Premium
Generation of gas‐phase ions from charged clusters: an important ionization step causing suppression of matrix and analyte ions in matrix‐assisted laser desorption/ionization mass spectrometry
Author(s) -
Lou Xianwen,
Dongen Joost L.J.,
Milroy LechGustav,
Meijer E.W.
Publication year - 2016
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7741
Subject(s) - chemistry , analyte , analytical chemistry (journal) , mass spectrometry , ion suppression in liquid chromatography–mass spectrometry , matrix (chemical analysis) , ion , ionization , desorption , matrix assisted laser desorption/ionization , chromatography , organic chemistry , liquid chromatography–mass spectrometry , adsorption
Rationale Ionization in matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) is a very complicated process. It has been reported that quaternary ammonium salts show extremely strong matrix and analyte suppression effects which cannot satisfactorily be explained by charge transfer reactions. Further investigation of the reasons causing these effects can be useful to improve our understanding of the MALDI process. Methods The dried‐droplet and modified thin‐layer methods were used as sample preparation methods. In the dried‐droplet method, analytes were co‐crystallized with matrix, whereas in the modified thin‐layer method analytes were deposited on the surface of matrix crystals. Model compounds, tetrabutylammonium iodide ([N(Bu) 4 ]I), cesium iodide (CsI), trihexylamine (THA) and polyethylene glycol 600 (PEG 600), were selected as the test analytes given their ability to generate exclusively pre‐formed ions, protonated ions and metal ion adducts respectively in MALDI. Results The strong matrix suppression effect (MSE) observed using the dried‐droplet method might disappear using the modified thin‐layer method, which suggests that the incorporation of analytes in matrix crystals contributes to the MSE. By depositing analytes on the matrix surface instead of incorporating in the matrix crystals, the competition for evaporation/ionization from charged matrix/analyte clusters could be weakened resulting in reduced MSE. Further supporting evidence for this inference was found by studying the analyte suppression effect using the same two sample deposition methods. Conclusions By comparing differences between the mass spectra obtained via the two sample preparation methods, we present evidence suggesting that the generation of gas‐phase ions from charged matrix/analyte clusters may induce significant suppression of matrix and analyte ions. The results suggest that the generation of gas‐phase ions from charged matrix/analyte clusters is an important ionization step in MALDI‐MS. Copyright © 2016 John Wiley & Sons, Ltd.