Isotope ratio measurement

An isotope ratio spectrometer system comprising:

• an isotope ratio spectrometer;
• one or more processors;
• and
• one or more non-transitory computer-readable media having computer program instructions stored therein, the computer program instructions being configured such that, when executed by one or more processors, the one or more processors cause the performance of the steps of:
• measuring first isotope ratios and first signal intensities for a first reference in the spectrometer, over a first measurement time period, a first relationship comprising a relationship between the first isotope ratios and the first signal intensities being determined;
• establishing a time A within the first time period, at which a signal intensity for the first reference is considered the same as a signal intensity for the sample at time X and thereby identify a first reference isotope ratio for the time A, using the first relationship;
• measuring sample isotope ratios and sample signal intensities in the spectrometer, over a second measurement time period subsequent to the first measurement time period;
• measuring second isotope ratios and second signal intensities for a second reference in the spectrometer, over a third measurement time period subsequent to the second measurement time period, a second relationship comprising a relationship between the second isotope ratios and the second signal intensities being determined;
• establishing a time B within the third time period, at which a signal intensity for the second reference is the considered same as a signal intensity for the sample at time X and thereby identify a second reference isotope ratio for the time B, using the second relationship;
• and
• estimating a reference isotope ratio for a time X within the second measurement time period, based on the first relationship and the second relationship, wherein estimating the reference isotope ratio for the time X within the second measurement time period is based on the first reference isotope ratio for the time A, the time A, the second reference isotope ratio for the time B and the time B.