Transcript ATOMIC ABSORPTION SPECTROSCOPY

Introduction to Gas
Chromatography
Written by Bette Kreuz
Produced by Ruth Dusenbery
University of Michigan-Dearborn
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/
Regulator
Varian 3350 Gas Computer Controls for
Chromatograph Method and Output
Slide 3a
Chromatographic separation involves the
use of a stationary phase and a mobile
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.
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, 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 ml
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.
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,
and if standard information is available, the
retention time under defined conditions can be
used to identify each component.
Slide 16