Matrix‐dependent cationization in MALDI mass spectrometry

Abstract

The matrix dependence in cationization processes, the competition between cationization and protonation and the question of whether gas-phase cation transfer or attachment of free cations dominates in matrix-assisted laser desorption/ionization mass spectrometry were studied. Two different sample preparation methods were employed, the dried-droplet sample preparation and a mixture of solid matrix, analyte and salt. The latter ensures that the formation of cation adducts takes place in the gas phase. By monitoring the suppression of matrix signals for different matrices, it was found that matrices with high gas-phase metal ion binding energies require high analyte concentrations for matrix suppression to occur. By comparing the mass spectra obtained using sinapinic acid or sinapinic methyl ester as a matrix, a correlation between cationization and deprotonation of matrix molecules was found. It is also demonstrated that attachment of free gas-phase cations, rather than cation transfer from the cationized matrix, is the predominant process in cationization.

Biomedical application of MALDI mass spectrometry for small‐molecule analysis

“…We propose that, for porphyrins, the cationized matrix might well be the cation donator to the analytes, whereas analyte cationization with other matrices seems to occur predominantly through attachment of free cations in the gas phase (Zhang & Zenobi, 2004). Ab initio calculations showed that Li þ is attached to the porphyrin cavity and not to the F atoms of the C 6 F 5 groups.…”

Sodium Cation Affinities of Commonly Used MALDI Matrices Determined by Guided Ion Beam Tandem Mass Spectrometry

“…Cationization by alkali metal cations such as Na + and K + is one of the secondary ionization processes that occur in MALDI [25][26][27][28][29][30][31][32][33]. Cationization is also believed to influence protonation, deprotonation, and electron transfer ionization processes that occur in MALDI.…”

On-line matrix addition for detecting aerosol particles

“…4(a), but without PA present in the spectrum. The most intense peaks result from alkalimetal sodium ions Na + and kalium K + , Salt impurities that may originate from the matrix, the analyte, solvents, glassware and from the surface of the sample carrier [14] . The results suggested that uncoated coumarin particles cannot be directly ionized under this experimental condition.…”