Matrix-assisted particle-desorption techniques

Since then, many novel methods have been developed to analyze gene expression and mutation by using electrochemical techniques [1,2], matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MASS) [3], polymerase chain reaction (PCR) [4,5], bacterial magnetic particles [6], and microbeads [7]. 

An ideal interface should not cause extra-column peak broadening. Historical interfaces include the moving belt and the thermospray. Common interfaces are electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCl). Several special interfaces include the particle beam—a pioneering technique that is still used because it is the only one that can provide electron ionization mass spectra. Others are continuous fiow fast atom bombardment (CF-FAB), atmospheric pressure photon ionization (APPI), and matrix-assisted laser desorption ionization (M ALDl). The two most common interfaces, ESI and APCI, were discovered in the late 1980s and involve an atmospheric pressure ionization (API) step. Both are soft ionization techniques that cause little or no fragmentation hence a fingerprint for qualitative identification is usually not apparent. 

Earlier methods of ionization applied to carotenoids, including electron impact (El), chemical ionization (Cl), a particle beam interface with El or Cl, and continuous-flow fast atom bombardment (CF-FAB), have been comprehensively reviewed elsewhere (van Breemen, 1996, 1997 Pajkovic and van Breemen, 2005). These techniques have generally been replaced by softer ionization techniques like electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and more recently atmospheric pressure photoionization (APPI). It should be noted that ESI, APCI, and APPI can be used as ionization methods with a direct infusion of an analyte in solution (i.e. not interfaced with an HPLC system), or as the interface between the HPEC and the MS. In contrast, matrix-assisted laser desorption ionization (MALDI) cannot be used directly with HPEC. 

Mass spectrometry is one physical technique that does not (at least directly) involve electromagnetic radiation. However, some sample desorption and ionization processes do use high intensity pulses of laser light in techniques such as MALDI (Matrix-Assisted Laser Desorption Ionization) that have proved very useful in mass analysis of proteins and other biologic macromolecules. High resolution mass spectrometry derives from atomic/molecular beam studies in which the trajectories of ionized particles in a vacuum can be manipulated by static... 

Numerous ionization techniques have been reported in the last century, which are applicable to modern mass spectrometry. Depending on the method of analyte introduction (e.g., direct inlet, GC, LC, or capillary electrophoresis different strategies have been employed including El, Cl, thermospray, particle beam, electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), fast-atom bombardment (FAB), matrix-assisted laser desorption ionization (MALDI), etc. In sports drug testing, only selected approaches have been applied to routine doping control analyses, which are outlined in the following. 

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