Gas chromatography detection. Several configurations have been used with GCs. Both sampling and injection into the column have been improved over the years. (A) Manual GC injection was done with syringes. (B) Auto-injector-facilitated injections brought higher accuracy and could process a large number of samples. (C) Adsorption/desorption units were used to accumulate ethylene for minutes to increase the detection limit to the nL L−1 range. Several detection schemes were implemented using a non-destructive, although not sensitive sensor, such as the thermal conductivity detector (TCD). Later on detectors sensitive to hydrocarbons – the flame ionization detector (FID) – or to aromatic and olefin hydrocarbons – the photoionization detector (PID) – were developed and became the most commonly adopted detector technologies.