Gas Chromatography (GC)

Hashim and Mohd DanielDepartment of Chemistry, Faculty of Science

Universiti Teknologi Malaysia81310 Skudai, Johor, Malaysia

marsin@kimia.fs.utm.my

Department of Chemistry, Faculty of Science Universiti Teknologi Malaysia

______________________________

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