This image shows the injectors (left) and detectors (right) on a dual-column GC. Each injector contains a rubber septum that can be pierced by a syringe needle. The internal volume is heated (to volatilise the sample) and continuously swept by the mobile phase (to carry the sample into the column).
The two detectors in this case are flame ionisation (lower) and electron capture (upper) detectors. An FID uses a hydrogen-air flame to combust any organic material eluting from the column; the current passing through the flame is measured to obtain the signal. The ECD uses a low-energy beta source to ionise the gas in the chamber.