Gas chromatography (GC)

Basic of Gas chromatography (GC)

What is gas chromatography?

GC- It is specifically Gas-Liquid Chromatography that comprises a sample being vapourised and injected onto the head of the chromatographic column. 

That transferred to stationary phase (Column) and separated by means of partition coefficient or affinity toward stationary phase and detected over GC Detector.

Origins of Gas Chromatography (Who invented GC?)

  • The development of GC as an analytical technique was founded by Archer J. P. Martin and Richard L. M. Synge around year 1952. It was suggested to use of gas-liquid partition chromatograms for analytical use.
  • Gas chromatography is also known on occasion as vapor-phase chromatography (VPC), or gas-liquid partition chromatography (GLPC).

Related: Handling of HPLC and GC Columns, Theoretical plate numbers (N) and Determination of “N” in Chromatography, Relative Response Factor (RRF)

Gas Chromatography Principle and Instrumentation

1. Principle of Gas chromatography (GC)

  • A gas chromatograph is made of a narrow tube, known as the column, through which the vaporized sample passes, carried along by a continuous flow of inert or non-reactive gas.
  • The vaporised sample goes down a thin tube known as the column, which is carried along by a continuous flow of inert or non-reactive gas in a gas chromatograph.
  • Components of the sample flow through the column at varying rates, so based  on their  chemical  and physical properties and the resulting interactions with the stationary phase, which is the column lining or filling.
  • Compounds with a stronger affinity for the stationary phase spend more time in the column, elute later, and have a longer retention time (Rt) than those with a stronger attraction for the mobile phase.
  • Intermolecular interactions induce affinity for the stationary phase of the sample, and the polarity of the stationary phase can be selected to maximize interaction and consequently separation.
  • The sample is therefore partitioned between the gas and a small layer of a non-volatile liquid maintained on a solid support, resulting in separation.
  • A sample containing the solutes is injected into a heated block, where it is quickly vaporized and swept into the column inlet as a plug of vapor by the carrier gas stream.
  • The stationary phase adsorbs the solutes, which are then desorbed by a fresh carrier gas. A temperature-controlled oven is usually used to encase the column.
  • As the compounds escape the column, they are electronically recognised and identifie
GC Gas Chromatography, Basic of GC, Principle of GC, Available GC in India
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2. Instrumentation of GC (Parts of Gas chromatography)

GC Components consist of below parts,

1. Carrier gas or GC Mobile Phase

  • The carrier gas is injected into the gas chromatograph from a gas cylinder. It flows at a consistent rate through the column and out the detector outlet.
  • The mobile phase in GC, unlike other procedures, does not interact with compounds and mainly serves to transport them. As a result, the carrier gas needs to be inert.
    • Carrier gas in gas chromatography – (H2, He, N2)
    • Make-up gas – (H2, He, N2)
    • Detector Fuel Gas – (H2 & Air, Ar or Ar & CH4, N2) depending on the detector type

2. Sample Injection

  • Depending on the experiment, the sample likely be very different.
  • GC samples are typically made up of non-polar, low-molecular-weight, thermally stable, and vaporizable chemicals.
  • List of Sample Injection Methods:
    • Split Injection Method: The sample is eliminated as only a portion is injected into the column
    • Splitless Injection Method: Not split, but only for 1 to 2 minutes after injection
    • Direct Injection Method: Also known as “Total volume injection”. Sample is not splitted. 
    • Cold Injection Method :
      • A. Cold on-column caps Injection (Cold OCI)
      • B. PTV Injection System (Programmable Temperature Vaporizer)

3. Column/Stationary Phase

  • The column is a coiled tube composed of metal or glass that can resist high temperatures and comes in a variety of lengths and diameters. The stationary phase is found inside the tube.
  • This can be a variety of solid or liquid objects with variable polarity that interact with the chemicals going through.
  • The stationary phase is either a packed column or a wall-coating film (capillary column).

4. Oven

  • GC heated to vaporized material after injection by GC instruments.
  • GC oven keeps the column heated, as a result continue to have gaseous molecules traveling through stationary phase.
  • Oven makes temperature from room temperature (RT) to 300 °C.
  • A temperature programme can be programmed to maintain a constant temperature or progressively increase the temperature (ramping). The programme you choose will be determined by the nature of the sample.

5. GC Detector

  1. Flame ionization (FID)
  2. Thermal conductivity (TCD)
  3. Electron capture (ECD)
  4. Flame thermionic detector (FTD)
  5. Nitrogen-phosphorus
  6. Flame photometric (FPD)
  7. Photo-ionization (PID)
  8. Hall electrolytic conductivity
  9. Barrier Discharge Ionization Detector (BID)
  10. Sulfur chemiluminescence Detector (SCD)

6. GC Chromatogram or reading of GC record

  • Varies available software capture the data from the detector and give the response in the chromatogram.
  • Chromatogram is presented as a plot of Detector response (y-axis) vs. retention time (RT) (x-axis).

Read : Difference Between Isocratic and Gradient Elution

Application of GC (Gas chromatography)

IndustryType of Analysis
PharmaceuticalResidual solvent analysis, Assay, Excipient analysis
Food and beveragesComponent analysis, food safety analysis, halal analysis of alcohol
EnvironmentalAir, water, soil
PetrochemicalsSimulated distillation, component analysis
ChemicalsMaterial, polymer, additive, gas purity analysis, gas emission in automotives
Energy and gasArtifcial photosynthesis research

Available Gas Chromatography Model in India:

  • Gas Chromatograph Manufacturers, Model and Software
Sr. No.GC ModelGC MakeSoftwareRemarks
1Clarus® 590PerkinElmer®ChemDrawNA
2TurboMatrix 650 ATDPerkinElmer®ChemDrawNA
3Scientific ISQ 7610 single quadrupole GC-MS systemThermoScientificChromeleonIntegrated with Mass Spectroscopy. GCMS
4Thermo Scientific TSQ 9610 triple quadrupole GC-MS/MS systemThermoScientificChromeleonIntegrated with Mass Spectroscopy. GCMS
5TRACE™ 1600 Series Gas ChromatographThermoScientific™ChromeleonNA
6Nexis GC-2030
GC-2010 Pro
GC-2014
Tracera GC		Shimadzu, JapanLabSolutionNA
78890 GC System
7890B GC System
8860 GC System		AgilentOpenLabNA
85977B GC/MSDAgilentOpenLab  Integrated with Mass Spectroscopy. GCMS
9CALIDUS™ GCFalcon Analytical Systems & TechnologyNANA

Reference:

https://www.shimadzu.com/an/service-support/technical-support/analysis-basics/fundamentals

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