Gel permeation chromatography (GPC) is used to determine the molecular weight distribution of polymers. GPC separates polymer molecules of different sizes as they pass through columns containing porous gel beads. Smaller molecules penetrate deeper into the pores than larger molecules, allowing separation by "effective size in solution." Detectors then provide data used to calculate number average molecular weight, weight average molecular weight, and molecular weight distribution. GPC is a convenient and common technique for characterizing polymer molecular weights.

1. THE INSTITUE OF SCIENCE ,MUMBAI .
Topic: Molecular weight
determination by GPC/SEC.
Paper:1
semister-3
-sana shaikh.
M.sc part –two.
sem-three.

2. Molecular weight of polymers.
• Determines many physical properties.
( e.g. :temperatures for transitions ).
• Determines many mechanical properties.
(e.g.: stiffness, strength, toughness ).
• Molecular weight .
• transition temp& mechanical properties .

3. The molecular weight of polymer is not one unique value ,rather a
given polymer will have distribution of molecular weights.
Mn= number average molecular weight.
Mw =weight average molecular weight.
Mv=viscosity molecular weight.
Mz= average molecular weight.

4. Methods for determination of molecular weight of polymers.
• A=absolute, R=relative, E=equivalent

5. “absolute” – the measurement is directly related to the molecular weight
without assumptions about chemical and/or physical properties of the
polymer.
“equivalent” – the chemical structure of the polymer must be known to
obtain molecular weight.
“relative” – the quantity measured depends on the physical structure of
the tested polymer and so a calibration curve relating measurement and
molecular weight values must be known .

6. Gel permeation chromatography (GPC)
• Gel permeation chromatography (GPC) is one of the most
powerful and versatile analytical techniques available for
understanding and predicting polymer performance.
• It is the most convenient technique for characterizing the
complete molecular weight distribution of a polymer.
• GPC can determine several important parameters. These
include number average molecular weight, weight average
molecular weight and the most fundamental characteristic of
a polymer its molecular weight distribution.

7. How GPC works.
• GPC separates molecules in solution by their "effective
size in solution.“
• To prepare a sample for GPC analysis the resin is first
dissolved in an appropriate solvent.
• Inside the gel permeation chromatograph, the
dissolved resin is injected into a continually flowing
stream of solvent (mobile phase). The mobile phase
flows through millions of highly porous, rigid particles
(stationary phase) tightly packed together in a column.
• The pore sizes of these particles are controlled and
available in a range of sizes.

8. GPC Systems.
• In designing instrumentation for GPC, a variety of
requirements must be satisfied. Injectors are needed to
introduce the polymer solution into the flowing
system. Pumps deliver the sample and solvent through
the columns and system.
• Detectors monitor and record the separation. Data
acquisition accessories control the test automatically,
record the results, and calculate the molecular weight
averages.
• The gel permeation chromatograph contains a number
of different components that work together to provide
optimum system performance with minimum effort.

9. Phases.
• Stationary phase: Composed of semi-permeable, porous polymer gel
beads with well defined range of pore sizes .
• Properties of gel beads:
• Chemically inert
• Mechanically stable
• Has ideal and homogeneous porous structure (wide pore size give low
resolution).
• Uniform particle and pore size.
• The pore size of the gel must be carefully controlled.
• Mobile Phase: Composed of a liquid used to dissolve the biomolecules to
make the mobile phase permitting high detection response and wet the
packing surface

10. Separation depending on size.

11. First GPC demonstrations performed
by Waters

12. THEORY OF SEPARATION.
A column is made up of swollen gel particles and the solvent used to swell the gel
in a suitable tubular container.
Vt =V0+ Vi + Vm
Vt =the total volume of the column (which can be measured)
Vi =the volume of the liquid inside the matrix
Vm =the volume of the gel matrix.

13. MWD (CURVE).
• The width of the individual peaks reflects the distribution
of the size of molecules for a given resin and its
components.
• The broader the MWD, the broader the peaks become
and vice versa.
• You can see then how easily the MWD profiles of two resins
can be compared. If the MWD profile of an incoming resin
doesn't match that of the control resin (i.e. one that is
known to process well) closely enough, the incoming resin
can be modified or process conditions can be changed to
make sure the resin processes properly.

15. Schematic of a basic gel permeation
chromatograph.

16. GPC/SEC.

17. Components.
• 1. Pump
• Pumps the polymer in solution through the system.
• Different polymers produce solutions of different viscosities. To compare
data from one analysis to the next, the pump must deliver the same flow
rates independent of viscosity differences. In addition, some detectors
are very sensitive to the solvent flow rate precision. Such constant flow
must be a critical feature of the instrument.
• 2. Injector
• Introduces the polymer solution into the mobile phase.
• The injector must be capable of small volume injections (for molecular
weight determinations) and large volume injections (if fraction collecting
is desirable). The injector should not disturb the continuous mobile phase
flow. It should also be capable of automatic multiple sample injection
when the sample volume is large.

18. Pumps.
• Syringe or reciprocating pumps with highly
constant flow rate are commonly used.

19. Components.
• 3. Column Set
• Efficiently separates sample components
from one another.
• High efficiency columns give maximum
separating capability and rapid analyses.
Every column must provide reproducible
information over extended periods for both
analytical and fraction collecting purposes.

20. Columns.
• Commercially available
columns include.
• Analytical columns-7 to
8 mm in diameters.
• Preparative columns-22
to 25 mm
• Narrow bore columns-2
to 3 mm

21. Components.
• 4. Detector
• Monitors the separation and responds to components as they
elute from the column.
• In addition, the detectors must be sensitive. Since all compounds
refract light, the differential refractometer (RI) is referred to as a
"universal" detector. As a result it is the most widely used detector
to monitor molecular weight distribution. The refractive index of
polymers is constant above approximately 1000 MW. Therefore, the
detector response is directly proportional to concentration.
• Beside information about molecular weight averages and
distribution obtained with RI, the use of UV absorbance detectors
may provide information about composition, while on-line light
scattering detectors and viscometers provide information about
polymer structure.

22. Detectors.
refractometer Light scattering detector

23. Data processing equipments.
• Automatic data processing equipment
• Automatically calculates, records, and report
numerical values for Mz, Mw, Mv, Mn, and
MWD.
• Data systems can also provide complete
control of GPC systems so that large numbers
of samples can be run unattended and raw
data can be automatically processed.

24. Advantages
• Well-defined separation time .
• Narrow band .
• Lower chances for analyte loss occur.
• Most convenient method .
• Samples can be thoroughly analyzed in an
hour or less.
• Quick and relatively easy estimation of
molecular weights

25. Disadvantages
• Limited number of peaks that can be resolved.
• Requires 10% difference in molecular weight
for reasonable resolution peaks.
• Filtrations must be performed before using
the instrument ,there are possibility of pre-
filtration removing higher molecular weight
sample before it can be loaded on the column.

26. Reference .
• Polymer analysis-Barbara Stuart.
• Textbook of polymer science-Fred
w.billmeyar,jr.
• Principles of polymer science ,second edition
–p bahadur .n v sastry.
• IMG SOURCE
:http://www.waters.com/waters/en_IN/Size-
exclusion-chromatography-%28SEC%29-Gel-
Permeation-Chromatography-%28GPC%29-
Guide/nav.htm?cid=10167568&locale=en_IN

27. Thank you .