Proton Transfer in Time-of-Flight Secondary Ion Mass Spectrometry Studies of Frozen-Hydrated Dipalmitoylphosphatidylcholine

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• 作者：Thomas P. Roddy ; Donald M. Cannon ; Jr. ; Sara G. Ostrowski ; Andrew G. Ewing ; and Nicholas Winograd
• 刊名：Analytical Chemistry
• 出版年：2003
• 出版时间：August 15, 2003
• 年：2003
• 卷：75
• 期：16
• 页码：4087 - 4094
• 全文大小：148K
• 年卷期：v.75,no.16(August 15, 2003)
• ISSN：1520-6882

文摘

A frozen water matrix, as found in freeze-fractured frozen-hydrated cellular samples, enhances the ionization ofphosphatidylcholine lipids with static time-of-flight secondary ion mass spectrometry (TOF-SIMS). Isotopicprofiles of the phosphocholine ion from deuterated formsof dipalmitoylphosphatidylcholine (DPPC) have beenexamined under various sample preparation conditionsto show that ionization occurs through protonation fromthe matrix and is enhanced by the water present in freeze-fractured samples. The ionization of DPPC results inpositively charged fragment ions, primarily phosphocholine, with a m/z of 184. Other ions include the M + Hion (m/z 735) and an ion representing the abstraction ofthe two palmitoyl fatty acid groups (m/z 224). Freeze-fracture techniques have been used to prepare frozenaqueous samples such as liposomes and cells to exposetheir membranes for static TOF-SIMS imaging. Due to theimportance of surface water during SIMS analyses, sourcesof gas-phase water resulting from freeze-fracture wereexamined. Under proper fracturing conditions, watervapor, resulting from water in the sample and watercondensed onto the outside of the sample, is released intothe vacuum but does not condense back onto the surface.Combining the demonstrated enhancement of phosphatidylcholine lipid signal from water with the freeze-fracturepreparation techniques described herein demonstratespotential advantages of studying biological samples in afrozen-hydrated state.