Gas Chromatography (GC)

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Gas Chromatography (GC)
Department of Chemistry, Faculty of Science
Universiti Teknologi Malaysia ____________________
__________ Analytical Chemistry Course

• Hashim and Mohd Daniel
• Department of Chemistry, Faculty of Science
  Universiti Teknologi Malaysia
• 81310 Skudai, Johor, Malaysia

marsin_at_kimia.fs.utm.my
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Outline

• Introduction to GC
• Instrumentation
• Injector
• Oven
• Columns
• Applications

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Gas Chromatographic equipment
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GC

• Gas chromatography is a chromatographic technique
  that uses a gas as the mobile phase and either a
  liquid or solid as the stationary phase.
• The analytes are adsorbed or dissolved in the
  stationary phase due to an equilibrium based on
  the vapor pressure and other additional
  interactive forces.
• The mobile phase in GC is referred to as the
  carrier gas because ther is little interaction
  between the analyte and the gas phase.
• Gas-solid chromatography (GSC) uses a solid
  stationary phase while gas-liquid chromatography
  (GLC) uses a liquid stationary phase that is
  bonded or coated onto a solid support.

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GC Instrument
  A schematic diagram of a capillary gas
chromatograph.

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GC Instrument
  A schematic diagram of a gas chromatograph.

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GC Instrument

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Gases for GC
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Split/splitless injector for GC
Rajah 6.2 Gambarajah skema sejenis peranti untuk
penyuntikan berpecah. Peranti ini juga boleh
digunakan untuk penyuntikan tidak berpecah dengan
pengawalan injap-injap berkenaan.
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Oven temperature
Rajah 6.3 Contoh kitar suhu teraturcara bagi
ketuhar kromatografi gas.
Suhu isoterma
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Isothermal vs temperature-programmed GC
Rajah 6.4 Pemisahan GC sebatian-sebatian
n-alkana menggunakan turus HP-101
(metilpolisiloksana), 50 m x 0.32 mm I.D.,
ketebalan 0.3 ?m. (a) GC isoterma pada 140 oC.
(b) GC suhu teraturcara 50 - 230 oC dengan kadar
4 oC minit?1.
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GC Columns and stationary phases

• Heart of the chromatographic system
• Determine efficiency and selectivity

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GC columns packed vs open tubular
 Rajah 6.5 Gambarajah skema turus terpadat dan
turus tiub terbuka rerambut tipikal.
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Packed columns

• Three components
• Column tubing
• Support material
• Liquid stationary phase

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Column tubing

• Criteria
• Inert, thermally stable, coil up
• Types
• Copper, stainless steel, glass
• Typical sizes
• 1-3 m long, 1/16, 1/8,1/4 inch OD, 2-3 mm ID
• Inner surface silylated
• To reduce interaction with polar analytes

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Packing materials
Rajah 6.7 Gambarajah skema menggambarkan
keratan rentas contoh padatan yang terdiri
daripada bahan penyokong yang tersalut dengan
fasa cecair.
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Support materials

• Criteria
• Unreactive towards analyte and liquid phase,
  uniform particles and pore size
• Diatomaceous earths Chromosorb
• Particle sizes
• Analytical column 80-100, 100-120 mesh
• Preparatory column 40-60, 60-80 mesh
• Chemical treatment
• AW removes metallic impurities
• AW-DMCS remove silanol groups

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Examples of GC support materials
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E.g.GC packing materials
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Non-diatomite support materials
Porous Polymers - Porapak Polymers
Chromosorb 101 (PSDVB), 103
(PS) Tenax Polymers - 2,6-diphenyl-p-pheny
lene oxide Carbopacks support - Inertness can be
manipulated Adsorbents - Molecular
sieve Silica gel - inertness can be
manipulated Carbon molecular sieves
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Open tubular columns

• No support material
• Liquid phase coated on wall of column (WCOT)
• Flexible fused silica
• Coated with polyimide layer
• Temp. lt 350oC or else coating pyrolysed
• ID 0.1 0.75 mm
• Film thickness 0.1 5 ?m
• Column length 5-50 m
• As ID and film thickness ?, sample capacity ?,
• but efficiency ?
• Typical analytical column 25 m x 0.22 mm x 0.25
  ?m

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Liquid phase requirements

• High solubility
• Differential solubility (high ?)
• Low vapour pressure (maximum
• temperature)
• Low viscosity (minimum temperature)
• 10 vs. 5 more plates, but 2 x tR
• Use light loading (3) for high boilers
• Use heavy loadings (20) for gases

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Non-polar liquid phases in GLC

• Hydrocarbon phases Squalane (C30H62), Apolene
  (C87 hydrocarbon), Apiezon L(-(CH2)n-)
• - Separation of non-polar molecules
  n-alkanes
• Alkylsilicone liquid phases SE-30, OV-1,
  OV-101
• Dimethylsilicone (-(-Si(Me)2-O-)- polymer)
• BP-1, Ultra-1, DB-1

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GC on non-polar liquid phases
230 C
2 C/min
50 C
Hydrocarbons
Essential oil (Cymbopogon nardus)
Column Ultra 1, 30 m x 0.25 mm x 0.25 mm
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Polar liquid phases in GLC

• Substituted silicone liquid phases
• methylphenyl silicone
• - OV-105, CP-Sil 58
• Ester liquid phases
• - Poly(diethylene glycol adipate) DEGA
• - Poly(diethylene glycol succinate) DEGS
• Polyether liquid phases
• Carbowax 200 to Carbowax 20M
• (Polyethylene glycol, PEG)
• - HP20-M, BP-Wax, BP20

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GC on polar liquid phase
230 C
Hydrocarbons
4 C/min
50 C
Essential oil (Cymbopogon nardus)
Column HP-20M (Carbowax 20M)
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Other phases

• Free fatty acid phase (FFAP) or
• Carbowax 20M impregnated with
• terephthalic acid (Carbowax 20M-TPA)
• - Separation of free carboxylic acids C1
  to C7

• Chiral liquid phases with amino acid
• derived centers
• Separation of enantiomers
• - Chirasil-L-Val, Chirasil-D-Val
• - ?-Dex, ?-Dex, ?-Dex

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Liquid stationary phases
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Liquid stationary phases and applications
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Gas-solid chromatography
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Porous polymer phases
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Porous polymer phases
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Factors in selecting stationary phase

• Nature of analyte
• Stationary phase type
• Column internal diameter
• Film thickness
• Column length

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Packed vs Open tubular columns
Factor Packed Column Open Tubular
Efficiency low to moderate high
Sensitivity low high
Operation easy less easy
Sample amount large small
Price low high
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Effect of column internal diameter (ID)
Open Tubular
Packed Column
Characteristics Column ID 2 mm 0.20 mm 0.32 mm 0.75 mm
Sample capacity(each component) 20,000 ng 5.30 ng 400 500 ng 10,000 15,000 ng
EfficiencyTheoretical plates, n 2000 5000 3000 1170
Optimum flow rate(mL/min) 20 0.4 1.4 5.0
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Column conditioning

• Condition at
• A. 20 oC higher than analysis temp
• B. at least 10-20 oC less than stated max.
  operational temp of phase
• Never condition at columns max temp
• Program temp slowly to conditioning temp (2-4
  oC/min)
• Cool down slowly (nonbonded phase)
• Purge column with carrier gas for 1/2 hr before
  heating over
• Very high carrier gas flows can be used for
  conditioning
• Conditioning time varies with your need

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GC Applications

• Petrochemical
• Environmental
• Pharmaceutical
• Oleochemical
• Others

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Thank you