Gas Chromatography-Mass Spectrometry (GC-MS)

Gas Chromatography-Mass Spectrometry (GC-MS)

Gas Chromatography-Mass Spectrometry (GC-MS) utilizes Gas chromatography (GC) to separate a chemical mixture into individual molecules followed by Mass spectrometry (MS) to identify the molecules. These two distinct micro-analytical techniques are coupled together in the GC-MS.

Gas Chromatography utilizes the principle that intermolecular (physical adsorption) forces between molecules in a gas and a solid surface depend upon the molecular structure and the nature of the solid surface. In a gas chromatograph, the sample chemical mixture is vaporized in an oven and transported by an inert carrier gas into a column (packed or capillary), containing the solid phase (termed stationary phase). The molecules carried in the gas (termed mobile phase), are eluted at different times from the column depending on the affinity of molecules for the stationary phase. The eluted molecules are detected when they exit the column with the signal intensity (peak) characterizing the nature and amount of each molecule. GC has limitations in distinguishing between molecules with identical affinity to the stationary phase, as they exit simultaneously.

Mass Spectrometry works by ionizing chemical compounds to generate charged ions, with a range of molecular masses. The ions are then accelerated in an electric field and separated in vacuum, depending on their mass as well as their charge. The separated ions are analyzed by spectrometry principles. Individual compounds have their own unique mass spectrum since every pure compound always produces the same family of ions. The Mass Spectrometry technique requires a very pure sample and does not work well for mixtures. Various methods for ionization such as electron ionization, chemical ionization and cold electron ionization are used, depending on the application. Mass Spectrometers can work in both full scan  and selective ion monitoring (SIM) modes.

By combining the functionalities of GC and MS, the GC-MS technique dramatically enhances analytical accuracy, overcoming the limitations of each.

Common Uses of Gas Chromatography – Mass Spectrometry (GC-MS)

• Drug detection
• Forensic investigations
• Environmental analysis
• Explosives trace detection

 Advantages of Gas Chromatography – Mass Spectrometry (GC-MS)

• Extremely sensitive and accurate technique

 Limitations of Gas Chromatography – Mass Spectrometry (GC-MS)

• The high temperatures (300°C) used in the GC-MS injection port (and oven) can cause thermal degradation of injected molecules affecting accuracy

 Industrial Applications of Gas Chromatography – Mass Spectrometry (GC-MS)

• Research and development
• Quality control
• Toxicology studies
• Forensics
• Drug abuse prevention
• Environmental analysis