The Thermo-Scientific Delta-Ray Laser Spectrophotometer analyzes the carbon (13C/12C) and oxygen (18O/16O) isotope ratios of carbon dioxide (CO2) in the atmosphere or in soil gases. The laser emits light with defined wavelengths. The different CO2 molecules (12C16O2, 13C16O2, 12C18O16O) absorb light with slightly different wavelengths, proportionally to their concentration; the analyzer calculates the ratios between the concentrations and derives the isotope ratios. A method has been developed for measuring directly in the field the isotopic ratios of the CO2 emitted by the soils of Vulcano and the relations with the gases dissolved in the waters of the hydrothermal stratum of the island.