chapter 5b gas chromatography department of chemistry, faculty of science universiti teknologi...
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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).