Gas Chromatography

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 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.
Detector	A 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 Column	A 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
Injector	Manual or automated device for precise sample volume introduction
FID	Flame Ionisation detector which responds to most organic compounds
TCD	Thermal Conductivity detector. Universal and nondestructive detector
ECD	Electron Capture detector. For compounds containing electronegative elements such as halogens
NPD	Nitrogen Phosphorus detector. Specific for compounds containing nitrogen or phosphorus
FPD	Flame 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
Fronting	Distortion of peak where the peak front appears distorted
Peak Tailing	Distortion of peak where the tailing end of the peak appears distorted
Heart Cutting	A 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 Time	Time between injection and the maximum of the peak response
Syringe	Hand held device capable of injecting selected volume into the chromatograph
HETP	Height 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
Septa	Rubber 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
Ferrule	A plug made from graphite or grass for holding the column gas tight into the oven
Gas Regulator	Device 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.
SCOT	Support 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
WCOT	Wall 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

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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.