foundation gpc training course theory

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 well-defined 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 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

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

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