Patent ID: 8721988

Claim:
A method for direct gas measurement for measuring isotope ratio comprising: a) providing a device comprising: 1) a chamber wherein the chamber comprises: 2) a rigid enclosure; 3) a rigid lid for the enclosure wherein upon closure the lid and the enclosure form an airtight seal; 4) a port operably linked to a three-way stopcock wherein the stopcock is operably linked to the chamber in a first stopcock port and operably linked to a syringe in a second stopcock port, 5) at least one sensor port for airtight insertion of at least one gas sensor; and 6) at least one gas sensor for insertion into the at least one port; b) placing a subject contacted with an isotope in the chamber; c) closing the lid of the enclosure to provide an airtight chamber; d) measuring a gas concentration inside the airtight chamber; e) operably linking a self-sealing vacuum tube to the three-way stopcock at a third stopcock port; f) providing the three-way stopcock positioned to connect the syringe to the chamber but not outside air; g) withdrawing an air sample of defined quantity of air from the chamber; h) providing a three-way stopcock positioned to connect the syringe to the self-sealing vacuum tube but not the chamber; i) expelling the air from the syringe into the tube; j) removing the self-sealing vacuum tube from the adaptor; k) providing a three-way stopcock positioned to connect the syringe to outside air but not to the chamber; l) collecting a volume of outside air having the same volume as the air sample; m) providing a three-way stopcock positioned to connect the syringe to the chamber but not the outside air; n) expelling the outside air into the chamber, and o) detecting the isotope in a gas in the sample from step (g).