The ANITA2 (Analysing Interferometer for Ambient Air) instrument is a trace gas analyser designed to operate onboard the ISS to monitor the cabin atmosphere. ANITA2 can detect more than 30 of the most important trace gases in parallel. The advantages of an ANITA-type instrument include high sensitivity, accuracy, precision, and time resolution of the measurement data, as well as no consumption except electrical power and no production of waste. This also makes ANITA a steppingstone into the future, as a precursor system for crewed stations, bases, and exploration missions, including the Lunar Gateway and to/on the Moon and Mars. After a successful operation of ANITA1 for 11 months on-board the ISS in 2007 and 2008, the ANITA2 instrument was built in a contract between ESA, OHB and SINTEF and launched to the ISS in December 2021. ANITA2 operation started in March 2022 – after the deadline for this paper. This paper covers the pre-flight gas analysis. It gives a brief overview of the method of calibration, and of the final gas scenarios for the calibration and the associated gas estimation models. The calibration for 37 gases is described, and the test results from the final testing on 30 multi-gas mixtures are presented. The key results are the detection limits for the 35 trace gases in the calibration.