ion analysis to a great extent in comparison to both QqQ and ion-trap mass analyzers. For example, QqTOF instruments have good mass accuracy and resolving power for determining product ions, whereas QqLIT instruments allow for MS" analysis in addition to NLS and PIS analyses [59]. It should be noted that QqTOF mass spectrometers are incapable of virtual NLS and PIS analyses, but can extract NLS- and PlS-like dataset from the array of product ion analysis data. 

Since the ESI ion source is compatible with nearly all of mass analyzers in which tandem MS can be performed, a variety of types of mass spectrometers are employed for characterization of lipids. Some examples of the instruments that are used to perform tandem MS include tandem sectors, QqQ, ion-trap, ion-cyclotron resonance, TOF/TOF, and hybrid instruments such as Q-TOF. The majority of tandem MS analyses presented in this part are conducted by using the QqQ-type instrument since majority of the early studies on characterization of lipid species were conducted with this type of instrument, and the characterized fragmentation pattern from this type of instrument can well represent those obtained from other types of instruments even including MALDI-MS [4, 5]. 

Fig. 1.38 Example of a hybrid mass analyser instrument. A schematic of standard Q-TOF instrument, which is equipped with quadrupole (Q) and Time of Flight (TOF) mass analysers, thus classified as a Q-TOF. Separating the two mass analysers is a coUision cell for tandem MS...

Two different approaches can be used for EGA. In the most popular approach, two analytical technologies are coupled to form a hybrid instrument and the materials investigated in real time. For example, thermogravimetric analyser coupled to a fourier transform infrared spectrophotometer (TG-FTIR) or thermogravimetric analyser coupled to a mass spectrometer (TG-MS) analysis in which volatilised products that evolve during heating... 

Mass spectrometric analysis was performed with a hybrid triple quadrupole/ linear ion trap Applied Biosystem MSD Sciex 4000QTRAP (Applied Biosystems, Foster City, USA) instrument equipped with a Turbospray ESI interface. For target quantitative analyses, data acquisition was performed in SRM, recording the transitions between the precursor ion and the two most abundant fragment ions. The developed instrumental method display excellent LODs in SRM mode between 0.5 and 1.2 pg (Table 2). 

---