This document describes several test methods for measuring the ammonia amount fraction in natural gas and biomethane at the trace level (µmol mol-1). The suitable handling and sampling of pressurised mixtures of ammonia in methane that are applied to several different ammonia measurement systems are described. The measurement systems are comprised of readily available commercial spectroscopic analysers that are specific to ammonia. These NH3 analysers are considered as a black box in terms of their operation, which is dependent on the instructions of the manufacturer. The document describes suitable calibration and measurement strategies to quantify ammonia in (bio)methane around and above the 10 mg m-3 (14 µmol mol-1) level and applies to analysis within absolute pressure ranges of 1 bar – 2 bar, temperatures of 0 °C – 40 °C and relative humidity <90 %. References are also made to additional standards that are applied either to natural gas analysis or air quality measurements. In this document the matrix gas is always methane or biomethane and the measurand is the amount fraction NH3. NOTE            1 bar = 0,1 MPa =105 Pa; 1 MPa = 1 N/mm2.