One such detector, known as a flame ionization detector (FID) analyzes the separated components from the GC by combusting them and analyzing the spectrum of said combustion. Each chemical compound exhibits a unique spectrum when combusted, In medicine, gas chromatography is used to test for toxins in the blood and hair, and is even sensitive enough to test a single hair for compounds deposited in it as it grows. It can easily detect quantities of compounds that are too small to test for with standard chemical tests. It can also be used on just about any type of tissue.