Patent ID: 7864323

Claim:
A method for measuring a concentration of a gas component in a measuring volume of a measuring gas, comprising: providing, in a reference cell, a gas component in a known concentration, the gas component in the reference cell being selected to contain a selected isotope in a known abundance ratio higher than a known natural-abundance isotope ratio of the same gas component; passing a light of a wavelength tunable light source along a single optical path through the measuring volume and the reference cell to a detector; when passing the light through the measuring volume and the reference cell, tuning the light source to sweep the wavelength of the light over an absorption line of the selected isotope and another absorption line of the remaining gas component; generating a signal by the detector, wherein the signal is indicative of the wavelength dependent absorption of the light; and calculating the concentration of the gas component in the measuring volume from a ratio of the detector signals at peaks of the absorption lines, based on Lambert's law, wherein the calculation is based upon the known abundance isotope ratios.