Kinetic energy discrimination

A number of optical photoion-photoelectron coincidence experiments have been reported107 giving qualitative information on molecular breakdown. However, in these experiments little or no attempt has been made to correct for either the transmission efficiency of the photoelectron spectrometer or the ion kinetic-energy discrimination. Fragment ions usually... 

Overcoming Spectral Interference via Collisional Deceleration and Kinetic Energy Discrimination... 

K. (2002) The effects of cell-gas impurities and kinetic energy discrimination in an octopole collision cell ICP-MS under non-thermalized conditions. J. Anal. At. Spectrom., 17, 213-1222. 

Collision mechanisms using nonreactive gases and kinetic energy discrimination (KED)... 

FIGURE 10.2 Principles of kinetic energy discrimination (courtesy of Thermo Scientific). 

It is also worth explaining point number 7 above in greater detail because it is not a classical contamination issue. In a collision cell that uses kinetic energy discrimination (KED) to suppress the polyatomic interference, the cell relies on interactions of the interfering ion with an inert or low-reactivity gas, such that it can be separated from the analyte based on their differences in kinetic energy. If the gas contains impurities such as H2O, O2, CO2, CO, or hydrocarbons, the impurity could be the dominant reaction pathway as opposed to the predicted collision/reaction with bulk gas, resulting in the formation of additional and unexpected spectral interferences. 

Because of the disparity of the reaction rates of the two neutralization reactions, the analyte can be efficiently determined after the introduction of ammonia as a reactive gas into the multipole. There are many excellent reviews about the development and applications of collision/reaction cell in ICP-MS. " In order to eliminate the new isobaric interferences produced by secondary reactions, two methods are commonly used in the commercial instrument the discrimination of kinetic energy or mass filtering. " The former mainly utilizes the post-cell kinetic energy discrimination (KED) to suppress transport of the produces of the side reactions to the analyte in the hexapole and octapole cell instruments. Whereas in the latter, the quadrupole cell has a capability to reduce the formation of the unwanted side product ions by selecting an appropriate mass bandpass. The details of the KED and bandpass approaches can refer to many excellent books and reviews. " " ... 

Another suprathermal process that is used for suppression of unwanted ions is kinetic energy discrimination (KED). It was first used by Rowan and Houk to prevent polyatomic ions formed in-cell from entering the analyzer, by providing a potential energy barrier between the cell and the analyzer. Ions formed in the cell originate at a potential that is close to the cell rod bias (I CRo) and have little residual kinetic energy (which may be acquired from the precursor ion). 

Anicich, V. G. (2003) An index of the literature for bimolecular gas phase cation-molecule reaction kinetics. JPL Publication, Jet Propulsion Laboratory, Pasadena, CA, pp. 03-19. Yamada, N., Takahashi, J., and Sakata, K. (2002) The effect of cell-gas impurities and kinetic energy discrimination in an octopole collision cell ICP-MS under non-thermalised conditions. J. Anal. At. Spectrom., 17,1213-22. 

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