Basics of GC

The injector’s role

To introduce into the chromatograph a precise volume of sample for analysis without disturbing the flow of the gaseous mobile phase in the system.
For non-volatile samples at room temperature, to vaporize them so that they are transported towards the separation column by the carrier gas.

$Diagram of the injector. In the septum, which ensures the sealing during the injection. On the left, with an arrow entering the injector the carrier gas. Vertically, along the injector, the liner. In the central axis of the injector: the separation column. At the top of the injector, on its right, a septum purge pipe, which avoids contamination between injections. Finally, at the outlet of the injector, the leak or division, which allows to fractionate the quantity of injected sample.$

The injector’s role

To vaporize the sample.
To introduce the volatile compounds into the separation column.

Diagram showing the 3 steps of the injection, in 1 the vaporization of the sample, in 2 the introduction of the volatile compounds in the separation column, in 3 the division at the outlet of the injector.

The injector’s role

To prevent the distortion of chromatographic peaks by rapid injection and non-saturation of the stationary phase: division mode (split).

Diagram showing the volumes and flow rate in the injector. Inlet flow rate 100mL/min, column flow rate 2 mL/min (2% injected), leakage flow rate 98ml/min, and finally the liner volume 1mL, with an injection time of 0.6s.

The injector’s role

Very diluted sample in a solvent, no risk of column overloading: without division (splitless mode)
Splitless mode in two stages:
- Transfer of the sample to the column head with condensation of solvent
- Solvent vaporization and initiation of analyte elution

Diagram showing the 2 steps in splitless mode. 1 the leak is closed, inlet flow 2mL/min. 2 the leak is open, with a leak flow of 48mL/min and an inlet flow of 50mL/min.

Split/splitless injection?

Adapting the injection type to the sample, especially taking into account its concentration.
2 curves showing the differences between splitless without flow divider and splitless with flow divider. The splitless curve shows more variations.

2 curves showing the differences between splitless without flow divider and splitless with flow divider. The splitless curve shows more variations.

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