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