Metrological Validation of NH3 Reference Gas Calibration for the MetNH3Energy Project Based on ISO 6143

Ammonia (NH3) is emerging as a key energy carrier in the context of the European Union’s drive towards decarbonisation, serving as a hydrogen carrier and direct fuel in maritime and power generation sectors. Accurate and traceable measurement of NH3 purity is essential across the entire ammonia value chain. This article describes the work carried out by the Reference Gas Laboratory (LGR) of the Instituto Português da Qualidade (IPQ) within the framework of the European Partnership on Metrology project MetNH3Energy. This work presents the calibration of NH3 reference gas mixtures according to ISO 6143 using a first-order linear fit with three certified reference gas standards in nitrogen matrix at nominal mole fractions from 25 µmol/mol to 1001 µmol/mol. While the ISO 6143 comparative approach is well established, its systematic application to NH3 across this concentration range, together with an assessment of the nitrogen-to-air matrix effect relevant to IPQ’s air-matrix reference mixtures, has not previously been reported and extends the NH3 measurement capabilities currently available through the BIPM Key Comparison Database. The validation of the NH3 calibration method was carried out on three consecutive days using the normalised error (En) statistical tool and repeatability and intermediate precision studies. All En values obtained were within the acceptance criterion |En| ≤ 1, confirming the validity of the calibration method. Repeatability and intermediate precision components were found to be well below the calibration uncertainty, demonstrating the robustness of the measurement procedure. These results support the establishment of new Calibration and Measurement Capabilities (CMCs) for NH3 at IPQ, contributing to the metrological infrastructure for ammonia in emerging energy applications. This work therefore represents the first rigorous validation of the NH3 calibration method at IPQ, providing the metrological foundation needed to support the emerging ammonia energy sector.