Gas Inlet System for Isotope Ratio Analyzer and Method of Determining an Isotope Ratio

Abstract

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; and an opening on the exit line, wherein the opening is downstream of the mixing zone. Also provided is a method of determining an isotope ratio.

What is claimed is: 
     
         1 ) A method of determining an isotope ratio by optical spectrometry, comprising:
 supplying a flow of reference gas at a known isotope ratio;   supplying a flow of carrier gas;   mixing the reference gas with the carrier gas thereby diluting the reference gas with the carrier gas and flowing the diluted reference gas to an optical isotope ratio analyzer to measure the isotope ratio of the reference gas;   supplying a flow of sample gas of unknown isotope ratio;   mixing the sample gas with the carrier gas thereby diluting the sample gas with the carrier gas and flowing the diluted sample gas to the optical isotope ratio analyzer to measure the isotope ratio of the sample gas;   wherein the flow of carrier gas is varied to match a concentration of reference gas in the carrier gas to a concentration of sample gas in the carrier gas or vice versa; and correcting the measurement of the isotope ratio of the sample gas by the measurement of the isotope ratio of the reference gas.   
     
     
         2 ) A method according to  claim 1 , wherein the optical isotope ratio analyzer is a laser spectrometer. 
     
     
         3 ) A method according to  claim 1 , wherein the reference gas is a substantially pure gas and the carrier gas is substantially free of the reference and sample gas. 
     
     
         4 ) A method according to  claim 1 , wherein the flow of carrier gas is controlled to match the concentrations of reference gas and sample gas in the carrier gas to an optimum concentration of the isotope ratio analyzer. 
     
     
         5 ) A method according to  claim 4 , wherein the optimum concentration of the isotope ratio analyzer is a concentration in the range 200-4000 ppm. 
     
     
         6 ) A method according to  claim 5 , wherein the flow of carrier gas is dynamically controlled. 
     
     
         7 ) A method according to  claim 1 , wherein the reference gas and the sample gas is selected from the group consisting of: CO2, CH4, C2H6, CxH(2x+2), water vapor, CO, small hydrocarbons, alcohols, aldehydes, NOx, NxOy, H 2 S, nitrogen, oxygen, and hydrogen. 
     
     
         8 ) A method according to  claim 7 , wherein the carrier gas is selected from the group consisting of: air, nitrogen, helium and argon. 
     
     
         9 ) A method according to  claim 5 , wherein the reference gas and sample gas is CO2 and the carrier gas is CO2-free air or CO2-free nitrogen. 
     
     
         10 ) A method according to  claim 5 , wherein the pressure of gas entering the optical isotope ratio analyzer is around atmospheric pressure and further comprising pumping the optical isotope ratio analyzer using a vacuum pump so that the pressure in the optical isotope ratio analyzer is below atmospheric pressure.