A standard or sample is injected in the system and the absorbance of the gas is measured.  The absorbance of standards containing different amounts of the stable isotopes is used to prepare a calibration curve which can be used to determine the stable isotope concentrations.  The instrument makes use of Off-Axis integrated cavity output spectroscopy (ICOS) to simultaneously measure δ17O, δ18O and δ2H stable isotopes in water samples.

The O and H stable isotopes that can be used to study water cycles and to track water including rainwater, surface waters (rivers, ponds) and groundwater as it moves through the cycles.