ADVANCED BIO-FRIENDLY POLYMERS
Gel permeation chromatography – a tool
for determination of molar mass of
polymers
Igor Lacík
Molecular weight: characterization techniques
Mn
 techniques related to colligative properties (dependence on the number of molecules)
 membrane osmometry (> 25 000 g/mol)
 vapor pressure osmometry (< 25 000 g/mol)
 mass spectrometry
 electrospray ionization mass spectrometry (ESI-MS)
 matrix-assisted laser desorption/ionization (MALDI)
 size exclusion chromatography
Mw
 static laser light scattering
 analytical ultracentrifuge
 size exclusion chromatography
Mw
wi
Mz
Mn
 static laser light scattering
 analytical ultracentrifuge
 size exclusion chromatography
Mz
Mi
M
 viscometry
 size exclusion chromatography
Molecular weight: characterization techniques
Mn
 techniques related to colligative properties (dependence on the number of molecules)
 membrane osmometry (> 25 000 g/mol)
 vapor pressure osmometry (< 25 000 g/mol)
 mass spectrometry
 electrospray ionization mass spectrometry (ESI-MS)
 matrix-assisted laser desorption/ionization (MALDI)
 size exclusion chromatography
Mw
 static laser light scattering
 analytical ultracentrifuge
 size exclusion chromatography
Mw
wi
Mz
Mn
 static laser light scattering
 analytical ultracentrifuge
 size exclusion chromatography
Mz
Mi
M
 viscometry
 size exclusion chromatography
Size-exclusion chromatography – principle
1. Column separation technique
2. Based on enthalpy-free partitioning of analyzed solutes, most often the polymer
chains, of different molecular weight / length (size) between mobile and stationary
phases
Separation mechanism is based on the size
Stationary phase
• pore size
• pore size distribution
• particle size
Mobile phase 
• flow rate in ml/min providing “elution volume, Ve” or elution time, te ”
Separation mechanism is based on the size
Time 3
Time 2
Time 1
Time 1 < Time 2 < Time 3
Ve,1 < Ve,2 < Ve,3
Size-exclusion chromatography – principle
1. Column separation technique
2. Based on enthalpy-free partitioning of analyzed solutes, most often the polymer
chains, of different molecular weight / length (size) between mobile and stationary
phases
Ve  V0  Kd (Vt  V0 )
Kd - partition coefficient 0  Kd  1
solute exluded
solute permeated
Ve - elution volume for given size
Velution
V0 - interstitial volume (between particles
of column packing)
Vt - total available volume of column
(interstitial and pore volumes)
Size-exclusion chromatography – setup
Injection of polymer
of unknown molecular
weight characteristics
Pump
eluent
Commercial columns of defined
characteristics for column
packing:
diameter, exclusion
limit, pore-size
distribution
Detector
signal = f(elution volume)
calibration curve
with standards:
elution volume = f(MW)
molecular weight
characteristics
(MWD, Mw, Mn) of polymer
molecular weight distribution
calibration curve
signal
exclusion
log M
sign al
detector
separation
permeation
elution volume
elution volume
log M
GPC signal  w(logM )  ln(10) M f w ( M )  ln(10) M 2 f n ( M )
Size-exclusion chromatography – hardware
DEGASSER
MALLS
MAREK
PUMP INJECTOR COLUMNS
SOFTWARE
RI
Rheodyne inj. or Waters Autosampler
Degasser
Pump
Waters 515
Columns
MALLS
SLD7000
DRI Detector
Waters 2410
WinGPC®7.4
Software
Size-exclusion chromatography – calibration
SEC is an indirect method
 needs RELATION of elution volume (volume slice) to molecular
weight = calibration
• several types of calibration
1. narrow distributed standards of the same polymer
 1.1
Mw / Mn
2. universal
calibration
[]1 M1 = []2 M2 ~ size of coil ~ Velution (Benoit et al, 1966)
note: a) Mark-Houwink equations is related to MW range
b) careful in low MW range where a ~ 0.5 J.Polym.Sci. 6, 1759 (1968)
3. absolute molecular weight detectors
(LS, viscosity)
4. effective calibration (no match between standards and analyzed
polymer)
decrease in accuracy
Size-exclusion chromatography – hints/experience
Remember  suppress interactions to avoid non-SEC phenomena
(1) polymer - polymer (aggregation) – earlier elution, artificially increased
molecular weight
(2) polymer - column packing (adsorption) - delayed elution, artificially
decreased molecular weight
(3) eluent-column packing (repulsion) – earlier elution, artificially increased
molecular weight
(4) polymer - eluent (aggregation) - earlier elution, artificially increased
molecular weight
(5) etc.
Size-exclusion chromatography – hints/experience
Remember  suppress interactions to avoid non-SEC phenomena
water-soluble polymers (polyelectrolytes)
Problem
•H-bonding
•hydrophobic interactions
•polyelectrolyte effect
•adsorption (ion inclusion)
•repulsion (ion exclusion)
•calibration
•concentration effect
•resolution (eluent viscosity)
Cure
Eluent composition
&
column selection
PSS
TosoH Biosep
Polym. Laboratories
Waters
Direct calibration with
standards of well-defined Mp
Optimized solute concentration
Temperature of analysis
Suprema
HEMA
GRAM (DMAc)
TSK PWXL
Ultrahydrogel
Size-exclusion chromatography – hints/experience
Remember  suppress interactions to avoid non-SEC phenomena
water-soluble polymers (polyelectrolytes like poly (acrylic acid))

