Kinetic-energy-to-charge ratio

Ion kinetic energy spectrum. A spectrum obtained when a beam of ions is separated according to the translational energy-to-charge ratios of the ionic species contained within it. A radial electric field achieves separation of the various ionic species in this way. 

The magnetic sector creates a dispersion of ions according to their momentum-to-charge ratios, while the radial electric sector disperses them according to their ratios of kinetic energy-to-charge. In a one-dimensional model these results yield the following set of equations ... 

Neutrons readily induce nuclear reactions, but they always produce nuclides on the high neutron-proton side of the belt of stability. Protons must be added to the nucleus to produce an unstable nuclide with a low neutron-proton ratio. Because protons have positive charges, this means that the bombarding particle must have a positive charge. Nuclear reactions with positively charged particles require projectile particles that possess enough kinetic energy to overcome the electrical repulsion between two positive particles. 

The mass-to-charge ratio, m/n, of those ions that pass through the probe aperture and are analysed in the mass spectrometer is calculated from the equivalence between the potential energy of the atom on the specimen surface at voltage V0, and the kinetic energy that the atom acquires during acceleration to the grounded... 

Time of flight analyzers use an electric field to accelerate ions to the same kinetic energy and then measure the time it takes for the ions to reach the detector. The velocity of the ions, and thus the time of flight to the detector, depends only on the mass-to-charge ratio... 

Mass-to-charge ratios are determined by measuring the time that ions take to move through a field-free region between the source and the detector. Indeed, before it leaves the source, an ion with mass m and total charge / = zc is accelerated by a potential Vs. It electric potential energy Eei is converted into kinetic energy / / ... 

The trapped ions possess characteristic oscillation frequencies. The stable motion of ions in the trap is assisted by the presence of a helium buffer gas (1 mtorr) to remove kinetic energies from ions by collisions. When a supplementary AC potential, corresponding to the frequency of a certain m/z ion, is applied to the end-cap electrode, ions are resonantly ejected from the trap. This method of resonance ejection is used to effectively extend the mass-to-charge ratio of the ion trap. Some other characteristic features of a 3-D ion trap include high sensitivity, high resolution with slow scan rate, and multiple-stage MS capability (see the section on tandem MS). In addition, it is inexpensive and small in size. As a result, a 3-D ion trap is widely used in LC/MS and LC/MS/MS applications. 

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