In dual inlet mode, pre-purified gas flows directly into the mass spectrometer, alternating with a known standard for isotope ratio determination. Each dual inlet measuring sequence can take up to 20 unknowns.

Solid or liquid samples are combusted in the elemental analyser, in a helium flow with the addition of oxygen. The gas species (N₂, CO₂) are separated by means of gas chromatography before entering the mass spectrometer.

In the MS source, the compounds are ionised and accelerated so that they can be separated according to their mass to charge ratio. The ion beam currents for each relevant mass/charge set is measured in Faraday cups for isotope ratio calculations. Using continuous flow, we measure δ¹³C and δ¹⁵N to a precision of 0.06 ‰.