Comprehensive molecular imaging of photolabile surface samples with synchronized dual‐polarity time‐of‐flight mass spectrometry

Abstract

This work presents the unique features of a novel configuration of a synchronized dual-polarity time-of-flight mass spectrometer for comprehensive surface imaging. Mass spectrometry imaging of surface samples covering positive and negative ion modes is difficult due to rapid signal depletion. This limitation is overcome here by dual-polarity time-of-flight mass spectrometry (DP-TOFMS) via two separate TOF mass analyzers that are installed above a sample surface. The new instrument eliminates the polarity bias characteristic of most mass spectrometers, which is important for the analysis of samples with diverse physical and chemical properties. The experimental results show for the first time that the spatial distribution of positive and negative ions of various photolabile samples can be distinguished, including pigments and conventional matrix-assisted laser desorption/ionization samples. The different positive and negative ion distributions suggest that accurate quantitative information can only be obtained when the entire sample region is examined by DP-TOFMS, which was unfeasible in the past. Such a comprehensive diagnostic method is essential for the molecular imaging of trace compositions in delicate biological tissues, as demonstrated here with a Phyllanthus urinaria leaf that only produced ion signals in the first examination and not in the subsequent measurements.

Mass spectrometry imaging for plant biology: a review

“… Leaf MALDI, 200 µm Cuticular lipids Mounting of samples using double-sided tape, DHB matrix Vrkoslav et al ( 2010 ) GS-MS 2010 Eggplant ( Solanum melongena ) Fruit MALDI, 200 and 25 µm GABA, amino acids, carbohydrates Cryo-sectioning (14 µm), DHB matrix Goto-Inoue et al ( 2010 ) MS/MS 2010 Thale cress ( Arabidopsis thaliana ) Petal MALDI/LDI 10–40 µm Flavonol glycosides Perdian and Lee ( 2010 ) FT MS, LIT MS, MS/MS, and MS3 2011 Phyllanthus urinaria Leaf MALDI Photolabile metabolites Samples fixed on sample plates using thin layer of resin and kept in vacuum for 10 min before measurement. DHB matrix Hsiao et al ( 2011 ) – 2011 Eastern cottonwood ( Populus deltoides ) Stem MALDI, 50 µm Cellulose Sectioning on vibratome (50 µm), DHB matrix Lunsford et al ( 2011 ) MS/MS 2012 Petunia ( Petunia × hybrid) Leaf MALDI, 100 µm Cyclotides Cryo-sectioning (15 µm), CHCA matrix Poth et al ( 2012 ) LC–MS/MS 2012 Rabbiteye blueberry ( Vaccinium ashei ) Fruit ...…”

Lipid imaging by mass spectrometry – a review

“…70 The initial imaging data from plant leaves acquired on a dual polarity TOF system built from scratch, emphasized the advantages of simultaneous positive and negative ion image acquisition for samples that are photolabile or prone to molecular changes upon laser radiation. 71 Data conversion soware had to be developed to visualize mass selective images acquired on a QIT-TOF system. The rst images demonstrated successful spatial analysis of lipids in mouse brain.…”

Preparation of Homogeneous MALDI Samples for Quantitative Applications

“…In the current study, the imaging MS experiments are conducted using a laboratory-built synchronized dual-polarity TOF (DP-TOF) imaging mass spectrometer. 15 Commercial MALDI-TOF mass spectrometers with imaging capability are also suitable for such experiments. The mass spectrometer is operated in linear extraction and positive ion modes with optimized extraction delays.…”