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Chapter 5b Gas Chromatography

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GC-ECD SEPARATION OF PCB GC-ECD SEPARATION OF NITROEXPLOSIVES Chapter 5b Gas Chromatography Outline Introduction to ... 320 HP-5 MS - - DB-5.625 ... 7/21/2003 2:05:56 ... – PowerPoint PPT presentation

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Title: Chapter 5b Gas Chromatography


1
Chapter 5bGas Chromatography
Department of Chemistry, Faculty of Science
Universiti Teknologi Malaysia ____________________
__________ Analytical Chemistry Course SSC 1293
2
Outline
  • Introduction to GC
  • Instrumentation
  • Injector
  • Oven
  • Columns
  • Applications

3
GC
  • 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.

4
GC equipment
Data handling
5
Schematic diagram of a capillary gas chromatograph
Column
oven
 .

6
GC Instrument

7
Gases for GC
  • Gas type Flow rate (mL/min)
  • Carrier gas
  • N2 or He
  • Capillary column 1-2
  • Packed Column 40
  • Detector gases
  • Hidrogen 30
  • Air 300

8
Split/splitless injector for GC
Septum closure
Septum purge
Carrier gas in
Valve
Heater
Exit
Graphite ferrule
Capillary column
9
Split Injection
  • Simplest 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 101 to 501 used so that only a
    small proportion of the sample is transferred
    onto the column.

10
Splitless Injection
  • Suitable 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.

11
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.

12
Oven Temperature Programming
Final
Cool-down
Ramp 2
Temp
Hold
Inject
Inject
Ramp 1
Initial
Ready
Time
13
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 min?1.
14
GC Columns and Stationary Phases
  • Heart of the chromatographic system
  • Determine efficiency and selectivity

15
GC columns packed vs open tubular
Silica Column
Polyamide layer
Packed column
Liquid phase layer
Open tubular column
16
Packed columns
  • Three components
  • Column tubing
  • Support material
  • Liquid stationary phase

17
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

18
Packing materials
Liquid phase
Solid support
Active site
Schematic diagram showing cross section of
packed column comprising of solid support coated
with liquid phase.
19
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
  • Acid wash (AW) removes metallic impurities
  • Acid wash and dimethyl dichlorosilane-treated
    (AW-DMCS) remove silanol groups

20
Examples of GC support materials
21
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
22
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

23
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

24
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
25
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

26
GC on polar liquid phase
230 C
Hydrocarbons
4 C/min
50 C
Essential oil (Cymbopogon nardus)
Column HP-20M (Carbowax 20M)
27
Comparison of Manufacturers Phases
28
Factors in selecting stationary phase
  • Nature of analyte
  • Stationary phase type
  • Column internal diameter
  • Film thickness
  • Column length

29
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
30
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
31
Column conditioning
  • Condition at
  • 20 oC higher than analysis temp
  • 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

32
GC Applications
  • Petrochemical
  • Environmental
  • Forensic
  • Pharmaceutical
  • Oleochemical
  • Others

33
GC Profile of Diesel
  • ..

34
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.
35
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).
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