FID sensitivity:
Further to normal carrier gas, auxiliary gases of hydrogen and air are required to fuel the flame. The hydrogen flame, being perhaps the most popular detector within gas chromatography, is very sensitive and under proper conditions, the detector is capable for responding to a few parts per billion of the solute component. In common, good sensitivity and stability are acquired along with a carrier gas flow of 30 cm3/min, hydrogen flow of 30cm3/min and air flow at 300 cm3/min.
Figure: FID sensitivity vs H2 flow
The FID has the widest linear range of any detectors in general use (106 to 107). The mixture of high sensitivity and huge linear range makes the FID the choice in trace analysis.