Ion sources electrospray

Yamashita M and Fenn J B 1984 Electrospray ion source. Another variation on the free-jet theme J. Phys. C Solid State Phys. 88 4451... 

ESI and APCI are soft ionisation techniques which usually result in quasi-molecular ions such as [M + H]+ with little or no fragmentation molecular weight information can easily be obtained. However, experimental conditions can also be chosen in such a way that a sufficiently characteristic pattern is obtained, allowing verification [540]. ESI is amenable to thermally labile and nonvolatile molecules. Both ESI and APCI are much more sensitive than PB and very well suited for quantitative analysis, but less so for unknown samples. The choice among the two is usually determined by the application. Recently, nanoscale LC-ESI-MS has been developed [541]. The nano-electrospray ion source offers the highest sensitivity available for LC-MS (atto-to femtomole range) and can also be used as an off-line ion source. 

Hunt, S. M. Sheil, M. M. Belov, M. Derrick, P. J. Probing the effects of cone potential in the electrospray ion source Consequences for the determination of molecular weight distributions of synthetic polymers. Anal. Chem. 1998,70,1812-1822. 

Micromass Quatro II triple stage quadrupole fitted with an electrospray ion source for ESI MS and ESI MS/MS (MRM mode) analysis... 

M. Yamashita and J. B. Fenn. Electrospray Ion Source Another Variation on the Free-Jet Theme. J. Phys. Chem., 88(1984) 4451-4459. 

A. N. Verentchikov, W. Ens, and K. G. Standing. Reflecting Time-of-Flight Mass Spectrometer with an Electrospray Ion Source and Orthogonal Extraction. Anal. Chem., 66(1994) 126-133. 

M. Hardman and A. Makarov. Interfacing the Orbitrap Mass Analyzer to an Electrospray Ion Source. Anal. Chem., 75(2003) 1699-1705. 

The main principles of de novo sequencing will be discussed here using a few d spectra that were acquired using an ion trap mass spectrometer equipped with an electrospray ion source, under low energy collision induced dissociation (CID). 

Fig. 1. Schematics of an electrospray ion trap mass spectrometer. The ions produced from the electrospray ion source are transferred into the vacuum system of the mass spectrometer and guided into the trapping region where they are stored. After storage they can be scanned toward the detector to generate a mass spectrum. Alternatively, ions of a single m/z can be stored inside the trap, accelerated so that they fragment on collision with restgas molecules, and the fragments can be scanned toward the detector to determine their mass.

Triple quadrupole mass spectrometers are combined with electrospray ion sources (Fig. 2). The mass spectrometer has two mass-determining... 

Time-of-flight mass spectrometers are interfaced with MALDI and electrospray ion sources. For proteomic applications they are most often interfaced with MALDI (Fig. 3). All ions from the ion source are accelerated to the same energy and then are left to drift in a field-free region. 

Fig. 11.3. Schematic of an early electrospray ion source. Reproduced from Ref. [2] by permission. American Association for the Advancement of Science, 1989.

Figure 7 Electrospray ion source (From www.astbury.leeds.ac.uk/Facil/Mstut/ mstutorial.htm. With permission from Dr. A. E. Ashcroft, University of Leeds, UK).

Electrospray ion sources display all the characteristics of being concentration dependent. It is therefore normal to split the eluent flow after the UV detector, such that around 300 pl/min goes to the mass spectrometer and the remainder to waste. Care needs to be taken to ensure that there is minimal band broadening caused by the split. It should be possible to minimise band broadening by careful choice of tubing size and positioning of the split point. 

Due to the increasing significance of soft ionization techniques for the analysis of phosphorus-, metal- and metalloid-containing biomolecules, matrix-assisted laser-induced desorption/ionization (MALDI) and electrospray ion sources (ESI) will be discussed briefly at the end of this chapter. 

Electrospray ion source electrospray ioniz., Coulomb repulsion M"+ atmospheric pressure ToF-MS, FTICR-MS tandem MS biomolecules... 

Hardman, M., and Makarov, A. A. (2003). Interfacing the orbitrap mass analyzer to an electrospray ion source. Anal. Chem. 75 1699-1705. 

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