How, using electrical or electronic means can I subject a mass M of matter to an energy of N electron volts.
(So I want a quantifiable and calculable answer like "for 1 g of Nickel, run a current of X amps under Y volts) or put it in a 1000 watt µ-wave oven.
The ionization source: it consists of vaporizing the molecules and ionizing them. An ionization source can be used either in positive mode to study positive ions, or in negative mode to study negative ions. Several types of sources exist and are used depending on the desired result and the molecules analyzed.
Electronic ionization (EI), chemical ionization (CI) and chemical desorption-ionization (DCI)
The bombardment by fast atoms (FAB), metastable atoms (MAB) or ions (SIMS, LSIMS)
Inductive plasma coupling (ICP)
Chemical ionization at atmospheric pressure (APCI) and photoionization at atmospheric pressure (APPI)
Electrospray or electrospray (ESI)
Desorption-ionization laser assisted by matrix (MALDI), activated by a surface (SELDI) or on silicon (DIOS)
Ionization-desorption by interaction with metastable species (DART)
The electron-volt is a unit of energy, like the Watt-hour or the Joule.elephant wrote:How, [...] then can I subject a mass M of matter to an energy of N electron volts.
The ionization source
The EI and CI ionizations, which require a certain level of vacuum, are preferably used in conjunction with gas chromatography (the CI operating from an EI source). On the other hand, the two sources at atmospheric pressure (electrospray and APCI) called “soft ionization”, are mainly used in coupling with liquid phase chromatography.
Electronic ionization (EI)
Electronic ionization source
Electrons emitted by a filament meet the molecules that enter the source: during the encounter, if the kinetic energy of the electrons is sufficient, an electron is torn from the molecule M, transforming it into a radical ion M + o. This can then fragment according to its internal energy. The IE thus leads to a fairly full spectrum, with many fragments, very rich in structural information.
Chemical ionization (CI) [edit]
Source of chemical ionization
In addition to the above EI device, a reactive gas is introduced into the source and ionized by electronic impact. This is followed by a series of reactions which give rise to ions which can react with the analyte molecules arriving in the source. This type of ion-molecule reaction mainly produces (in positive mode) ions [MH] +, and [M + adduct + H] +, thus allowing access to the molecular mass of the analyte.
Methane, isobutane and ammonia are among the most used chemical ionization gases.
For the detection of globally electronegative molecules, comprising halogenated parts, negative chemical ionization can be used. The principle is to negatively charge these molecules by bombarding them with electrons which will be captured by the electron-withdrawing atoms. Due to the high probability of electron capture, this type of ionization can be 1000 times more sensitive than positive chemical ionization1
Fast atom bombardment ionization (FAB)
It makes it possible to analyze molecules that cannot be vaporized under vacuum (large biological molecules). Ionization is carried out by vapor phase expulsion of the ions contained in a liquid sample following a bombardment of fast atoms (Ar or Xe). The molecules thus ionized do not have much internal energy, the fragmentation is therefore weak but the molecular ion is easily recognizable and the molecular mass is easy to determine. The sample is mixed in solution with a non-volatile liquid matrix (glycerol, thioglycerin, m-nitrobenzyl alcohol). A high energy beam (of the order of 4 to 10 keV) of neutral atoms (Ar or Xe) is sent to the sample and the matrix in the collision chamber thus causing the phenomena of desorption and ionization. Pre-existing ions in solution are expelled in the gas phase and accelerated to the analyzer.
Electrospray ionization (electrospray) (ESI)
Main article: Ionization by electrospray (ESI).
Electrospray ion source
Its principle is as follows: at atmospheric pressure, the droplets of solutes are formed at the end of a fine capillary brought to a high potential. The intense electric field gives them a high charge density. Under the effect of this field and thanks to the possible assistance of a co-axial air stream, the liquid effluent is transformed into a cloud of fine droplets (spray) charged according to the ionization mode. Under the effect of a second stream of heated air, the droplets gradually evaporate. As their charge density becomes too high, the droplets explode, releasing microdroplets made up of protonated or deprotonated molecules of the analyte, carrying a variable number of charges.
The ions thus formed are then guided with the aid of electrical potentials applied to two successive sampling cones acting as barriers with the downstream parts maintained under a high vacuum (<10-5 Torr). During this high pressure journey, the ions undergo multiple collisions with the gas and solvent molecules, which completes their desolvation. By varying the electrical potentials applied in the source, it is possible to cause more or less significant fragmentations.
The advantage of this ionization method as for the APCI is the obtaining of multicharged ions, for the macromolecules, polymers. It also makes it possible to generate a "soft" ionization: the majority of molecular ions are formed.
Chemical ionization at atmospheric pressure (APCI)
Main article: Chemical ionization at atmospheric pressure (APCI).
The liquid samples are directly introduced into a pneumatic nebulizer. Under the effect of a jet of air or nitrogen, the liquid is transformed into a fine mist. Heating ensures the desolvation of the compounds. These are then chemically ionized at atmospheric pressure: in general, the vaporized mobile phase acts as an ionization gas and the electrons are obtained from corona electrode discharges. The ionization of the compounds is very favored during these techniques because the frequency of collisions is high at atmospheric pressure.
APCI is a technique analogous to chemical ionization (CI), it calls for ion-molecule reactions in the gas phase, but at atmospheric pressure and essentially leads to the formation of [MH] + or [MH] ions. -.
Matrix-assisted laser desorption-ionization (MALDI)
Main article: Desorption-ionization laser assisted by matrix.
MALDI ion source
A pulsed laser beam is used, generally in the ultraviolet field, to desorb and ionize a matrix / co-crystallized sample mixture on a metal surface, the target.
The matrix molecules absorb the energy transmitted by the laser in the form of UV photons, excite and ionize. The energy absorbed by the matrix causes its dissociation and its passage into the gas phase. The ionized matrix molecules transfer their charge to the sample. The expansion of the matrix drives the sample into the dense gas phase where it will finish ionizing.
The ionization of the sample therefore takes place either in the solid phase before the desorption, or by charge transfer during collisions with the excited matrix after desorption. It leads to the formation of single-charged and multi-charged ions of the [M + nH] n + type, with a clear preponderance for the single-charged.
What is this very short distance?
Be careful, we would be in an atmosphere of pure hydrogen
)Go back to "Innovations, inventions, patents and ideas for sustainable development"
Users browsing this forum : No registered users and 87 guests
