Effect of Packing Particle Size on Plate Height

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Effect of Packing Particle Size on Plate Height
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Resolution between 2 adjacent peaks
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The General Elution Problem
Small k'
Large k'
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The General Elution Problem
1. Poor separation of compounds with
small capacity factors. 2. Excessive separation
time and poor detectability of compounds with
large capacity factors.
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Solutions to The General Elution Problem
Alter k' values during the separation 1. Tempera
ture Program (GC) 2. Gradient Elution
(LC) 3. Coupled Columns (change the stationary
phase) Temperature programming and gradient
elution require re-equilibration time after the
analysis of each sample.
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Temperature Programming Separation of Normal
Alkanes (C6 C12)
Ti 100oC Tf 200oC
Tc 130oC
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12
0
0
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Gradient Elution Substituted Benzenes
Organic
Water
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GAS CHROMATOGRAPHY
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GAS CHROMATOGRAPHY INSTRUMENTATION 1. Mobile
Phase 2. Sample Injector 3. Column (Stationary
Phase) 4. Detector
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GC MOBILE PHASES 1. He 2. H2 3. N2 4. CO2
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GC On-Column Injector
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GC Glass-lined Injector for a Packed Column
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GC Injector for a Capillary Column
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GC Split Injector for a Capillary Column
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GC Split-less Injector for a Capillary Column
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GC Stationary Phases
PDMS PolyDiMethylSiloxane Organic stationary
phases must have sufficient molecular weight to
achieve low volatility
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GC Stationary Phases
Increase Polarity by adding phenyl rings or CN
groups
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GC Stationary Phases
Or by de-shielding the oxygen and forming a
wax. (Carbowax)
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GC Stationary Phases
Decrease Polarity by replacing methyl groups with
longer chain alkanes.
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GC Stationary Phases Types
Non-Bonded Liquid phase is used to coat the
inside walls of the column to a thickness of
about 0.1 1.0 µm Bonded Silanol groups on
the column wall form a chemical bond with the
stationary phase
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GC Stationary Phases Types
Preparation of Bonded Phases
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GC Stationary Phases Types
Advantage of Bonded Phases 1. High
Reproducibility 2. Low Bleed 3. Fast
Equilibration 4. Temperature Stability 5. Easy
to Back Flush 6. Long Life
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GC Stationary Phases Types
What about Packed GC Columns??
Open Tubular Column
Packed Column
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GC Stationary Phases Types
FSOT Fused Silica Open Tubular WCOT Wall
Coated Open Tubular SCOT Support Coated Open
Tubular WCOT and SCOT are less flexible and more
fragile (made of glass) FSOT with bonded phase
is most common N 400,000 H 0.1 mm L 50 m
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GC Stationary Phases Types
Packed Column H A B/u Cu C? dp2
(particle diameter)2 Open Tubular H B/u
Cu C ? dc2 (column internal diameter)2
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Open Tubular
Packed
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Open Tubular Columns
tr ? dc ?/(Po Dm)1/2 where ? mobile phase
viscosity Po column outlet pressure Dm Diffusion
coefficient of analyte in gas dc Internal column
diameter Dm ? MW-1/2
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Open Tubular Columns
So tr ? ? MW1/21/2 Gas ?
MW1/2 Ar 1138 CO2 995 N2 741 He 440 H2
90
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Open Tubular Columns with Different Gases