Gas Chromatography Mass Spectrometry (GC-MS)

Gas chromatography (GC) can separate volatile and semi-volatile compounds well, but it cannot identify them. Mass spectrometry (MS) can provide detailed structural information for most compounds, allowing them to be identified accurately, but it cannot separate them easily. Therefore, in the mid-1950 s, some scholars suggested combining the two technologies.

GC-MS is a very favorable synergistic combination, because compounds that are easy to be analyzed by GC (low molecular weight, medium or low polarity, in ppb-ppm concentration) also meet the requirements of MS. In addition, both analyses are performed in the same aggregated state (vapor phase). The only conflict between GC and MS is the different working pressures, i.e., atmospheric at the GC column exit and low (10^-5 - 10^-6 Torr) in the ionization chamber, respectively. This drawback was overcome by the technical introduction of high efficiency vacuum pumps (turbo-molecular and gas jet pumps) and especially by the introduction of GC capillary columns inserted directly into the ionization chamber of the mass detector ^[1]. Due to its high sensitivity, peak resolution and reproducibility, GC-MS has become the most important tool for the identification and quantification of volatile and semi-volatile organic compounds in complex mixtures.

Principle of GC-MS

• In GC, the sample solution is injected into the GC inlet where it is vaporized and directed onto the chromatographic column by the carrier gas (such as helium or nitrogen). The sample molecules are separated through different interactions between the carrier gas phase and the stationary phase ^[2].
• Once the components leaving the GC column enter the mass spectrometer, they are bombarded with high-energy electrons, ionized and fragmented into smaller, positively charged ions. The ionized molecules and fragments are then accelerated through the instrument's mass analyzer. It is here that ions are separated based on their different mass-to-charge (m/z) ratios. The separated ions are detected by a detector, which generates a signal proportional to the number of detected ions.

Applications of GC-MS

GC-MS is highly sensitive, precise, and selective, making it an essential tool in many fields where accurate chemical analysis is required. Its main applications are as follows.

• Environmental Monitoring: Analysis of air, water, and soil samples to detect and quantify pollutants, such as volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and pesticides.
• Food and Flavor Analysis: Identification and quantification of aroma compounds in food, beverages, and fragrances.
• Forensic Science: Detection and analysis of drugs, explosives, and other illicit substances in criminal investigations.
• Clinical Diagnostics: Measurement of drugs, hormones, and metabolites in patient samples for disease diagnosis and monitoring.
• Pharmaceutical Analysis: Characterization and quantification of drug compounds and their impurities in drug development and quality control.
• Petrochemical Analysis: Identification and quantification of hydrocarbons in petroleum products and crude oil.
• Academic Research: Provides the possibility of analyzing new compounds to achieve the characterization and identification of synthetic or derivative compounds. It yields useful information that can be used in international research publications.

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References

1. Stashenko, E.; Martínez, J. R. Gas chromatography-mass spectrometry. Advances in gas chromatography. 2014: 1-38.
2. Wittmann, C. Fluxome analysis using GC-MS. Microbial cell factories. 2007, 6(1): 1-17.

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