An investigation of the volumetric properties of L-alanine and sodium bromide in water at elevated temperatures and pressures

An optically coupled vibrating tube densimeter has been used to measure the relative densities of aqueous solutions of L-alanine and sodium bromide in the ranges 397 less than or equal to T/K less than or equal to 521 and 10 less than or equal to p/MPa less than or equal to 30. For the solute L-alan ine, the reported relative densities have been used to calculate apparent m olar volumes which, in turn, have been used in the calculation of partial m olar volumes at infinite dilution. The latter data are modeled using an equ ation of state of the type reported by Helgeson, Kirkham, and Flowers. This model is compared to those recently reported by Clarke and Tremaine. The r eported model for the temperature and pressure dependence of the apparent m olar volume of L-alanine in water is used to derive expressions for the app arent molar compressibilty and expansibility of this system. Calculated dat a for the latter property are compared to those available in the literature . In addition, the partial molar volume at infinite dilution for the alanin e side chain is calculated by combining the volumetric results reported in this manuscript for aqueous L-alanine solutions with those previously repor ted for aqueous solutions of glycine. Volumetric results for aqueous sodium bromide solutions have been compared to those calculated from a program by Archer that, utilizes the Pitzer Ion Interaction approach. (C) 2000 Academ ic Press.