Foundation GPC Training Course Theory

Nomenclature Gel Permeation ChromatographyGPC Size Exclusion ChromatographySEC Gel Filtration ChromatographyGFC

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., mm 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 Performance t R = retention time W ½ = peak width at 50% peak height W 5  = peak width at 4.4% peak height L = column length in meters Efficiency (½ height) N=5.54(t R /W) 2 L Plate count efficiency (5  ) N=25(t R /W 5  ) 2 L Symmetry =W 1 /W 2

Resolution in GPC  Resolution Rs =2(V 1 -V 2 ) (W 1 +W 2 )  Specific Resolution per Molecular Weight Decade Rsp =0.25  D  Elution Volumes of peaks 1 and 2 are V 1 and V 2  Peak Widths of peaks 1 and 2 are W 1 and W 2