Matrix ionization

Little JL, Wempe MF, Buchanan CM (2006) Liquid chromatography-mass spectrometry/mass spectrometry method development for drug metabolism studies examining lipid matrix ionization effects in plasma. J Chromatogr B 833 219-230... 

Only a small portion of secondary particles ( 1 % of total secondary particles) are ionized and become the secondary ions that are analyzed in SIMS. A sputtered particle faces competition between ionization and neutralization processes when it escapes a sample surface. Ionization probability represents the chance of a sputtered particle being an ion. The ionization probability is strongly affected by the electronic properties of the sample matrix. Ionization directly affects the signal intensity of secondary ions as shown in the basic equation of secondary ion yield. 

Technique Analyte Class/ Compound Identified Materials [Reference] Sample Matrix Ionization Mode MS System... 

Another example is the matrix ionization chamber system (vanHerk, 1991 1992). The ionization chamber consists of two printed boards which enclose a thin liquid film. Each plate carries a system of 256 parallel conducting strips. The principle is shown in Figure 8. The strips of one plate are connected to 256 charge-sensitive amplifiers. Voltage pulses are applied successively by a multiplexer to the 256 strips of the other plate. This way, 256 x 256 = 65,536 crossing points exist which function as mini-ionization chambers. The sensitive volume is irradiated continuously by X-rays and the ionization produced in each minichamber is read out. Such a device has been applied as a portal imaging device in radiation therapy (Meertens et al., 1990). 

Solvent-free separation is especially powerful in parmership with solvent-free ion-ization.( Here we discuss a few milestones critically influencing the production of ions of the entire sample to be separated and mass detected. We demonstrated that solvent-free and matrix-ionized laser/desorption (MILD) meth-... 

Trimpin, S. Clemmer, D. E. McEwen, C. N. Charge-remote fragmentation of lithi-ated fatty acids on a TOE-TOE instmment nsing matrix-ionization. J. Am. Soc. Mass Spectrom. 2007,18, 1967-1972. 

Matrix ionization potentials are mostly over 775 kJ/mol. Electron affinities are much lower, lOOkJ/mol or less. Proton affinities range from 850 to more than 900kJ/mol (mH m H ). Electrostatic interactions make the acidities much higher, around 1300kJ/mol(m (m —H) + H ). Radical cation acidities (m (m —H) + H ) are, like the proton affinities, about 850kJ/mol. 

Knochenmuss, R. Vertbs, A. lime-delayed 2-pulse studies of MALDI matrix ionization mechanisms. J. Phys. Chem. B. 2000,104, 5406 5410. 

MALDI ionization is the least understood of the three largely becanse the ionization mechanism is a combination of both a surface ionization process and gas-phase reactions in the ablation plume. Components of the sample that inhibit the formation of crystals decrease the energy transfer at the surface and reduce the ionization efficiency. Reactions of ions and neutrals in the gas phase will also determine the final ion population, similar to APCI. At this point, it is important to distinguish endogenous sample matrix from MALDI ionization matrix. Ionization matrix is the material used to form the crystals that absorb and transfer the photon energy. Endogenous sample matrix is the biological material in a sample. 

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