Download - Gas Chromatography
Introduction to Gas Chromatography
Written by Bette KreuzProduced by Ruth Dusenbery
University of Michigan-Dearborn2000
Introduction
Gas chromatography is an instrumental method for the separation and identification of chemical compounds.
Slide 1a
A sample is introduced into a heated injector,heated injector, carried through a separating columnseparating column by
an inert gas, andinert gas, anddetecteddetected as a series of peaks on a as a series of peaks on a
recorder recorder when components leave the column.
Slide 1
Slide 2a
The instrument used for our experiments, a Varian 3350 gas chromatograph, is shown here.
Slide 2
Carrier gas/Carrier gas/RegulatorRegulator
Varian 3350 Gas Varian 3350 Gas ChromatographChromatograph
Computer Controls forComputer Controls forMethod and OutputMethod and Output
Slide 3a
Chromatographic separation involves the use of a stationary phasestationary phase and a mobile phasemobile phase.
Components of a mixture carried in the mobile phase are differentially differentially attracted to the stationary phaseattracted to the stationary phase and thus move through the stationary move through the stationary phase at different ratesphase at different rates.
Slide 3
T=0
T=10’
T=20’
InjectorInjector DetectorDetector
MostMost Interaction with Stationary Phase Interaction with Stationary Phase LeastLeast
Flow of Mobile PhaseFlow of Mobile Phase
Slide 4a
In gas chromatography
the mobile phasemobile phase is an inert carrier inert carrier gasgas and
the stationary phasestationary phase is a solidsolid or a liquid coated on a solidliquid coated on a solid contained in a coiled column.
Slide 4
Slide 5a
Columns can be short, large diameter packed column or long, very small diameter capillary columns.
Each has its own use and associated advantages and disadvantages.
Slide 5
Slide 6a
The mobile phase or carrier gas flows through the instrument from a pressurized tank.
Flow rate is controlled by a two stage regulator on the gas tank and additional controls within the instrument.
Slide 6Two Stage Two Stage
Tank RegulatorTank RegulatorGC Flow ControllerGC Flow Controller
Slide 7a
The column is contained in a heated oven that is preceded by a heated injector port and followed by a heated detector unit which produces the output.
A set of preprogrammed parameters regulate the operation of the system.
Slide 7
Slide 8a
The injector, column oven and detector components of the Varian 3350 gas chromatograph are shown here.
Slide 8
InjectorInjector DetectorDetector
Column in OvenColumn in Oven
Slide 9a
Preprogrammed parameters, called a separationseparation methodmethod, control the operation of the system.
Slide 9
Control Panel sets Separation MethodControl Panel sets Separation Method
Slide 10a
Samples may be pure compounds.
However, they are often prepared as dilute solutions due to the sensitivity of the detection methods.
Slide 10
Dilute Solution
Pure Sample
Slide 11a
When the system is ready, as indicated by the ready light, samples are injected into the injector port where they are vaporized and carried into the column by the carrier gas.
Slide 11
10 10 llSyringeSyringe
Slide 12a
Separation of the components of the mixture occurs in the column.
Compounds differentially retained in the stationary phase reach the detector at different times to produce a set of peaks along the time line.
Slide 12
Packed ColumnPacked Columninstalled in Oven installed in Oven Compartment.Compartment.
Exit to Exit to DetectorDetector
Enter Enter fromfrom
InjectorInjector
Slide 13a
The detector response is sent to a computer system where the progress of the sample is monitored on the computer monitor in graphical form that displays detector response as a function of run time.
Slide 13
Slide 14a
Each component of the mixture reaches the detector at a different time and produces a signal at a characteristic time called a retention timeretention time.
The area under a peakarea under a peak is related to the amount of that componentamount of that component present in the mixture.
Slide 14
Slide 15a
The detector information can also sent to a printer that produces hard copy of the chromatographic run.
Slide 15
Slide 16a
In the printout of the chromatographic analysis:
the number of peaksnumber of peaks correlates with the numbernumberof componentsof components in the sample,
the area under each peakarea under each peak correlates with the relative amount of that componentrelative amount of that component in the sample,
and if standard information is available, theretention timeretention time under defined conditions can be used to identifyidentify each component.
Slide 16