Performance evaluation of a trace-moisture analyzer based on cavity ring-down spectroscopy: Direct comparison with the NMIJ trace-moisture standard

Abstract

The performance of a moisture analyzer (MA) based on cavity ring-down spectroscopy (CRDS) was evaluated by direct comparison with the primary trace-moisture standard developed at the National Metrology Institute of Japan (NMIJ). The limit of detection for trace moisture in nitrogen gas by the CRDS-based MA, expressed in amount fraction (mole fraction), was estimated to be 1 nmol mol −1 or less. The CRDS-based MA showed excellent performance in terms of linearity, accuracy, time response, stability, and reproducibility over four years. It was found for a moderate range of pressures and temperatures that we can measure trace moisture in nitrogen gas with a relative standard uncertainty of approximately 4% down to approximately 10 nmol mol −1, even using a simple CRDS-based MA that measures only the peak intensity of the absorption line, provided that the MA is properly calibrated on the basis of a reliable trace-moisture standard.