Analysis of the oil-water interface by XPS at low temperature

protocol was set up to achieve good control and monitoring of the XPS analysis of hydrated specimens, which involves the ability to freeze the sample before its introduction into the spectrometer, to maintain ice under UHV and to control ice sublimation. The methodology was applied successfully to a model system consisting of a drop of water deposited on a film of triolein containing traces of a phospholipid (dipalmitoyl phosphatidylcholine). Phosphorus and nitrogen, characteristic of the phospholipid, were demonstrated to be accumulated at the spot of the initial oil-water interface. The redistribution of the phospholipid after oil melting could be monitored in real time. The method is promising not only to study surface rearrangements on hydrated systems after water removal but also to get analytical information on gas-water interfaces and on interfaces between two liquids differing according to volatility. Copyright (c) 2008 John Wiley & Sons, Ltd.