This method is for determining low concentrations (0.5 to 500mol-ppm) of carbon monoxide (CO) and carbon dioxide(CO₂) in high purity hydrogen and other gas-phasesamples. The lower limit of detection for either CO orCO₂ in hydrogen is 0.5 mol-ppm. The lower limit ofdetection for CO in samples containing high concentrations ofoxygen, argon or nitrogen is 5 mol-ppm. Methane at concentrationsabove 5 mol-% will interfere with the determination of carbondioxide.