Rheology: how to characterize and to predict the evolution of W/O/W multiple emulsions.

Synopsis The purpose of this work was to compare the evolution of three multiple emulsions (ME) by different controls. The series of water-in-oil-in-water (W/O/W) multiple emulsions were elaborated and controlled by both the usual analyses which permitted the classification of the multiple emulsions with respect to their thermal stability, and the rheological oscillatory and flow analyses which are polyvalent methods. Further, these allow the 'identity card' of the multiple emulsion to be drawn, its evolution to be followed, and moreover, its behaviour being foreseen by simulating ageing by shear.

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Synopsis The main purpose of this article is to define multiple emulsions, their preparation (new materials and manufacturing processes) methods of characterisation and analysis, and their applications in cosmetology and pharmacy. The second part is devoted to a presentation of the investigation in our laboratory into the optimal manufacturing process to provide stable formulations. The study of release mechanisms from such formulations mainly shows a breakdown of multiple droplets which could be controlled by variation of solute concentration.

Nuclear magnetic resonance spectrometry and liquid chromatography of two bile acid epimers: ursodeoxycholic and chenodeoxycholic acid.

A specific reverse-phase high-performance liquid chromatographic (HPLC) technique is described for the analysis of bile acids and their conjugates in human serum. Precise quantitation is obtained using UV detection. 13C-NMR spectrometry suggests a structural explanation for the different HPLC retention times of chenodeoxycholic acid, its epimer (ursodeoxycholic acid), and their methyl esters.

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This study outlines the structure of the by-product obtained by the action of ascorbic acid on primary amines and alpha-amino-acids; the methods used are (13)C, NMR and infrared spectrophotometry. The chemical form is comparable to that of Ruhemann purple, obtained by the action of ninhydrin on alpha-amino-acids.