Injection systems:

Several kinds of injection systems have been incorporated in commercial GC units. Almost as significant as column choice is the choice of injection method. The several approaches are mentioned below:

i) Direct injection: Injection within the packed column.

ii) Split injection and splitless injection: Those are adopted for capillary GC.

iii) Solid injection (moving needle): In that case, a solvent is evaporated before injection, resulting in improved separation of fast eluting elements.

iv) On-column injection: The sample is introduced within the column as a liquid, decreasing sample decomposition and providing reliable quantitative analytical results. This is considered as being an ideal solution for quantitative capillary GC.

v) Valve injection: Reproducibility of the valve injection volume is superior to any other injection technique. Valve injection could simply be automated that makes it extremely appropriate for routine on - line analysis.

vi) Thermal desorption cold trap injection: Gaseous samples are concentrated on an adsorbent tube. The elements are concentrated on a cold trap and then injected within the GC unit through rapid heating.

vii) Purge and trap injection: Aqueous samples are purged along with inert gas and the elements are concentrated on a cold trap. Entrained water is frozen out within the condenser. The elements are injected through rapid injection of the cold trap for multidimensional analysis; multiple switching intelligent controllers are available. A sample is pre-separated on a pre-column. Coeluting elements are trapped on a cold trap and reinjected within a column for further separation and analysis.