The injection system is the place where the sample is introduced onto the GC column. Depending on the amount and type of sample as well as the dimension and the type of column, there are several injectors available:

• Direct injector: This injector is used for packed columns and wide-bore capillary columns. It is used for liquid samples. These samples can be pure liquid components or solutions of liquid and/or solid samples. Direct injection is practically always carried out at high temperatures and therefore a temperature control unit is required.
• Split injector: This is the most universal and most widely used injector for capillary columns. The split injector is derived from the direct injector and is also based on rapid evaporation.
• Splitless injector: This type of injector is used for highly diluted samples (trace injection).
• Cold on-column injector: This injector is used for direct injection of liquid samples onto capillary columns.
• Programmed-Temperature vapourizer injector: This injector allows large volumes of sample to be introduced into the injector, with or without simultaneous evaporation of excess solvent. After solvent evaporation, the split vent is closed, then the injector is heated up to transfer target compounds to the column.

Direct versus split injection