Gas Chromatography

The concept of GC-MS is used in molecular biology and has diverse applications. GC-MS denotes the  Gas chromatography- Mass Spectrometry method, a combination of two analytical methods in chemistry. We will be discussing the two of them, their principle, and everything remotely connected to the workings of the GC-MS

What is Gas Chromatography?

Gas chromatography is a type of chromatography that is a separation technique. 

Putting things in perspective, separation techniques are methods and procedures that are used in the identification and proper separation of two or more substances in a mixture. It is used mostly to detect known or unknown substances in certain mixtures, and also to extract useful substances from other kinds of mixtures.

Examples of separation techniques are

• Magnetization
• Decantation
• Evaporation
• Filtration
• Distillation
• Fractional distillation
• Crystallization
• Chromatography

Chromatography is a separation technique that involves the movement of the said mixture that us to be separated in phases; that is it is a method involving the distribution of the mixture’s components in phases(usually a stationary and mobile phase)

We have different types of chromatography but some of the popular ones are

• Paper chromatography
• Column chromatography
• Thin-layer chromatography
• Partition chromatography 
• Gas chromatography

Therefore, gas chromatography is a separation technique used in analytical chemistry that involves the separation of a substance that is volatile. It is used for samples that contain substances with different boiling points. The mobile phase is an inert gas while the stationary phase is porous.

What is Mass Spectrometry?

Mass spectrometry is also another technique used in analytical chemistry, but its working is on the mass to charge ratio.

Hence, mass spectrometry can distinguish between different chemical substances since each one has different atoms that carry different mass-to-charge ratios

Its principle is based on the separation of matter via subsection to electric and magnetic fields. Charged particles will either be attracted or repelled(based on the charge they are carrying)by the electric field; while the magnetic field will deflect them based on their heaviness; that is to say their mass.

The results will then be shown on a mass spectrum, a graph that depicts the mass to charge ratio as a function of ion signals gotten from the spectrometer.

What is GC-MS?

GC-MS is an analytical method that integrates the elements of both gas chromatography and mass spectrometry used in the identification of different samples and substances in a given mixture. 

It is said to be the gold standard in the detection of substances as it can detect micro amounts of a certain substance in a given sample. It also gives results based on a 100℅ specific test, which implies that it can identify even trace amounts of any substance inside a sample.

Note The high temperatures used in the GC MS injection portion cause non-conscious vaporization of the sample, thus making the machine detect products gotten from the vaporization instead of the actual injected sample

Instrumentation used in GC-MS

The instrument /equipment used in GC-MC is the gas chromatograph and the mass spectrometer. They work hand in hand to detect and isolate substances from the mixture.

The types of gas chromatograph used include 

• Purge and trap Gas chromatograph
• Purge closed loop has chromatograph

Types of Mass spectrometers used in GC-MS are

• Quadrupole Mass Spectrometer
• Ion trap mass spectrometer
• Magnetic sector mass spectrometer
• Tandem quadrupoles
• Time of flight mass spectrometers

Principle behind GC-MS

The principle in the GC-MS technique is simple: the separation of the chemical substance by the gas chromatograph, and the detection of the components by the mass spectrometer.

The sample is injected into the gas chromatograph and vaporized, then its components are inserted into an inert gas e.g. nitrogen. The gas will then help separate the different components as they pass through the porous stationary phase.

When they come out, they are subjected to the spectrometer for ionization. The components are bombarded with high-velocity moving electrons and the components will become fragmented, hence allowing them to be detected as they will send their signals to the spectrometer.

There are different methods of ionizing the sample and they are given below 

• Electron Ionization
• Cold electron ionization
• Chemical ionization.

For electron ionization, it is the process described above. The components are bombarded with free electrons to excite the molecules and cause them to fragment.

In cold electron ionization, the components are first fooled to an appreciable degree to reduce the rate of fragmentation and to obtain molecules with better information.

Thirdly, chemical ionization involves the introduction of a chemical e.g. methane into the mass spectrometer. This causes a chemical reaction to take place and ionization of the components will take place. We have two types of this; positive chemical ionization and negative chemical ionization.

Applications of GC-MS

GC-MS has diverse applications in different fields of study. 

• Environmental monitoring and cleanup

GC-MS is used to track and observe the movement of organic pollutants in the environment.

• Chemical Forensics

As an analytical tool, the GC-MS can analyze the particles gotten from a human body which can serve to link a suspect or criminal to a crime.  It is also a very accurate procedure.

• Law enforcement

It is used in the identification and detection of illegal narcotics. It can also be used in forensic toxicology to find traces of drugs or poisonous substances in human or animal specimens.

• Security

GC-MS-linked explosive detectors are being used in places to heighten security in and around those areas.

• Sports anti-doping analysis

GC-MS is used to test urine samples of athletes to detect doping agents and performance drugs.

Conclusion

The GC-MS is a great analytical tool that can be used in a plethora of ways. Its high level of specificity and precision in identifying substances makes it stand out compared to other forensic methods of identification.