introduction to gas chromatography - young in · introduction to gas chromatography young in...

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Young In Scientific Co., Ltd.

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Introduction to Gas ChromatographyIntroduction to Gas Chromatography


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Objectives

• To know what is chromatography

• To understand the mechanism of compound separation

• To know the basic of gas chromatography system

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Chromatography Definition

Chromatography, The Science of Separation

A physical method of separating sample components from a mixture by selective adsorption or partitioning of the analyte between two phases:

a mobile phase & a stationary phase


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Chromatography Phases

• Mobile Phases:– Liquids (methanol, water…)

• Changing dielectric strength– Gases (helium, hydrogen…)

• Temperature

• Stationary Phases:– Solids (alumina, silica, carbon…)

• Adsorption chromatography– Liquids (siloxanes, polyethylene glycols…)

• Partition (distribution) chromatography

Seminar Focus: GLC (Gas-Liquid Chromatography)

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GC & HPLC Applicable Ranges

HPLCGC


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Classification of chromatographic methods

GSC GLC

Packed

WCOT SCOT PLOT

OpenTubuler

Gas Liquid

Column Chromatography

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GLC vs. GSC

Liquid Phase

Solid SupportVery porous with veryhigh surface area

Carrier Gas

Carrier Gas

Absorbent packingPorous with large surface area

Gas Solid Chromatography (Packed column)

Gas Liquid Chromatography (Packed column)


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WCOT vs. SCOT vs. PLOT

Carrier GasSolid Phase

Porous Layer Open Tubuler (PLOT)

Wall Coated Open Tubular (WCOT)

Liquid PhaseCarrier Gas

Support Coated Open Tubular (SCOT)

Liquid PhaseCarrier Gas

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Types of GC Capillary Columns

• WCOT (wall coated open tubular)– Partition chromatography– Typical phases: Siloxanes and Carbowaxes – 0.10 through 0.53mm internal diameters

• PLOT (porous layer open tubular)– Adsorption chromatography– Permanent gas and light hydrocarbon analysis– Adsorbents: molecular sieve, porous polymers, alumina...


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The history of Chromatography

• Term first applied by M.S.Tswett in 1903– “Inventor of chromatography”– Separation of plant pigments on adsorbents

• L.S. Palmer in 1922– American who revived technique– Separation of natural products

• Martin and Synge in 1941– Used silica gel packing– Introduced partition chromatography– Awarded the Nobel Prize in chemistry 1952 with Plate

theory for chromatography

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Separation process

Garrier Gas


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The Principal of Separation

Intermolecular interactionsbetween stationary phase and sample compound

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Intermolecular Interactions on GC column

Hydrogen Bonding

Dipole-Dipole Interaction

Dispersive Interaction

ReactionsReactionsIntermolecular InteractionIntermolecular Interaction


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Basic Gas Chromatography

• The walls of a small diameter piece of tubing (column) of lengths from 1 to over 50 meters are coated with a high temperature liquid (usually a silicone oil).

• A low flow of pure carrier gas (Nitrogen, Helium, or Hydrogen) is passed through the column while the column is maintained at a constant temperature. One end of the column has a high temperature rubber cover that can be penetrated by a small syringe needle. The other end is connected to a detector (e.g. flame ionization detector).

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Gas Chromatograph System

Carrier Gas Purifier

Display

Pneumatic Controls

Inlet

Oven

Column

Detector

Data System


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Characteristics for Gas Chromatography

• Not easy to recover the sample.• Hard to analyze the heat labile sample.• Hard to introduce the reproducible amount of sample• Limited mobile phase (gas)

• Easy to handle• Low maintenance cost• Fast Analysis• High Resolution• Easy to hyphen with MS and other detecting tool• Requires small samples, typically µL• Highly accurate quantitative analysis, typical RSDs of 1-5%

LimitationsLimitationsAdvantagesAdvantages

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Compounds Amenable to Gas Chromatography

• Moderately thermally stable• Vapor pressure in column (boiling point) allows for partitioning

– Routinely used below F.W. ~ 1000 amu– Permanent gases through F.W. ~ 2000 amu for certain

compound classes• Unreactive/non-absorptive to chromatographic system

1 amu (atomic mass unit) = 1.660538 × 10-27 kilograms


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• Inert gases like, He, H2, N2, Ar

• Prefer low diffusible gases.

