1.1 ,This test method describes contaminant determination in fuel-cell-grade hydrogen as specified in relevant ASTM and ISO standards using cavity ring-down spectroscopy (CRDS). This standard test method is for the measurement of one or multiple contaminants including, but not limited to, water (H₂O), oxygen (O₂), methane (CH₄), carbon dioxide (CO₂), carbon monoxide (CO), ammonia (NH₃), and formaldehyde (H₂CO), henceforth referred to as “,analyte.”,