Mass-analyzed ion kinetic-energy spectrometry (MIKES) is a

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is u ...

technique by which mass spectra are obtained from a

sector instrument A sector instrument is a general term for a class of mass spectrometer that uses a static electric (E) or magnetic (B) sector or some combination of the two (separately in space) as a mass analyzer. Popular combinations of these sectors have been ...

that incorporates at least one

magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles ...

sector plus one electric sector in reverse geometry (the beam first enters the magnetic sector). The accelerating

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

''V'', and the

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and t ...

''B'', are set to select the precursor ions of a particular ''m/z''. The precursor ions then dissociate or react in an electric field-free region between the two sectors. The ratio of the

kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its a ...

to charge of the product ions are analyzed by scanning the electric sector field ''E''. The width of the product ion spectrum peaks is related to the kinetic energy release distribution for the dissociation process.

History

MIKES was developed at Purdue University in 1973 by Beynon, Cooks, J. W. Amy, W. E. Baitinger, and T. Y. Ridley."MIKES: History and Significance .ASMS, Web. . MIKES was invented because researches at Purdue and Cornell thought that if the parent ion was mass-selected before the dissociation and mass analysis of the products by the electric sector it would be easier to study the

metastable In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...

ions and the collision-induced dissociation (CID). This was an achievement because it combined the utility of previous instruments such as the ion kinetic energy spectrometer with the ability to mass select precursor ions. That precursor ion is mass selected with the magnetic sector. The dissociation products are then mass analyzed using the electric sector. "The peak shapes revealed from the electric sector scan can provide information on the kinetic energy release from in the course of fragmentation and on the kinetic energy uptake in the course of ionic collision processes." The dispersion of velocities due to kinetic energy release leads to the characteristic wide metastable peaks observed using MIKES techniques.

Application

MIKES is a powerful technique used for structural studies of organic compounds, gaseous ions, and also for direct analysis of complex mixtures without separation of the components. In other words, it is used for

molecular structure Molecular geometry is the three-dimensional arrangement of the atoms that constitute a molecule. It includes the general shape of the molecule as well as bond lengths, bond angles, torsional angles and any other geometrical parameters that deter ...

studies. The reason why MIKES is good for molecular structure studies is due to the reverse-geometry of MIKES. The MIKES Schematic shows that the ion species in the source goes into the magnetic field. After which, the chemistry is later studied in the second field-free region (FFR) by scanning the electric sector which defines the nature of the fragments by measuring their kinetic energy. This causes competitive unimolecular fragmentations that can be observed in the MIKE spectra. Furthermore, if gas is brought into the second FFR, more dissociation will be induced by collision, that will later appear in the MIKE spectra.

Tandem MS scan

This scan uses reverse-geometry (BE-type) instruments. These instruments use a front-end magnetic sector that allows for exclusive mass selection of the precursor ion. The fragmentation region is in-between the two analyzers. The electric sector scan gives the product-ion spectrum. MIKES can also be used for direct measurement of kinetic-energy release values.

Advantages

MIKES, as the name implies, is used for kinetic energy spectrometery. This means that certain criteria are needed to accomplish this. One such feature of MIKES is that it has high kinetic energy resolution and good

angular resolution Angular resolution describes the ability of any image-forming device such as an Optical telescope, optical or radio telescope, a microscope, a camera, or an Human eye, eye, to distinguish small details of an object, thereby making it a major det ...

. This is due to the fact that MIKES has low accelerating voltage, around 3 kilo-volts. Another feature is that it has good differential pumping between the various regions of the instrument. In addition, MIKES has multiple systems for bringing in and/or overseeing collision gases or vapors and the ability to vary slit height and width. This prevents favoritism when determining kinetic energy distributions. Although common now, back in the 1970s, MIKES had a great computer compatibility that allowed for readily obtainable molecular structures.

Disadvantages

A disadvantage to MIKES is that observations are made later in the ion flight path when compared to other methods. Also, a smaller number of ions will typically

decompose Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...

. This will in turn cause the sensitivity to be lower than other kinetic energy spectroscopy methods.

History

Application

Tandem MS scan

Advantages

Disadvantages

See also

References

Further reading