eluent: 0.1M LiNO 3 , 0.04 M phosphate bufer, pH 8.0, 0.01M NaN

columns: Suprema 100, 1000, 3000, 10 00

flow rate 0.6 -1.0 ml/min (ethylene glycol

temperature 60-80ºC

calibration p(NaA) standards 1 250

sample: concentration 0.5 - 2 mg/ml, injection volume 200 mL

data acquisition and evaluation
0 Å (8 x 300 mm, 10
3
mm)
– internal standard)
– 1 100 00 0 g/mol (PSS, Mainz, Germany)
WinGPC 7 (PSS, Mainz, Germany)
system peaks
- salt excluded
from PE region
or
0.1M Na2HPO4 (pH 9)
or other compositions
EG
sample
Size-exclusion chromatography – hints/experience
Remember  suppress interactions to avoid non-SEC phenomena
Calibration curve (polyacrylic acid)
Guide-lines:
• no upward curvature at high M.w,
i.e. no adsorption of PAA to column packing
(solute-gel interactions) pronounced at  M.w.
• variation of ionic strength - test to estimate the
interactions
 ionic strength too low: elution volumes
increase due to electrostatic interactions
 ionic strength too high: elution volumes
increase due to hydrophobic interactions
 remove charged monomer by dialysis: as it
adds to the ionic strength of eluent
 a suitable ionic strength is in case of the
lowest elution volumes
Size-exclusion chromatography – hints/experience
Remember  suppress interactions to avoid non-SEC phenomena
Concentration effect (polyacrylic acid)
22.0
5.0
0.9
0.8
3.0
0.6
0.5
0.4
4. 02
1.0
0.2
0.7
s c ie n t if ic
0.1
0.3
W in G P C
V
0.3
PSS
rel . W(l og M)
0.7
0.0
10 3
10 4
10 5
10 6 g/mol
8E+5
6E+5
21.0
4E+5
2E+5
20.0
0
1
2
3
4
5
M ol m ass
 decrease in hydrodynamic volume of polymer coil at higher polymer concentration
leads to the artificially lower M.w.
 lowering the sample concentration until the constant molar mass is reached yet detector
sensitivity is sufficient
6
Molar mass at peak [g/mol]
1.0
Elution volume at peak [ml]
PAA concentration
in mg/ml
1.1
Size-exclusion chromatography – hints/experience
Accuracy of the flow rate (polyacrylic acid)
! EXTREME SENSITIVITY TO VARIATION IN THE FLOW RATE!
Elution volume of
Difference
Mp
Difference in Mp
internal standard
[%]
[g/mol]
[%]
36,525
0
57 700
0
36,342
- 0,5
55 000
- 4,7
36,160
- 1,0
50 700
-12,1
35,794
- 2,0
42 600
-26,2
36,707
+ 0,5
64 300
11,4
36,890
+ 1,0
69 300
20,1
37,256
+ 2,0
80 000
38,6
[ml]
EG
sample
adjusted
sample
V
V
analysis
sample
n
 Vintcalibratio
. s tan dard

 Vintanalysis
 . s tan dard




 it is essential flow rate is controlled by the flowmarker (ethylene glycol) which
also controls the pore volume and any changes on columns
Size-exclusion chromatography – hints/experience
Effect of temperature of analysis (polyacrylic acid)
2.0
Viscosity [mPa.s]
Water
room T
1.5
Toluene
THF
1.0
0.5
0.0
0
20
40
60
80
Temperature [ C]
 the partitioning of the solute between mobile and stationary phases depends on viscosity of
mobile phase: improved partitioning  improved resolution
 viscosity of aqueous mobile phase can be adjusted to that of the organic one by the
temperature of analysis
Size-exclusion chromatography – hints/experience
Final hints with special emphasis to the aqueous-phase SEC
•
fast advancing in the last years with strong achievements
(columns and new experience)
•
there exist more and more examples of very precise analysis with
high resolution (a strong improvement in aqueous-phase SEC)
•
patience in thorough testing after thinking of all the possibilities
which may hamper the experiment
•
column history may play a role (more in aqueous-phase SEC than
in aqueous-phase SEC)
Size-exclusion chromatography – final slide
This is also the common SEC analysis 