GC-MS Principles and Diagnostic Applications

Flashcards covering the principles, separation mechanisms, and components of Gas Chromatography-Mass Spectrometry (GC-MS) as described in the lecture notes.

GC-MS

A technique combining gas chromatography and mass spectrometry to separate, identify, and quantify chemical compounds by resolving complex mixtures followed by molecular fingerprinting.

Carrier Gas

The inert (unreactive) mobile phase, commonly helium, nitrogen, carbon dioxide, or argon, used to carry the sample through the column at a constant flow rate typically between $10-50\,psi$.

Adsorption

A separation mechanism where solutes in a mixture selectively sorb onto sites on the surface of a stationary phase after displacing a solvent molecule.

Partition chromatography

A separation method where the stationary phase is a liquid supported on an inert solid, such as silica.

Bonded chromatography

A separation technique in which the liquid stationary phase is chemically bonded to a solid support.

Normal-phase chromatography

A method where the stationary phase is polar and the mobile phase is non-polar, resulting in non-polar compounds eluting earlier than polar ones.

Reverse-phase chromatography

The most common separation method where the stationary phase is non-polar (often hydrocarbon chains) and the mobile phase is polar.

Anion-exchange

A type of ion exchange chromatography where negatively charged ions are exchanged.

Cation-exchange

A type of ion exchange chromatography where positively charged ions are exchanged.

Size Exclusion

A separation mechanism based strictly on size where smaller particles travel a slower path through stationary phase pores, causing larger particles to elute first.

Affinity chromatography

A method relying on a specific ligand-target interaction to capture a single specific target on an inert stationary phase.

Electron Ionisation (EI)

An ionisation method using high-energy electrons to form fragment molecules, producing a unique fragmentation pattern used for identification.

Chemical Ionisation (CI)

An ionisation method where a reagent gas is used to form molecular ions, which affects both sensitivity and the degree of fragmentation.

Quadrupole

A mass analyser that filters ions using oscillating fields.

Ion trap

A component of a mass spectrometer that stores and ejects ions sequentially.

TOF (Time of Flight)

A high-resolution mass analyser that measures the flight time of ions to determine their mass.

Electron multiplier

A detector that amplifies the ion signal, which a computer then converts into a chromatogram and mass spectrum.

Transfer line

A component heated to $250-300\,^{\circ}C$ to prevent sample components from condensing as they move between the GC and MS.

Mass Spectrum

A graphical representation where the mass-to-charge ratios ($m/z$) of a molecule or its fragments are plotted according to their relative abundance.