(138b) Determination of Inorganic Salt Solubility by Headspace Gas Chromatography

This paper reports a novel method for determination of inorganic salt solubility in aqueous solution using headspace gas chromatography (HS-GC) techniques. Methanol and benzene alcohol were used as tracer compounds, in which their vapor-liquid equilibrium (VLE) behavior is affected by the salt concentration in the studied solution. Due to the molecular interactions in the solution, the VLE partitioning coefficient of the volatile species changes with different salt contents in the solution. Therefore, the concentration of volatile species in the vapor phase is proportional to the salt concentration in the liquid phase. As the salt concentration is increased by progressive removal of solvent, the concentration of the volatile compounds in the vapor phase will continue to increase until the salt concentration metastable limit is reached and a breakpoint will appear in the VLE curve. The solubility of the salts can then be determined by identification of the breakpoint and the corresponding amount of solvent removed. The solubility data of sodium carbonate and sodium sulfate in aqueous solutions obtained by HS-GC matches those determined by other methods in the literature. The present technique is applicable to a wide temperature range and can be easily applied to industrial solution systems.