• Purity : referred to as five 9s or 99999 grade

– No air, water, hydrocarbons and etc.

• Adequate to GC detector

Carrier Gas (Mobile phase for GC)

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Carrier Gas for each GC detector

Provide highest sensitivity N2

Provide highest sensitivityN2ECD

Most wide dynamic rangeAr/CH4

GoodN2FID

Not bad H2,He

BestHeNPD

GoodN2FPD

For the analysis of hydrogenN2

Provide highest sensitivityH2

Popular GC

Detectors

GoodHeTCD

DescriptionCarrier GasDetector


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A : Moisture trapB : Hydrocarbon trapC : Indicating Oxygen trap

Gas purifying system for GC

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Separation - The Ultimate Goal

• The sample transfer or injection technique• Column choice

– Partitioning – Selectivity– Resolution

• The detection method– FID, ECD, GC/MS…

Many Factors Affect Separation


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Separation Step 1 — Sample Transfer

• Injection — how the sample is transferred to the column – As a liquid via syringe– Non-liquid techniques

• Purge & trap• Headspace• Gas sample loop

NOTE: It is critical to get the sample into the column in a focused band…

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due to carrier gas flow profiles and increased diffusion when in the gas phase

...because analytes Band Broaden in time and space

Final BandwidthInitial

30 m0 meters

• Bandwidth (peak width) increases as an analyte travels along the column


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Band Broadening

Eddy diffusion

Molecular diffusion

Therefore, producing a narrow initial bandwidth (focusing)is critical to separation!

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How to get a focused initial band:

• Solvent Focusing– Set oven temp. lower than boiling point of all analytes and

solvent (approximately 20°C lower)

• Analyte Focusing– If solvent boiling point is much lower than boiling point of first-

eluting analyte, set oven temp. lower than boiling point of thatanalyte

Separation Step 1 — Sample Transfer


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Partitioning

• Oven temp. increased until effective vapor pressures are reached and compounds leave the column head

• Compounds flow with the carrier gas until they partition into the stationary phase

• Partitioning is a function of:– Stationary phase type– Column dimensions– Oven temperature– Carrier gas type and linear velocity

Separation Step 2 — Column choice

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e.g. DB-1 column 100% Dimethyl Polysiloxane

Separation Step 3 – Column choice

OOO O O

Si Si Si Si

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

Selectivity


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ResolutionNot Efficient, but Selective

Efficient and SelectiveEfficient, but not Selective

Not Efficient, not Selective

Separation Step 3 – Column choice

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Flame ionization detector (FID)Materials that ionize in an air/H2 flame

Nitrogen phosphorus detector (NPD)Organic compounds containing nitrogen & phosphorus

Electron capture detector (ECD)Poly-halogenated compounds, organometallics, conjugated carbonyls etc.

Flame photometric detector (FPD)Sulfur (or P) containing compounds.

Etc.

Separation Step 4 — Detection


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Real Example

Run Conditions:30m, 0.32mm ID, 0.50 µm DB-1

Component list:1. 2,4,5,6-tetrachloro-m-xylene2. alpha-BHC3. gamma-BHC4. beta-BHC5. delta-BHC6. heptachlor7. aldrin8. heptachlor epoxide9. gamma-chlordane10. alpha-chlordane11. 4,4'-DDE

12. endosulfan I13. dieldrin14. endrin15. 4,4'-DDD16. endosulfan II17. 4,4'-DDT18. endrin aldehyde19. methoxychlor20. endosulfan sulfate21. endrin ketone22. decachlorobiphenyl

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Summary

• History• Fundamentals• Factors for achieving a GC separation• Terms:

– Selectivity, Partitioning, resolution• Focusing and separation

introduction to gas chromatography - young in · introduction to gas chromatography young in...

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