Foundation GPC Training Course Theory
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Transcript of Foundation GPC Training Course Theory
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Foundation GPC Training Course
Theory
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Nomenclature
Gel Permeation Chromatography GPC
Size Exclusion Chromatography SEC
Gel Filtration Chromatography GFC
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Types of Liquid Chromatography
Interactive adsorption, partition, ion exchange, etc
Non-interactive GPC, SEC, GFC
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Why do GPC ?
GPC is the only technique for characterising polymer molecular weight distribution
As Mw/Mn decreases the strength and toughness of the polymer increases
However as Mw/Mn decreases the polymer becomes more difficult to process
GPC provides key information to predict the processability and material properties of a polymer
MWD determined by GPC
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Size Exclusion Mechanism
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GPC Separation Mechanism
Polymer is prepared as a dilute solution in the eluent and injected into the system
The GPC column is packed with porous beads of controlled porosity and particle size
Large molecules are not able to permeate all of the pores and have a shorter residence time in the column
Small molecules permeate deep into the porous matrix and have a long residence time in the column
Polymer molecules are separated according to molecular size, eluting largest first, smallest last
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GPC Column Technology
Columns are packed with porous particles, controlled pore size and particle size
Columns are produced by slurry packing technique, packed at pressures in excess of 2000psi
Column dimensions typically 7-8mm i.d., 250-600mm in length
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Synthesis of Porous Particles
High cross-link content gives a rigid, low swelling product with a well-defined pore structure
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SEM Images of Porous Particle of PLgel 10µm Media
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Elution Profile of Different Molecular Sizes
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Elution Profile – Nomenclature
Exclusion volume (Vo) - Upper MW limit
(also known as void volume)
Total permeation volume (Vt) – Lower MW limit
Pore volume (Vp) – Working resolving range of MW
Vp = Vt - Vo
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PLgel Individual Pore Size Column Calibration Curves
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PLgel MIXED Column Calibration Curves
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Plate Counts
A measure of the efficiency of a chromatographic system is the plate count
Column is divided into a number of theoretical plates
Plates are defined as the smallest cross-sectional slice in which the mobile and stationary phases are in equilibrium
The smaller the width (known as height) of the plate, the quicker the system comes to equilibrium and the greater the efficiency
Plate counts controlled by the Van Deemter relationship
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Determination of Column PerformancetR = retention time
W½ = peak width at 50% peak height
W5 = peak width at 4.4% peak height
L = column length in meters
Efficiency (½ height)
N=5.54(tR/W)2
L
Plate count efficiency (5)
N=25(tR/W5)2
L
Symmetry =W1/W2
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Resolution in GPC
Resolution Rs =2(V1-V2)
(W1+W2)
Specific Resolution per Molecular Weight Decade
Rsp = 0.25 D
Elution Volumes of peaks 1 and 2 are V1 and V2
Peak Widths of peaks 1 and 2 are W1 and W2