What is Gas Chromatography or GC/GLC?

Gas Chromatography or Gas Liquid Chromatography is a technique applied for separation, identification and quantification of components of a mixture of organic compounds by selective partitioning between the stationary phase and mobile phase inside a column followed by sequential elution of separated components. The technique is suitable for separation of compounds having following characteristics :

  • High volatility
  • Thermal stability
  • Low molecular weights
Gas Purification System

Gas Chromatograph

Why not start with a short video?

In case you are new to Gas Chromatography simply spend about 2 to 3 min on the introductory video on what constitutes a GC system.

Glossary of GC terms

The glossary will help you familiarize with the terminology in case you are not already familiar with the technique

Stationary Phase A solid phase which absorbs the sample components and later releases them in a sequential manner
Mobile Phase A stream of carrier gas used for transporting sample from injection port to the column to the detector
Column Oven A compartment inside which the column is mounted. It maintains a constant temperature or a varying temperature in response to a set temperature programme.
DetectorA device which gives the signal response in terms of area counts under a peak
Column Efficiency Expressed in terms of HETP expresses the resolving power of the GC column
Packed Column A steel or glass tube wound as a coil which holds the stationary phase
Capillary ColumnA fused silica capillary column that holds the liquid absorbent on the tube on its walls
Autosampler A device capable of holding several samples, standard vials and automatically injects a predetermined sample volume into the gas chromatograph
InjectorManual or automated device for precise sample volume introduction
FID Flame Ionisation detector which responds to most organic compounds
TCDThermal Conductivity detector. Universal and nondestructive detector
ECDElectron Capture detector. For compounds containing electronegative elements such as halogens
NPDNitrogen Phosphorus detector. Specific for compounds containing nitrogen or phosphorus
FPDFlame photometric detector.Specific for sulphur and phosphorus containing compounds
MSD Mass Selective detector
GC – MS Hyphenated technique using a combination of GC and Maas spectrometer
FrontingDistortion of peak where the peak front appears distorted
Peak TailingDistortion of peak where the tailing end of the peak appears distorted
Heart CuttingA method which employs two columns of different selectivity. A selected portion of effluent from first column is passed to the second column
Temperature Programming Changing temperature of column oven in a predetermined manner using a program
Retention TimeTime between injection and the maximum of the peak response
SyringeHand held device capable of injecting selected volume into the chromatograph
HETPHeight Equivalent to a theoretical plate. It is a measure of column efficiency and is expressed as an numerical value without units

H = L/N

The larger the number of theoretical plates the lower is HETP and better is the column efficiency
SeptaRubber or silicone discs which are used inside the injector for introduction of sample into the chromatographic system. The syringe needle penetrates this disc at the time of sample injection
FerruleA plug made from graphite or grass for holding the column gas tight into the oven
Gas RegulatorDevice comprising of a controller to record and control pressure in the gas line and also monitor the pressure inside the cylinder
Gas Filter A wall mounted assembly comprising of packed cartridges capable of removing moisture, hydrocarbons, oxygen and other impurities from the inlet gases
PLOT Porous Layer Open Tubular column where an absorbent is bonded to the inner surface of the column. Useful for analysis of permanent gases or high volatility liquids.
SCOTSupport Coated Open Tubular column. A liquid stationary phase is supported on a solid support which is coated to the inner surface of the capillary common.
Split Injection Injection mode where a portion of the vaporized sample is vented out and only a small portion enters the column head. This is used for highly concentrated samples
Splitless Injection Sample injection where purge valve is closed and the entire sample enters the column. The purge valve is then opened to flush the injector
WCOTWall Coated Open Tubular column. The stationary phase is bonded to the inside wall of the capillary column
On-Column Injection The syringe needle enters and delivers the sample onto the top of the column head
Leak test A process to establish that all connections are leak free
Pre-vent A design of sample inlet that splits the injected sample and vents out a portion. The residual portion is only directed to the column. This is suitable when samples are highly concentrated
Refresh your basic skills by registering for the free e-course on GC which will provide you an introduction to the technique and even prepare you for an interview if you are applying for a job in a laboratory equipped with a GC system.

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Want to read all the AAS free course modules right now? Here are all links to all the modules for you!
  1. Module 1 : Introduction to Gas Chromatography Course and its Objectives
  2. Module 2 : Evolution of Gas Chromatography
  3.  Module 3 : Introduction to Gas Chromatography and Its Parts
  4. Module 4 : Role of Gases in Gas Chromatography
  5. Module 5 : Types of Gas Chromatography Injectors
  6. Module 6 : Types of Gas Chromatography Columns
  7. Module 7 : Types of Stationary Phases
  8. Module 8 : Types of Gas Chromatography Detectors
  9. Module 9 : Gas Chromatography Applications
  10. Module 10 : Top 10 Interview Questions on Gas Chromatography

Library of Published Articles

See the list of published articles related to GC specially prepared for upgradation of your laboratory skills and bring about exposure to new concepts and developments. You willl find that the list is ever growing with inclusion of new published articles as and when they are published.

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