Primary Trace Humidity Standards and SI-Traceable Trace Water Measurements in Ultra-High Purity Process Gases

Trace water is one of the most critical matrix contaminants in ultra-high purity (UHP) process gases, like argon (Ar) and nitrogen (N₂), and many others. Even trace amounts can severely degrade the quality of many products reliant on these gases. Despite its importance to advanced technology sectors, notably semiconductor manufacturing, it has proven quite difficult to realize preparative or analytical trace water metrology over the full amount fraction range needed or in the broad spectrum of industrially relevant matrix gases. Within the EU-funded PROMETH2O project consortium, this challenge has been addressed through the development or significant improvement of traceable measurement methods and standards spanning 5 nmol mol⁻¹ to 5 µmol mol⁻¹, tailored for use in UHP process gas production, such as Ar, N2 and hydrogen (H2). The measurement ranges were extended and the uncertainties were improved, while being consistent with current best practice at primary humidity standards laboratories. These capabilities were validated in applications relevant to process instrumentation and the gas industry. A distributed metrological infrastructure at various European National Metrology Institutes and partner sites now provides SI-traceable trace water measurements in various UHP, strongly supporting and extending the calibration capabilities for the gas and semiconductor industries and the associated stakeholders.