Multiple inlet apparatus for isotope ratio spectrometry

A method of operating a multiple inlet apparatus for an isotope ratio spectrometer, the multiple inlet apparatus having a first bellows containing a first gas and a second bellows containing a second gas and the method comprising:

• adjusting compression of the first bellows to a first compression value such that a first pressure of the first gas is equal to a target pressure value;
• adjusting compression of the second bellows to a second compression value such that a second pressure of the second gas is equal to the target pressure value;
• determining a first compression function configured to maintain the first pressure at the target pressure value and a second compression function configured to maintain the second pressure at the target pressure value;
• continuously compressing the first bellows according to the first compression function until a first measurement of first isotope ratios for the first gas is complete;
• and
• continuously compressing the second bellows according to the second compression function until a second measurement of second isotope ratios for the second gas is complete.