Chapter 5bGas Chromatography

Department of Chemistry, Faculty of Science Universiti Teknologi Malaysia

______________________________

Analytical Chemistry Course

SSC 1293

Introduction to GC Instrumentation Injector Oven Columns Applications

Outline

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 there 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 equipment

Data handling

Schematic diagram of a capillary gas chromatograph

 .Integrator/Plotter

Injector DetectorPressure regulator

Carrier gas

Column

Oven

Valve Work Station

Column oven

GC Instrument

Gases for GCGas type Flow rate (mL/min)

Carrier gas

N2 or He

• Capillary column 1-2

• Packed Column 40

Detector gases

• Hidrogen 30

• Air 300

Split/splitless injector for GC

Gas pembawa

Ferul grafit

Penutup septum

Turus rerambut

Laluan

septumpembersih

Laluankeluar

Liner

PemanasInjap

Septum

Capillary column

Graphite ferrule

HeaterExitValve

Septum purge

Septum closure

Carrier gas in

Split InjectionSimplest method, ideal if only a limited number of components are present or trace analysis not required.

Injection port fitted with 2 valves, one acting as a septum purge, allowing a small flow of

carrier gas from just below the septum and The second taking carrier gas from the bottom of the

injection port near the column inlet.

In split mode, lower valve is used to adjust the ratio of carrier gas going to waste in the atmosphere compared to flow onto the column.

Typical ratios 10:1 to 50:1 used so that only a small proportion of the sample is transferred onto the column.

Splitless InjectionSuitable for samples containing trace compounds in low conc. – necessary to transfer as much of the sample as possible onto the column to increase sensitivity.Lower valve is closed at time of injection and only a small septum purge flow is used.Injection takes place into heated zone over a period of ~20 s, so that all sample is transferred to the column.After a predetermined period (40-60 s), the lower valve is opened to purge the injection port and to prevent residual sample from causing tailing of the peaks.

Column Oven

For simple samples, separation may be carried out under isothermal conditions of constant temperature.

For samples with wide range of volatility, need to use temperature programming. Enable volatile compound to be resolved at low temperature

and elution of later less-volatile compounds to be speeded up as the temperature increases.

Profile include a series of time events – initial isothermal period, pauses at intermediate fixed temperature, different ramp rates, a final isothermal period and automated cooling-down of column to initial temperature at end of run, ready for the next cycle.

Oven Temperature Programming

Permulaan

SuntikCerun I

Menanti

Cerun II

Akhir

Suhu

Masa

Bersedia

Suntik

Penyejukan

Temp

Time

Cool-down

Ramp 1

Ramp 2Hold

Initial

Inject

Final

Ready

Inject

Isothermal vs temperature-

programmed GC

GC separation of n-alkanes using HP-101 (methylpolysiloxane) column, 50 m x 0.32 mm I.D., 0.3 m thickness. (a) Isothermal GC at 140 oC. (b) Temperature programmed GC 50 - 230 oC at 4 oC min1.

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

4 mm I.D.

0.2 mm I.D.

Turus silika

Lapisan poliimida

Lapisan fasa cecair

Turus terpadat

Turus tiub terbuka(jenis WCOT)

Packed column

Open tubular column

Silica Column

Polyamide layer

Liquid phase layer

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

Schematic diagram showing cross section of packed column comprising of solid support coated with liquid phase.

Penyokongpepejal Tapak aktif

Fasa cecair

100 m

SiSi Si OO

OH OH OH

Diatomite supportsurface

Liquid phase

Active site

Solid support

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 treatmentAcid wash (AW) – removes metallic impuritiesAcid wash and dimethyl dichlorosilane-treated (AW-DMCS) – remove silanol groups

Examples of GC support materialsMaterial Colour Surface (m2/g) Max. liquid

loading (% w/w)Other descriptions

Chromosorb G Grey 0.5 5 For polar samples

Chromosorb W White 1.0 15 For polar samples

Chromosorb P Pink 4.0 30 -

Chromosorb T   7.5 5 Made from Teflon-6, temperature limit 250oC

Chromosorb A   2.7 25 Resembles Chromosorb P, for preparative work

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

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)

Phase (Supelco)

Temp. limits (oC)

Equivalent phases

    Hewlett Packard

Alltech Chrompack

J&W SGE

SBP-1 -60 to 320 HP-1, Ultra-1

AT-1 CP-Sil 5CB

DB-1 BP-1

SPB-5 -60 to 320 HP-5, Ultra-2

AT-5 CP-Sil 8CB

DB-5 BP-5

SPB-1701 Subambient to 280

HP-1701 AT-1701 CP-Sil 19CB

DB -1701

BP-10

SUPELCOWAX 35 to 280 HP-Wax AT-Wax CP-Wax 52 CB

DB-Wax

BP-20

Petrocol 50.2(Petroleum)

-60 to 320 PONA - Squa-lane

- PONA

PTE-5 (Environmental)

-60 to 320 HP-5 MS - - DB-5.625

BPX-625

SPB-608(Pesticides)

Subambient to 300

HP-608 AT-Pesticide

CP-Sil 8CB

DB-608

BP-608

Comparison of Manufacturers’ 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 at1. 20 oC higher than analysis temp2. 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 Forensic Pharmaceutical Oleochemical Others

GC Applications

..

PeakNo.

Components Kovats Index

1 Nonane 900

2 Decane 1000

3 Undecane 1100

4 Naphthalene 1182

5 Dodecane 1200

6 Tridecane 1300

7 1-methyl naphthalene

1322

8 Tetradecane 1400

9 Pentadecane 1500

10 Hexadecane 1600

11 Heptadecane 1700

12 Pristane 1712

13 Octadecane 1800

14 Phytane 1816

15 Nonadecane 1900

16 Cosane 2000

17 Uncosane 2100

18 Docosane 2200

19 Tricosane 2300

20 Tetracosane 2400

GC Profile of Diesel

GC-ECD SEPARATION OF PCB

.GC Conditions: HP-5MS capillary column, Injection port temperature at 280oC and detector temperature at 290 oC. Temperature programming from 200oC (held for 3 minutes) then ramped to 230 oC (held for 3 minutes) at a rate of 5 oC/min and increased to 260 oC (held for 3 minutes) at a rate of 2 oC/min. Peak identity: (1) iso-octane (2) PCB 28, (3) PCB 52, (4) PCB 35, (5) PCB 101, (6) PCB 118, (7) PCB 153, (8) PCB 138 and (9) PCB 180.

GC-ECD SEPARATION OF NITROEXPLOSIVES

Initial oven temperature at 100 oC, held for 2 min then ramped to 250 oC at 15 oC/min and held for 1 minute. The injector temperature and detector temperature at 230 oC and 300 oC. GC column was Ultra 2 (25 m x 0.20 mm ID x 0.11 µm film thickness). helium as carrier gas (1 mL/min) and nitrogen as make-up gas (30 mL/min).