Ultraviolet MALDI methods

Gluckmann, M. Karas, M. The Initial Ion Velocity and Its Dependence on Matrix, Analyte and Preparation Method in Ultraviolet MALDI. J. Mass Spectrom. 1999, 34,461 All. 

FIGURE 15.2 Common protein ionization methods used for MS-based proteomics. Two common ionization technologies are currently available for protein analysis. Top ESI volatilizes and ionizes peptides and proteins in solution. Bottom MALDI uses analytes that are co-crystallized in a matrix composed of organic acid on a solid support. A pulse of ultraviolet laser evaporates the matrix and analyte into gas phase, resulting in generation of single charge ions. 

Major methods for introducing proteins and other macromolecules into mass spectrometers are electrospray and matrix-assisted laser desorption/ionization (MALDI).18-27 Most often, MALDI is used with a time-of-flight mass spectrometer, which can measure mlz up to 106. Typically, 1 p,L of a 10 jxM solution of analyte is mixed with 1 p,L of a 1-100 mM solution of an ultraviolet-absorbing compound such as 2,5-dihydroxybenzoic acid (the matrix) directly on a probe that fits into the source of the spectrometer. Evaporation of the liquid leaves an intimate mixture of fine crystals of matrix plus analyte. 

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