Foundation GPC Training Course
Theory
Nomenclature
Gel Permeation Chromatography
GPC
Size Exclusion Chromatography
SEC
Gel Filtration Chromatography
GFC
Types of Liquid Chromatography
Interactive adsorption, partition, ion exchange, etc
Non-interactive GPC, SEC, GFC
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
Size Exclusion Mechanism
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
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
Synthesis of Porous Particles
 High
cross-link content
gives a rigid, low swelling
product with a welldefined pore structure
SEM Images of Porous Particle of PLgel
10µm Media
Elution Profile of Different Molecular Sizes
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
PLgel Individual Pore Size Column
Calibration Curves
PLgel MIXED Column Calibration Curves
Plate Counts
 A measure of the efficiency of
a chromatographic system is the
plate count
 Column
is divided into
number of theoretical plates
a
 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
Determination of Column Performance
tR = retention time
W½ = peak width at 50% peak
height
W5s = 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 (5s)
N=25(tR/W5s)2
L
Symmetry =W1/W2
Resolution in GPC


Resolution Rs

2(V1-V2)
(W1+W2)
Specific Resolution per Molecular
Weight Decade
Rsp

=
= 0.25
sD
Elution Volumes of peaks 1 and 2
are V1 and V2
Peak Widths of peaks 1 and 2 are
W1 and W2