The properties of liposomes are known to be influenced by many factors. Especially, the stability of liposomes is effected by the change of the phase transition temperature (T,) of lipids. In this work, the keto-enol tautomerism of benzoylacetoanilide (BAA) was used to measure the T,. When BAA is added to the liposome suspensions, the ketonic form exists in bulk water and the enolic form in bilayers of the liposomes. Moreover, when the temperature for the system is changed, the change of the ratio of the enolic to ketonic absorances can be expected to show a sharp peak at a temperature corresponding to the T, of lipids. Therefore, the T, value for liposomes can be estimated from the change of the absorbance ratio caused by the change of the temperature for the system. Three kinds of phosphatidylcholines were used as the standard lipids, and these data were used for determination of the T, of hydrogenated egg lecithins.Further, additional effects of cholesterol in liposomes were investigated in the same way. These results indicated that the T, values of hydrogenated egg lecithins decreased linearly with the increase of iodine values, and the T, values for most liposomes dropped suddenly above the concentration of about 15 mol ?6 cholesterol. This suggests that above this concentration cholesterol molecules are incorporated homogeneously into the bilayers and then the T, values decrease due to formation of the mixed layers such as a palisade type between cholesterol and lipid molecules. Consequently, this method for T, determination can be applied even in the diluted aqueous solution with concentration below 0.15% of lipids and is very simple and useful in comparison with common methods.

The creaming behavior of an oil-in-water (O/W) emulsion was quantitatively evaluated via resonance-enhanced multiphoton ionization time-of-flight mass spectrometry. Styrene O/W emulsions were prepared with initial styrene concentrations of 1 and 4 g/L, and the height at the center of the sample was monitored. A peak area of the molecular ion of styrene was set as the signal intensity, for which a time profile was constructed from a series of mass spectra. As a result, the averaged time profiles showed that the signal intensities increased once and then decreased with the onset of creaming. In addition, in order to fit an experimentally obtained time profile, a modified fit function was proposed. Based on the fit results, the ratios of the increases and decreases in signal intensities were different between the two emulsions-higher in the case of an O/W emulsion with a higher initial oil concentration. On the other hand, the duration of the enhancement of the signal intensity with the onset of creaming was independent of the initial oil concentration. The present method offers the possibility to quantitatively evaluate the creaming behavior of an emulsion without pretreatment, and, therefore, would be useful for confirming the stability and quality assurance of emulsions.