The present invention relates to a system of analysis, which can be used in a mobile laboratory in a drilling site situation or in a similar situation, suitable for measuring (preferably in relation to at least two partially gaseous species, which derive preferably from a mixture extracted from a drilling mud, for example, methane, ethane, propane and/or any other heavier hydrocarbons) the quantities of the different isotopes of at least a same chemical element (preferably the quantities of 13C, carbon isotope with 6 protons and 7 neutrons, and of 12C, carbon isotope with 6 protons and 6 neutrons, respectively) by means of a laser isotopes analyzer regulated for a single, at least partially gaseous species which contains said chemical element.
