Gas chromatography

1. hassan-alnajem
Gas chromatography (GC)
By : Hassan ALNAJEM
Alnajemhassan@gmail.com

2. Gas chromatography (GC)
• Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for
separating and analyzing compounds that can be vaporized without decomposition.
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3. GC
• We used in analytical chemistry for separating and analyzing compounds that can be vaporized without
decomposition.
For example : we use to check additives
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4. GC Process
A gas chromatograph consists of a flowing mobile phase, an injection port, a separation column
containing the stationary phase, a detector, and a data recording system A sample is introduce
d into a heated injector, carried through a separating column by an carrier gas, and detected as a
series of peaks on a recorder when components leave the column. Selection of injection port,
column , detector, Temperature & pressure profiles play important role in analysis of sample by
gas chromatography.
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5. Carrier (Mobile phase) Gas Cylinder.
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Mobile phases are generally gases such as Helium, Hydrogen, or nitrogen.
The mobile phase or carrier gas flows through the instrument from a pressurized cylinder.
Carrier gas must by chemically inert with the components of analysis. Carrier gas from cylinder
are passed to GC I nst from Molecular sieve & silica bed to avoid any moisture carryover.
Gasses are stored in cylinders fitted with Pressure regulators to supply the gas to the instrument
at the set pressure. The cylinders are mostly kept outside the Lab (Analysis area) for safety
purposes and the gasses are passed to the gas chromatograph instrument through stainless steel
tubing/conduits.

6. Carrier Gas pressure (flow) Regulator
Flow rate of carrier gas is first controlled by a two stage regulator fitted on the
gas cylinder. Flow control of carrier is also controlled by additional controls
within the instrument The pressure / flow rate gas regulator consists essentially
of two gauge displaying Cylinder pressure & discharge pressure. Discharge
pressure /flow rate of carrier gas is controlled /set by pressure control knob.
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7. Injection Port
The sample injector is a very critical part of the chromatographic equipment and needs to be well
designed and well maintained. The precision and accuracy of a GC analysis will only be as good
as that provided by the sample injector
The sample is injected by a hypodermic syringe, through a silicone rubber septum into the injecti
on port. Sample injected, gets vaporized, & carriers gas coming in injection port carries vaporize
d sample in to the column. Temperature of injection port is kept above the Boling point of all the
components.
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8. Oven
Oven is used to heat the column at set temperatures . Oven also control the temperature
of column as indicated by the micro processor of the Instrument by help of exhaust fan.
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Oven

9. Column ( Stationary phase)
There are two types of columns in common use in GC, and they are the packed column and the o
pen tubular column (capillary column).
The sample is injected into the mobile phase stream just before the front of the column. The colu
mn is designed to produce the separation of different components. Separation is achieved by pro
per selection of the column (Type of column, column dimensions) & temperature profile of the
column.
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10. PACKED COLUMN
Packed Columns
These columns are fabricated from glass, stainless steel, copper, or other suitable tubes.
Stainless steel is the most common tubing used with internal diameters from 1-4 mm. T
he column is packed with finely divided particles (<100-300 mm diameter), which is co
ated with stationary phase. glass tubes are also used for large-scale separations.
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11. CAPILLARY COLUMN
capillary columns are finding broad applications. These are mainly of two types:
Wall Coated Open Tubular (WCOT)
Internal wall of capillary is coated with a very fine film of liquid stationary phase.
Surface Coated Open Tubular (SCOT)
Capillary tube wall is lined with a thin layer of solid support on to which liquid phase is adsorbed.
The separation efficiency of SCOT columns is more than WCOT columns because of increased
surface area of the stationary phase coating.
Fused Silica Open Tubular (FSOT)
Walls of capillary fused silica tubes are strengthened by a polyimide coating. These are flexible
and can be wound into coils.
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12. Type of Column:
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13. Detector
Components separated by column elutes to detector , where it is detected in dimension of space & time. There are many typ
es of detector based on applications. Detector used in analysis of additives is Flame Ionization detector (FID). In FID, compo
nents (in volatile form) gets ionized by Hydrogen & Air flame. Each component of the mixture reaches the detector at a diff
erent time and produces a signal at a characteristic time called a retention time (Rt).
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Flame Ionization Detector

14. Type of Detector :
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15. Control & Date recording
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Goniometers
The detector response is sent to a computer system where the progress of the sample is mon
itored on the computer monitor in graphical form that displays detector response as a
function of run time & milli volts. Main function of Computer are data acquisition & proces
sing. Temperature & Pressure controls are also set by computer controls.

16. hassan-alnajem
Thank you
By : Hassan ALNAJEM
Alnajemhassan@gmail.com