GC Interface

What is the GC–MS interface?

GC–MS couples gas chromatography to mass spectrometry.

Unlike LC–MS, GC is particularly compatible with MS because compounds leave the GC column already in the gas phase.

Sample pathway

Sample → GC injector → vaporisation → GC column → heated transfer line → ion source → mass analyser

The carrier gas transports analytes through the GC column.

Compounds separate according to their interactions with the stationary phase and their volatility.

Entering the MS

The end of the GC capillary column usually extends through a heated transfer line toward the MS ion source.

The carrier gas and analytes enter the mass spectrometer continuously.

The vacuum system removes the carrier gas while ions generated from the analytes are analysed.

Common ionisation techniques

GC–MS commonly uses:

Electron ionisation (EI) — energetic electrons ionise molecules and often produce extensive fragmentation.

Chemical ionisation (CI) — reagent gas chemistry produces generally softer ionisation and can provide stronger molecular-mass information.

Why temperature matters

The interface must remain hot enough to prevent analytes from condensing.

If the transfer line is too cold:

analyte condensation → peak broadening/loss → reduced sensitivity

Excessive temperatures can also be undesirable for thermally unstable compounds.

Common problems

Typical GC interface problems include:

Key takeaway

The GC interface maintains a heated, low-dead-volume pathway between the GC column and the MS ion source.