A simple method for the determination of dissolved gases in natural waters. An application to thermal waters from Vulcano Island.

A new method for the determination of dissolved gas species in natural waters is presented. The method is suitable for field operations and ensures the preservation of the sample until analysis in the laboratory. This method is based on the equilibrium partition of gases between a liquid and a gaseous phase after the introduction of host gas. The host gas used depends on the gas species to be determined and on the technical features of the gas chromatograph. In this work pure Ar has been used. After shaking the sample for 5 min, a portion of gas was taken for gas chromatography analysis. From the concentration of gases in the gaseous phase and taking into account the partitioning coefficients of the various species, it is possible to derive the quantity of dissolved gases per litre of water and the partial pressures of the various gas species in equilibrium with water. This method has been applied to several samples of thermal water from Vulcano island. Helium and CO2 partial pressures of analysed samples were appreciably higher than those typical of waters in equilibrium with the atmosphere, thus indicating processes of interaction between the volcanic gases and groundwaters.