An investigation into the factors responsible for the high volatility of liquid anaesthetic agents in high pressure fill gases
The partial pressure of a liquid in the vapour phase of a high-pressure gas is found to be experimentally higher than that calculated from Dalton's law of partial pressures. This deviation from ideality means that excessively high levels of liquids are found in the vapour phase of high-pressure gases. The research undertaken during this thesis has shown that it is possible to accurately predict vapour-liquid equilibria at high pressures, using a model which can be based on a minimal amount of vapour-liquid experimental data. This thesis also discusses possible explanations for excess levels of liquid being found in the vapour phase of a high-pressure gas. The model, used to calculate vapour-liquid equilibria in high-pressure systems, has been based on a large amount of experimental data, obtained through gas chromatographic analysis of the vapour phase of some high-pressure anaesthetic gas mixtures. The anaesthetic mixtures under consideration contain various liquid anaesthetic agents in selected fill gases. Gas chromatographic analysis of the high-pressure anaesthetic gas mixtures has also led to possible explanations of why excess levels of anaesthetic agents are found in the vapour phase of high pressure fill gases. For many years it was thought that molecular interactions between the liquid phase and the high-pressure gas were responsible or the excess levels of liquids found in the vapour phase of high-pressure fill gases. However, infrared spectroscopic analysis of the high-pressure anaesthetic gas mixtures have shown that there are no interactions taking place between the anaesthetic agents and the fill gases. To complement the research on liquid-gas anaesthetic mixtures, this thesis has also considered how the liquid anaesthetics interact with various liquid solvents. The interactions in the liquid phase have been analysed by measuring vapour pressures of the mixtures and also by nuclear magnetic resonance spectroscopy. NMR and vapour pressure measurements of mixtures of liquids have both been shown to provide interesting information about molecular interactions in the liquid phase.