中央研究院 原子與分子科學研究所

Abstract
RATIONALE: In most of the previous studies, the ratios of desorbed ions and neutrals from matrix-assisted laser desorption ionization (MALDI) were measured outside the common MALDI conditions. In this work, we measured the ratios in common MALDI conditions.
METHODS: Ions were detected using a time-of-flight mass spectrometer in combination with a time-gated ion imaging detector. Mass-resolved desorbed neutral molecules at different angles and velocities were measured using a modified crossed molecular beam apparatus.
RESULTS: The upper limit of ion-to-neutral ratio from pure2,5-dihydroxybenzoic acid is 4´10^-9at laser fluence 40 J/m², it increases to 3´10^-7at laser fluence 250 J/m². The ratios ofmatrix from the mixture of 25DHB and analyte remain in the same order of magnitude as pure 25DHB. However, the ratio ofanalyte depends strongly on the analyte.Values as large as 10^-3-10^-4for bradykinin and as small as <10^-8for glycine were observed at laser fluence ~100 J/m².
CONCLUSION: The ion-to-neutralratios of 25DHB matrix measured in this work are much smaller than some of the values reported in previous work using different methods and/or under different MALDI conditions.