Gas inlet system for isotope ratio analyzer and method of determining an isotope ratio

A gas inlet system for introducing gas into an isotope ratio analyzer,

• the gas inlet system including a reference system comprising:
• a first supply of a reference gas having a first known isotope ratio;
• a supply of a carrier gas,
• wherein the supplies of reference gas and carrier gas are each connected by respective reference and carrier gas lines to a first mixing junction where the reference gas and carrier gas combine;
• a mixing zone connected downstream of the first mixing junction wherein the combined reference gas and carrier gas mix together;
• an exit line for transporting the mixed gas from the mixing zone to the isotope ratio analyzer;
• a second mixing junction on the exit line from the mixing zone for mixing further carrier gas with the already mixed gas, the further carrier gas being supplied to the second mixing zone via a second carrier gas line;
• and
• an opening on the exit line, wherein the opening is downstream of the mixing zone.