Studies on the quantitative freeze-drying of aqueous solutions of some metabolically important aliphatic acids prior to gas-liquid chromatographic analysis

Abstract

These studies have shown that the over-all losses observed are due to volatilisation during the freeze-drying process. These losses are related to the variation of the vapour or sublimation pressures of the acids with temperature, and are also related to their latent heats of vaporisation or sublimation. Reliable data on the latent heats of vaporisation and sublimation of the acids of interest are seldom available and a method for the estimation of the latent heats, based on group contributions, has been developed. The reliability of the method, which is generally applicable to organic compounds, is discussed. Thermochemical data derived from the use of this method have been used in conjunction with reliable published experimental data to determine the optimum freeze-drying conditions for the complete quantitative recovery of all but the most volatile of the acids studied, with a minimum of preliminary experimental work.