Thank you for the informative presentation on gas chromatography. Here are a few comments:
- The level of technical detail provided on the various components and detectors is very useful for understanding how GC works. The diagrams help visualize the processes.
- Covering common stationary phases, applications like fatty acid analysis, and qualitative/quantitative analysis techniques provides a good overview of GC capabilities.
- Discussing limitations like sample volatility and potential decomposition is important context. Derivatization methods to overcome this are nicely explained.
- Effects of sample derivation like increased time and potential side reactions/loss are good to note. Overall it seems a well-rounded introduction to GC principles and applications. The presentation style and organization of content helps explain
2. • Principles
Partition of molecules between gas (mobile
phase) and liquid (stationary phase).
Gas Liquid Chromatography
3. Most Common Stationary Phases
1. Separation of mixture of polar compounds
Carbowax 20M (polyethylene glycol)
2. Separation of mixtures of non-polar compounds
OV101 or SE-30 (polymer of methylsilicone)
3. Methylester of fatty acids
DEGS (diethylene glycol succinate)
6. Detector
• Flame Ionization Detector (Nanogram - ng)
High temperature of hydrogen flame (H2
+O2
+ N2
)
ionizes compounds eluted from column into flame.
The ions collected on collector or electrode and were
recorded on recorder due to electric current.
8. Measures the changes of thermal conductivity due
to the sample (µg). Sample can be recovered.
Thermal Conductivity Detector
9. Thermal Conductivity Detector
Principal: The thermal balance of a heated filament
Electrical power is converted to heat in a filament and
the temperature will climb until heat power loss form
the filament equals the electrical power input.
The filament may loose heat by radiation to a cooler
surface by conduction to the molecules which contact
with the filament.
10. Thermal Conductivity Basics
When the carrier gas is contaminated by
sample , the cooling effect of the
gas changes. The difference in cooling
is used to generate the detector signal.
The TCD is a nondestructive,
concentration sensing detector. A
heated filament is cooled by the flow of
carrier gas.
Flow
Flow
11. When a separated compound elutes from the
column , the thermal conductivity of the mixture
of carrier gas and compound gas is lowered. The
filament in the sample column becomes hotter
than the control column.
The imbalance between control and sample
filament temeprature is measured by a simple
gadget and a signal is recorded
Thermal Conductivity Detector
14. • Responds to all compounds
• Adequate sensitivity for many compounds
• Good linear range of signal
• Simple construction
• Signal quite stable if carrier gas glow rate, block
temperature, and filament power are effectively controlled
• Nondestructive detection
Thermal Conductivity Detector
15. Electron Capture Detector
Analyses for pesticide, Insecticides, vinyl
chloride, and fluorocarbons in foods.
Most sensitive detector (10-12
gram)
16. Electron Capture Detector
ECD detects positive ions of carrier gas by the anode electrode.
63
Ni emits β particles.
Ionization : N2 (Carrier gas) + β (e) = N2
+
+ 2e. The N2
+
establish a
“base line”
X (F, Cl and Br) containing sample + β (e) X-
Ion recombination: X-
+ N2
+
= X + N2, The “base line” due to the
N2
+
will decrease and this decrease constitutes the signal.
The more the halogen containing X compounds in the sample, the
less the N2
+
in the detector
22. Semi-Quantitative Analysis of Fatty Acids
C
C
C
DetectorResponse
Retention Time
14
16
18
PeakArea
Sample Concentration (mg/ml)
2
4
6
8
10
0.5 1.0 1.5 2.0 2.5 3.0
The content % of C fatty acids =
C
C + C + C
100∗
14
181614
= the content % of C fatty acids14
14
23. Tentative Identification of Unknown
Compounds
Response
GC Retention Time on Carbowax-20 (min)
Mixture of known compounds
Hexane
Octane Decane1.6 min = RT
Response
Unknown compound may be Hexane
1.6 min = RT
Retention Time on Carbowax-20 (min)
24. Response
GC Retention Time on SE-30
Unknown compound
RT= 4 min on SE-30
Response
GC Retention Time on SE-30
Hexane
RT= 4.0 min on SE-30
Retention Times
25. Advantages of Gas Chromatography
• Very good separation
• Time (analysis is short)
• Small sample is needed - µl
• Good detection system
• Quantitatively analyzed
26. Disadvantages of Gas Chromatography
Material has to be volatilized at 250C without decomposition.
R C OH CH3OH H2SO4
O
R C O CH3
O
CH2 O C R
CH O C R
CH2 O C R
O
O
O
CH3OH
O
R C O CH3
CH3ONa
Fatty Acids Methylester
Reflux
+ 3
Volatile in Gas
Chromatography
Volatile in Gas
Chromatography
+ +
