What vapor does a Flame Ionization Detector (FID) primarily measure?

A Flame Ionization Detector (FID) primarily measures organic compounds, with a strong sensitivity to hydrocarbons such as methane. The way an FID works involves ionizing the vapors present in a sample when it is subjected to a flame; hydrocarbons produce ions or electrons when combusted, which can then be detected as a current.

Methane, being a simple hydrocarbon, is a primary focus in many applications that utilize FIDs, especially in the monitoring of emissions and leaks from sources such as underground storage tanks. The design of FIDs makes them particularly effective for detecting volatile organic compounds (VOCs), with methane being one of the most commonly encountered in environmental assessments.

Other gases mentioned, such as nitrogen and carbon dioxide, do not ionize in the same manner within the FID setup, making them less relevant for measurement by this device. Hydrogen, while it can be detected, does not have the same level of sensitivity or significance in the context of environmental monitoring and VOC analysis as methane does. Therefore, the choice of methane is accurate as the primary vapor measured by an FID.