Gas Chromatography (GC)
Hashim and Mohd DanielDepartment of Chemistry, Faculty of Science
Universiti Teknologi Malaysia81310 Skudai, Johor, Malaysia
Department of Chemistry, Faculty of Science Universiti Teknologi Malaysia
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Analytical Chemistry Course
Introduction to GC Instrumentation Injector Oven Columns Applications
Outline
Gas Chromatographic equipment
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.
GC
GC Instrument
A schematic diagram of a capillary gas chromatograph.
Integrator/Plotter
Injector DetectorPressure regulator
Carrier gas
Column
Oven
Valve Work Station
GC Instrument
A schematic diagram of a gas chromatograph.
Integrator/Plotter or Work Station
Injector DetectorTwo-stage regulator
Carrier gas
Column
Oven
GC Instrument
Gases for GC
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.
Gas pembawa
Ferul grafit
Penutup septum
Turus rerambut
Laluan
septumpembersih
Laluankeluar
Liner
PemanasInjap
Septum
Oven temperature
Rajah 6.3 Contoh kitar suhu teraturcara bagi ketuhar kromatografi gas.
Permulaan
SuntikCerun I
Menanti
Cerun II
Akhir
Suhu
Masa
Bersedia
Suntik
Penyejukan
Permulaan
SuntikCerun I
Menanti
Cerun II
Akhir
Suhu
Masa
Bersedia
Suntik
Penyejukan
Suhu isoterma
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 minit1.
C12
C14
C16
C10C8
C8 C10 C12 C14 C16 C18
C20
0 20 40 min
0 20 min
GC Columns and stationary phases
Heart of the chromatographic system
Determine efficiency and selectivity
GC columns: packed vs open tubular
Rajah 6.5 Gambarajah skema turus terpadat dan turus tiub terbuka rerambut tipikal.
4 mm I.D.
0.2 mm I.D.
Turus silika
Lapisan poliimida
Lapisan fasa cecair
Turus terpadat
Turus tiub terbuka(jenis WCOT)
Packed columns
Three components Column tubing Support material Liquid stationary phase
Column tubing
CriteriaInert, thermally stable, coil up
TypesCopper, stainless steel, glass
Typical sizes1-3 m long, 1/16, 1/8,1/4 inch OD, 2-3 mm ID
Inner surface silylatedTo reduce interaction with polar analytes
Packing materials
Rajah 6.7 Gambarajah skema menggambarkan keratan rentas contoh padatan yang terdiri daripada bahan penyokong yang tersalut dengan fasa cecair.
Penyokongpepejal Tapak aktif
Fasa cecair
100 m
SiSi Si OO
OH OH OH
Diatomite supportsurface
Support materials
CriteriaUnreactive towards analyte and liquid phase, uniform particles and pore size
Diatomaceous earths – ChromosorbParticle sizes
Analytical column: 80-100, 100-120 meshPreparatory column: 40-60, 60-80 mesh
Chemical treatmentAW – removes metallic impuritiesAW-DMCS – remove silanol groups
Examples of GC support materials
E.g.GC packing materials
Non-diatomite support materials
Porous Polymers - Porapak Polymers
Chromosorb 101 (PSDVB), 103 (PS)
Tenax Polymers - 2,6-diphenyl-p-phenylene oxide
Carbopacks support - Inertness can be manipulated
Adsorbents - Molecular sieve
Silica gel - inertness can be manipulated
Carbon molecular sieves
Open tubular columns
No support material Liquid phase coated on wall of column (WCOT) Flexible fused silica
Coated with polyimide layerTemp. < 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
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
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
GC on non-polar liquid phases
50 °C
230 °C
2 °C/minHydrocarbons
Essential oil(Cymbopogonnardus)
Column: Ultra 1, 30 m x 0.25 mm x 0.25 mm
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
GC on polar liquid phase
50 °C
230 °C
4 °C/min Hydrocarbons
Essential oil(Cymbopogonnardus)
Column: HP-20M (Carbowax 20M)
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
Liquid stationary phases
Liquid stationary phases and applications
Gas-solid chromatography
Porous polymer phases
Porous polymer phases
Factors in selecting stationary phase
Nature of analyte Stationary phase type Column internal diameter Film thickness Column length
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
Effect of column internal diameter (ID)
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
Open TubularPacked Column
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 column’s 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
Petrochemical Environmental Pharmaceutical Oleochemical Others
GC Applications
Thank you
