Gas Chromatography–Tandem Mass Spectrometry (GC-MS-MS)

Gas Chromatography–Tandem Mass Spectrometry (GC-MS-MS)

Gas Chromatography-Tandem Mass Spectrometry (GC-MS-MS) is a microanalytical technique that provides superior selectivity sensitivity and detail, when compared to GC with a single MS (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, 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.

Mass Spectrometry works by ionizing chemical compounds to generate charged ions, with a range of molecular masses, which are then separated based on their mass to charge (m/z) ratios and 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. Similarly, several types of mass analyzers such as magnetic sector, quadrupole, ion-trap, or time of flight (TOF) can be used, depending on continuous or pulsed mode detection, Mass spectrometer can work in both full scan and selective ion monitoring (SIM) modes.

Gas chromatography with Tandem Mass Spectrometry (GC-MS-MS) is a configuration that uses a GC followed by two Mass Spectrometers having the same type of mass analyzers. The GC-MS-MS overcomes the limitations of GC with a single MS (GC-MS), when working with complex sample matrices, more sensitive analysis requirements, isomeric compounds not separated by GC and gives additional mass and structural information. In a Tandem MS system (MS-MS), the ions (termed precursor ions) that are separated in the first mass analyzer enter a collision cell for further fragmentation The collision cell is filled with a suitable inert gas where collisions between the precursor ions and inert gas molecules are induced by an oscillatory field, causing bond breakage in the precursor ions to form product ions. The product ions undergo further separation in the second mass analyzer, yielding more information and reducing interferences and background noise. The GC-MS-MS is used to analyze a variety of volatile organic species.

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

• Drug detection
• Forensic investigations
• Environmental analysis
• Explosives trace detection
• Odour analysis of foodstuffs
• Pathological analysis

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

• Extremely sensitive and accurate technique
• GC-MS-MS allows selection of specific analytes for individual fragmentation. This allows more complex mixtures to be analysed more readily

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

• Research and development
• Quality control
• Toxicology studies
• Forensics
• Drug abuse prevention
• Environmental analysis
• Food industry
• Medical diagnostics