lecture 10 - gas chromatography
DESCRIPTION
About gas chromatography by Dr. Kesaven from UMTTRANSCRIPT
GAS
CHROMATOGRAPHY
MMS 3201
AQUATIC METHODOLOGY AND
INSTRUMENTATION
Izwandy Idris, Blue Cabin,
ext. 3467, [email protected]
Introduction What is Chromatography?
Separation of compounds (solutes) into separate
components for identification (qualitative) and
concentration determination (quantitative)
Several techniques including such as Thin Layer,
Size-exclusion, HPL and Gas Chromatographies.
Gas chromatography – separating and analysing
volatile compounds that can be vaporized without
decomposition
GAS CHROMATOGRAPHY
Suitable for volatile and thermally stable (<450 oC) compound
Application in aquatic science: detection of Disinfection by-Products, taste odour components, insecticides, pesticides, hydrocarbon, fatty acids etc.
Sample of organic compounds is injected into an inert gaseous mobile phase (known as the carrier gas) for analysis.
The sample is carried through a packed or capillary column and the components in the sample are separated based on their ability to distribute between the stationary phase and the mobile phase.
GC analytical technique
2. Separation processes
i. Different adsorption with column packing
materials.
ii. Different Boiling point (Temp programming
System).
iii. Different in weight (Molecular weight)
A B C
The boiling points for
A=70oC B=100oC & C= 150oC.
If we increase the column temperature
from 60oC to 200oC at the rate of
10oC/min, the results of the
chromatogram will be
Peak
height
Time, min.
A B C
Carrier (inert) gas
Sample injected
(A, B &C)
Initial column temp set at 60oC
Retention Time, RT
INJECTION PORT
GC SEPARATION
Common inert mobile phase – Neon (Ne), Argon (Ar), Helium (He) and Nitrogen gas (N2)
Inert gas – no chemical reaction with mobile phase (compound) and stationary phase.
Chromatography column – two types i.e. packed and capillary
Capillary Columns
A.k.a open tubular column - made from fused silica coated with a protective polymer.
Up to 100 meter, diameter 50 – 300 m.
Types of Columns for GC
TYPES OF GC COLUMN
(0.01 –0.053cm)
(0.3-0.4cm)
Types of Columns for GC
Packed Column
• Made from glass, stainless steel, copper or aluminum, typically 2 – 6 m long, internal diameter 2 – 4 mm.
• Filled up with particulate solid with diameter ranging between 30-350 m. Smaller solid particle, > separation
TYPES OF GC COLUMN
(0.01 –0.053cm)
(0.3-0.4cm)
Comparison Of column
Capillary column Packed column
Capillary Column (Shimadzu 2010)
The Stationary Phase
Use high molecular weight, thermally stable
polymer, and chemically inert
Coating the inner tube (capillary) or solid support material
Solutes with different of boiling points are easily separated. Two solutes with the same boiling points could be separated if the stationary phase reacts with one of the solutes
Optimal detection – similar polarity with solute (increase separation and absorption)
Non-polar solutes – easier separation with non-polar stationary phase
Injection of Sample
1. Sample must be volatile.
2. The analyte must be present at an appropriate concentration.
3. Injected sample must not be degradable in the column.
Temperature Control (Temp Programming)
Important for good separation
Column inside a thermo-stated oven
Isothermal separation – column is
maintained at a constant temperature
Multi separation – temp is set slightly below
the lowest boiling solute and increase
gradually (Temperature programming)
1. Thermal Conductivity Detector
◦ based on mobile phase’s thermal conductivity
◦ Helium is selected mobile phase – high thermal conductivity
◦ When a solute is eluted from the column, the thermal
conductivity of the mobile phase decreases – change in
conductivity
◦ TCD gives a signal for any solute which has different thermal
conductivity from helium
◦ Can be used to detect any compound
DETECTORS FOR GC
2. Flame Ionization Detector (FID)
◦ Combustion of organic compounds in H2/air flame - flame
rich in electrons and ions.
◦ Ions are detected with electrically charge metal detactor (DC:
~300 v), more current across detector – high rate of
ionisation – high concentration
◦ used only for organic compounds
◦ Sensitivity is 2 – 3 lower than the TCD.
DETECTORS FOR GC
3. Electron Capture Detector (ECD)
◦ consists of a beta emitter (electron) such as 63Ni.
◦ Emitting electrons ionize the mobile phase (usually N2), production of additional electrons – electric current
◦ When the eluted solute pass through the ECD, the electric current in the ECD decrease and a signal is obtained
◦ Selective detector for solutes with electronegative functional groups (halogenated compounds and nitrogen groups) – pesticides (environment), pharmaceutical.
DETECTORS FOR GC
/Hydrocarbons
OM
OM
N2
H2 + O2
Example of Chromatogram-Petroleum
Hydrocarbon Analysis
Petroleum hydrocarbons are extracted from sea water and fractionated into
1. Aliphatic hydrocarbon &
2. Aromatic hydrocarbon fractions using
Column Chromatography.
GC-FID with capillary column (30 m) and temperature programming – 20 min (70 oC), increase to 300oC with a rate of 8oC/min and hold at 300 oC for 30 min
Aliphatic Hydrocarbons
min0 10 20 30 40 50 60 70
pA
50
100
150
200
250
FID2 B, (JOHNSON\SIG11155.D) C
8
C9
C10
C16
C17
IS
TD
i C
18
C19
C20
C21 C
22 C
23
C24
C26
C27
C28
C29
C32
Polyaromatic Hydrocarbons
min0 10 20 30 40 50 60 70
pA
20
40
60
80
100
120
FID2 B, (JOHNSON\SIG11026.D)
IS
TD
I
IS
TD
II
Pyr
IS
TD
III
BaA
BkF
BbF
IP
Qualitative & Quantitative Analysis
1. Use Reference Standard Material – such as
EPA 16 Aromatic Hydrocarbons
2. RSM is analyzed with the GC under the
same condition set for the analysis.
3. RT value and the intensity of peak are
recorded
4. Compare with the sample’s peak
Retention Value(RT) – 11.9 minutes
Aliphatic Hydrocarbons External Standard
min0 10 20 30 40 50 60 70
pA
100
200
300
400
500
600
FID2 B, (JOHNSON\SIG11151.D)
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18 C
19
C20
C21
C22
C23 C
24
C25
C26
C27 C
28
C29
C30
C32
Polyaromatic Hydrocarbons External Standard
min0 10 20 30 40 50 60 70
pA
50
100
150
200
250
300
350
400
450
FID2 B, (JOHNSON\SIG11032.D)
Na
Ace
Acy
Flu
Ph
An
FI
Pyr
Chy
rs B
aA
BkF
BbF
BaP IP dB
ahA
Bgh
iP
1. Sample with unknown solutes
2. Effluent from GC is introduced into the mass spectrometer’s ionization chamber – mobile phase removal
3. Ionization chamber – ionization of molecules and separated by mass to charge ratio
4. Selective monitoring detector is used to detect the specific mass-to-charge ratio produced electricity current
GC-MS (Identification of Organic Compounds)
GC MS(Shimadzu 2010)
GC-MS FLOW DIAGRAM
GC – MS 3D VIEW
Gas Chromatograph – Mass Spectrometer
Total Organic Carbon Analyzer
(TOC) Analysis of organic substances in
- Water
- solid including tissues and sediment
IR light absorption
Organic + O2 CO2
Infrared Analysis
600oC
TOC
Video on Gas Chromatography
https://www.youtube.com/watch?v=08YWhLTjlfo