What component is used in a GC-MS but not in an LC-MS?

In a Gas Chromatography-Mass Spectrometry (GC-MS) setup, an electron source is employed to generate ions from the gaseous sample molecules. This process typically involves electron ionization, where electrons are emitted from the electron source and collide with the gas molecules, leading to the formation of charged particles. The resulting ions are then directed into the mass spectrometer for analysis.

In contrast, Liquid Chromatography-Mass Spectrometry (LC-MS) analyzes samples in the liquid phase and typically employs different ionization techniques. Common methods for ionization in LC-MS include atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), neither of which require an electron source in the same way as GC-MS does.

The utilization of an electron source is what distinctly sets GC-MS apart from LC-MS, as this component is critical for the generation of ions from vaporized samples during the GC phase. Thus, the electron source is a key component in GC-MS that is not found in LC-MS systems.