A flame ionization detector operates on the principle that combustible chemicals produce ions during combustion which can be detected as a current. In practice, a target gas stream is directed into a flame (typically a hydrogen-air flame) which results in the combustion of target chemicals and the production of positively charged ions and electrons. The resulting current is sensed by electrodes placed close to the flame. FID is a non-specific detector, i.e., any molecule with carbon and hydrogen atoms will produce a response.