Learn the principle, types, applications of gas chromatography and how gas chromatography is works.
What is Gas Chromatography?
In analytical chemistry, gas chromatography (GC) is used to separate and determines the content of various analytes that can be vaporized without decomposition. The separation in gas chromatography is dependent on compound volatility. The more volatile compound is rapidly isolated, while the less volatile compound is slowly released. In this type of chromatography, the carrier gas is used as a mobile phase, usually, an inert gas such as nitrogen and helium is used, and as a stationary phase, a very thin layer of polymer or liquid on an inert solid support, inside a metal or glass tube is used, called as a column.
Gas Chromatography Principle:
Gas chromatography follows the principle of the partitioning of volatile compounds with the mobile phase (gaseous) and stationary phase (liquid or solid). The separation speed of molecules through the column is based on the affinity for the stationary phase; the molecules which are partitioned in the gas first come out, whereas the other eluted later.
The sample solution of complex mixtures injected into the instrument enters a stream of gas that travels through the column and in which the different components are separated. The detector (usually FID, GC-MS) determines the number of analytes exiting the column. For analysis of a sample with an unknown concentration, a standard sample with a known concentration is injected into the sample injector. To calculate the concentration, the peak area and retention time of the standard sample compare with the test sample. In this type of chromatography, gas is always used as a mobile phase and the stationary phase is either solid or liquid.
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Gas Chromatography Diagram:
Experimental Procedure of Gas Chromatography:
Before beginning a Gas Chromatography experiment, we must recognize the various components essential to perform the process.
It is composed of four major components.
1. Carrier gas: Since, carrier gas (hydrogen, helium) is used as a mobile phase in GC it plays an important role in isolation.
2. Injector: The port is intended to inject samples into the GC by manual or autosampler.
3. Oven: The temperature of the column in GC is controlled by an oven to manage the separation and retention time of the analytes.
4. GC column: A column, in which the molecules, depending on their affinity with the mobile phase (gas) and the stationary phase are separated into individual analytes.
5. Detector: The detector used to determine the composition and concentration of a sample.
Procedure of Gas Chromatography:
- Maintain inlet and outlet pressure of gases with the help of a regulator mounted on the control panel.
- Install the required column (Packed/Capillary) and it should not leak.
- Create and download the method and sequence from software and before injection ignites the flame. The parameters such as injector temperature, detector temperature, oven temperature, flow/pressure of the gas, and sequence of the sample/vial, Etc.
- Prepare samples as needed.
- Download the method of the software and ignite the flame before injection.
- Saturate GC column with mobile phase until baseline.
- Inject the sample manually by syringe or Autosampler by filling the vial at least halfway.
- Depending on their affinity to the stationary phase, the components in the sample mixture are isolated from the
- At different times the separated analytes reach the detector and are recorded by the computerized system.
- From the chromatogram, the retention time (RT), peak area, column efficiency, tailing factor, peak height, and the number of theoretical plates can be calculated.
Gas Chromatography Applications:
- Gas chromatography is commonly used as a routine analytical technique in pharmaceutical industries.
- It is used for both medicinal and forensic applications for the quantification of drugs and their metabolites in blood and urine.
- GC is used in pesticide and volatile analysis.
- Gas chromatography techniques are used in many fields of forensic science.
- GC is used in the analysis of flavor, fragrance, and food products.
- GC is used to analyze the organic compounds in environmental samples.
Advantages of gas chromatography:
- GC gives high sensitivity when used with a thermal detector.
- GC has an additional column length compared to high-performance liquid chromatography, so it is possible to separate complex mixtures of analytes with high resolution.
- The analysis of the samples is faster than HPLC.
- Gas chromatography has a high-resolution power than other methods such as HPLC, TLC, and column chromatography, etc.
- A small amount of sample is required for separation.
- This method provides comparatively high accuracy and precision.
Disadvantages of gas chromatography:
- A major disadvantage of GC is that only volatile samples can be analyzed.
- Except for mass spectroscopy, most GC detectors are destructive.
- It is unable to recover isolated samples.
- In HPLC and TLC selectivity is best compared to GC, since a mobile process can be easily replaced changed.
Commonly asked questions on chromatography are as follows.
What is the basic principle of GC?
GC separation is based on different distributions of the component molecules which are separated between the stationary phase (column) and the mobile phase (gas).
What are the types of gas chromatography?
Based on the stationary phase used, there are two types of gas chromatography, such as gas-liquid chromatography (GLC) and gas-solid chromatography (GSC).
What is the major difference between GC and HPLC?
The main difference between GC and HPLC is the mobile phase used. In GC the sample mixture compounds are separated using gas as a mobile phase and in HPLC the liquid is used as a mobile phase.
What is the major advantage of gas chromatography?
The major advantage of GC is a rapid analysis with high efficiency.
How many types of GC detectors are there?
Flame ionization (FID), Electron capture (ECD), Thermal conductivity (TCD) Flame photometric (FPD), Nitrogen phosphorous (NPD), and Mass spectrometer (MS) are detectors that are used in gas chromatography.
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