GAS LIQUID CHROMATOGRAPHY

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GAS LIQUID CHROMATOGRAPHY
Principles Partition of molecules between gas
(mobile phase) and liquid (stationary phase).
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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)
• Methylester of fatty acids
• DEGS (diethylene glycol succinate)

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Gas Chromatography
Filters/Traps
Data system
Syringe/Sampler
Regulators
Inlets
Detectors

• gas system
• inlet
• column
• detector
• data system

Column
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Schematic Diagram of Gas Chromatography
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Schematic Diagram of Gas Chromatography
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DETECTORS
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.
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Schematic Diagram of Flame Ionization Detector
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Schematic Diagram of Flame Ionization Detector
Collector
Detector electronics
? - 220 volts
Flame
Chassis ground
Jet
Signal output
Column
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Thermal Conductivity Detector Measures the
changes of thermal conductivity due to the sample
(mg). Sample can be recovered.  
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Thermal Conductivity Detector
Principal The thermal balance of a heated
filament Electrical power is converted to heat
in a resistant 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
and by conduction to the molecules coming into
contact with it.
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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.


Flow
Flow

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Thermal Conductivity Detector
When a compound elutes, the thermal conductivity
of the gaseous mixture of carrier gas and
compound gas is lowered, and the filament in the
sample column becomes hotter than the other
control column. Its resistance increased, and
this imbalance between control and sample
filament resistances is measured by a simple
gadget and a signal is recorded
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Thermal Conductivity Detector
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Relative Thermal Conductivity
Compound Relative Thermal Conductivity
Carbon Tetrachloride 0.05
Benzene 0.11
Hexane 0.12
Argon 0.12
Methanol 0.13
Nitrogen 0.17
Helium 1.00
Hydrogen 1.28
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Thermal Conductivity Detector

• Responds to all compounds
• Adequate sensitivity for many compounds
• Good linear range of signal
• Simple construction
• Signal quite stable provided carrier gas glow
  rate, block temperature, and filament
  power are controlled
• Nondestructive detection

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Electron Capture Detector
For pesticide analysis (picogram). Accept
electrons of carrier gas.
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Electron Capture Detector
ECD detects ions in the exiting from the gas
chromatographic column by the anode
electrode. 3H or 63Ni which emits ?
particles. Ionization N2 (Nitrogen carrier gas)
? (e) N2 2e These N2 establish a base
line X (F, Cl and Br) containing sample ?
(e) ? X- Ion recombination X- N2 X
N2 The base line will decrease and this
decrease constitutes the signal. Insecticides,
pesticides, vinyl chloride, and fluorocarbons
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Electron Capture Detector
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Electron Capture Detector
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Gas Chromatography Application
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SEMI- QUANTITATIVE ANALYSIS OF FATTY ACIDS
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TENTATIVE IDENTIFICATION OF UNKNOWN COMPOUNDS
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Retention Times
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GLC ADVANTAGES
1. Very good separation 2. Time (analysis is
short) 3. Small sample is needed - ml 4. Good
detection system 5. Quantitatively analyzed
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DISADVANTAGES OF GAS CHROMATOGRAPHY
Material has to be volatilized at 250C without
decomposition.
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Gas Chromatogram of Methyl Esters of Fatty Acids
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The Effects of OH groups of Carbohydrates
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Derivation of Glucose with Trimethylchlorosilane

Glucose
Trimethylchlorosilane

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CH
O-Si(CH3)3
2
O
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5HCl

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1
O-Si(CH3)3
(CH3)3-Si-O
O-Si(CH3)3
2
3
O-Si(CH3)3
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Effects of Derivation
1. Time consumption 2. Side reaction 3. Loss of
sample
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THIN LAYER CHROMATOGRAPHY
Stationary Phase ---------gt Silica
Gel Mobile Phase -------------gt Solvent
(developing)
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THIN LAYER CHROMATOGRAPHY
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Thermal Conductivity Detector
The detector contains two filaments one exposed
only to carrier gas, while the other is exposed
to the carrier gas for sample analysis. When the
gas for the sample analysis is only carrier gas ,
the two filaments can be balanced. Instead of a
direct measurement of filament temperature, the
filament resistant, which is a function of
temperature, is measured.
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Thermal Conductivity Detector
The ability of a colliding molecule to carry off
heat depending on its thermal conductivity.
Hydrogen and helium have high thermal
conductivity and therefore will be more efficient
at cooling a heated filament than other gases
will
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Thermal Conductivity Detector
The TCD will respond to any substance different
from the carrier gas as long as its
concentration is sufficiently high enough.
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Thermal Conductivity Detector
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Thermal Conductivity Detector
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Electron Capture Detector
Electron capture compound, X (highly
electonegative element), tends to capture free
electrons and increase the amount to ion
recombination X (F, Cl and Br) e ? X- Ion
recombination X- N2 X N2 The
current will decrease and this decrease
constitutes the signal. Halogens, lead,
phosphorous, nitro groups, silicone and
polynuclear aromatics. Insecticides, pesticides,
vinyl chloride, and fluorocarbons
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Electron Capture Detector