How does a Flame Ionization Detector (FID) work and what are its applications?

FID burns sample in hydrogen/air flame; organic compounds produce ions proportional to carbon content. Ions create current between electrodes measured by electrometer. Advantages: universal hydrocarbon response, wide linear range (10^6), stable and reliable. Applications: total hydrocarbon measurement (THC), EPA Method 25A emissions, GC detector for organic compounds. Considerations: does not respond to inorganics (CO, CO2, H2O), requires H2 supply, and response varies with carbon oxidation state. FID provides excellent sensitivity (ppm to ppb) and remains standard for VOC measurement despite newer technologies.