The scientists used gas chromatography to measure low levels of carbon monoxide in the air. They separated carbon monoxide from other air components, turned it into methane using a nickel catalyst, and then detected it with a flame-ionization detector. They found a direct relationship between the peak size and carbon monoxide concentration in the range of 0.5 to 1000 parts per million. The method could detect carbon monoxide levels as low as 0.2 parts per million.