Gas Chromatography

Introduction to Gas Chromatography

Written by Bette Kreuz Produced by Ruth Dusenbery University of Michigan-Dearborn 2000

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, ❚ carried through a separating column by an inert gas, and ❚ detected as a series of peaks on a 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/ Varian 3350 GasComputer Controls for Regulator Chromatograph Method and Output

Slide 3a ❚ Chromatographic separation involves the use of a stationary phase and a mobile phase. phase ❚ Components of a mixture carried in the mobile phase are differentially attracted to the stationary phase and thus move through the stationary phase at different rates. rates

Slide 3 Injector

Flow of Mobile Phase

Detector

T=0

T=10’

T=20’

Most Interaction with Stationary Phase Least

Slide 4a In gas chromatography ❚ the mobile phase is an inert carrier gas and ❚ the stationary phase is a solid or a liquid 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 6 Two Stage Tank Regulator

GC 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 Injector Detector

Column in Oven

Slide 9a ❚ Preprogrammed parameters, called a separation method, method control the operation of the system.

Slide 9 Control 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 µ l Syringe

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 Column installed in Oven Compartment.

Enter from Injector

Exit to Detector

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 time. time ❚ The area under a peak is related to the amount 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 peaks correlates with the number of components in the sample, the area under each peak correlates with the relative amount of that component in the sample,

Slide 16