GIS: Gas Interface System
The GIS facilitates the direct measurement of CO2 (instead of graphite) in the MICADAS and thus of very small sample quantities (10-100μg C). By simplifying sample preparation and increasing automation, the GIS allows for a higher sample throughput than traditional graphite targets. In addition to discrete gas samples, which can be mixed into the helium stream by means of an ampoule cracker, the GIS can also process CO2 from the CHS or the EA. The CO2 supplied in the helium stream is selectively separated with a zeolite trap and later desorbed by heating to 450 ° C. The sample gas is then introduced at a constant flow into the gas ion source of the MICADAS through a gas-tight syringe as a mixture of 2-5% CO2 in helium.