Ionization Device

Note Ultrapure N2 for use in flame-ionization devices may be generated by the Serfass Apparatus available commercially. 

In the sheathless interface, the electrical contact is obtained by coating with either a metal [85, 88-90] or a conductive polymer [91] the separation capillary outlet, which is shaped as sharp tip. Also employed are sheathless interfaces in which the electrical contact is established using a metal electrode or a conductive wire inserted into the outlet of the separation capillary [92], A small gap between the separation capillary and the needle of the ionization device filled by a liquid is the approach made to establish the electrical contact in the liquid junction interface [86,87], This arrangement is also realized by making porous through chemical etching the tip [93] or a small section of the wall [94] of the separation capillary at its outlet. 

Figure 18.4 Schematic illustration of the Townsend avalanche in a gas ionization device. The avalanche occurs very close to the wire in reality. (From Knoll, 2000.)...

The mass spectrometer consists of an inlet system, an ionization device, a mass analyzer, and an ion detector, and the system is kept at a vacuum of about 10 4 to 10 7 Torr. (There are various options available for all four basic components which illustrates the versatility of the technique.) The following describes an electron impact-quadruple mass spectrometer. 

Localized ionization (corona discharges) from sharp, grounded, conducting probes or wires can on occasions be used to reduce the level of electrostatic charge from powder particles entering a vessel. Electrostatic ionization devices are not, however, without problems, and should only be used after consulting expert advice. 

Comi G, Urso R, Paiani M, Ottaviani S (2005a) Dry cured ham cured and packaged in modified atmosphere or under vacuum effects of different additives and of Aw on the behavior of L. monocytogenes. Ind Alim XLIV, Marzo, 272-278 Comi G, Lovo A, Bortolussi N, Paiani M, Berton A, Bustreo G (2005b) Use of an ionizing device for air decontamination in cells used for the production of San Daniele dry cured ham. Ind Alim XLIV, Ottobre, 1-9... 

Figure 16.6 A simplified schematic of a time of flight spectrometer and the principle of the ion reflector (reflectron). (1) sample and sample holder (2) MALDI ionization device by pulsed laser bombardment (3 and (3 ) ions are formed between a repeUer plate and an extraction grid (PD 5000V) then accelerated by an other grid (4) control grid (5) microchannel collector plate (6) signal output. Below, a reflectron, which is essentially an electrostatic mirror that is used to time-focus ions of the same mass but which have initially different energies. The widths of the peaks are of the order of 10 and the resolution ranges between 15 to 20 000.

Ionization device. In a spectrometer, molecules are subjected to ionization because it is easier to control and direct the movement of ionized molecules with an electrical charge than neutral molecules. Usually, the ionization is achieved either by protonation (addition of an H+ ion) or by deprotonation (removal of an H+ ion). These two methods are called positive and negative ionization. Proteins and peptides are usually subjected to positive ionization because the NH2 group in protein readily accepts an... 

The mass analyzer. After the process of ionization, the ionized molecules of proteins or peptides enter the section of the mass spectrometer called the mass analyzer, where they are separated based on their mass-to-charge ratio by electric and/or magnetic fields or by measuring the time taken by an ion to reach a fixed distance from the point of ionization to the detector. Different kinds of analyzers are available for the separation of ionized molecules. Among the different kinds of analyzers, two particular kinds, called the quadrupole and the time-of-flight (TOF) analyzers, are the most important from the point of proteomics for their use in mass spectrometers. A particular spectrometer may use one or the other or at times a combination of both quadupole and TOF analyzers. Usually, the machine with the electrospray ionization device carries a quadrople analyzer. A spectrometer with a MALDI device has a TOF analyzer or a combination of quadrupole and TOF analyzers in succession to each other. Certain spectrometers called tandem spectrometers (MS/MS) contain two or three quadruples and a TOF analyzer. 

Electrospray ionization mass spectrometry (ESI—MS is a tandem technique it employs an electrospray ionization device (ESI) to produce bare ions in the gas phase from a supplied (usually aqueous) solution, and supplies these ions as a very dilute gaseous stream to the high vacuum chamber of a mass spectrometer, which is the analyser. This analyser sorts and detects ions by mass/charge ratio (mlz), as cations or as anions, and will report either on request. For coordination complexes, the ESI process can be sufficiently soft ... 

Over the years, many different approaches based on these two basic principles have been developed.4 9 We decided to focus on developing an approach to transfer analytes by coupling capillary tubing with electrospray ionization devices. From this basic design principle, we were able to develop a simple three-position device for the analysis of proteomic samples by mass spectrometry.7,10 We developed this principle further into an automated nine-position device,6 and to perform frontal analysis separations of peptides.11 This chapter reviews these early developments in coupling microfabricated devices to mass spectrometers. 

Mayeresse, Y, Veillon, R., Sibille, P. H., Nomine, C., 2007. Freeze-drying process monitoring using a cold plasma ionization device. PDA J. Pharm. Sci. Technol. 61 160-174. 

The ESI ion source is amongst the softest ionization devices in which only quasi-molecular ions are generated and in-source CID can be minimized in most of cases. The electrospray ionization process is so soft that even solvent adducts, dimers, and other complexes that normally only exist as weakly bound complexes in solution are observable as distinct ion peaks. 

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