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Transcript of This presentation exemplifies the latest Power Point dogma. 1 A full sentence at the top tells the...
This presentation exemplifies the latest Power Point dogma.
1
A full sentence at the top tells the main point.
Vertically aligned lists are avoided in favor of diagonal arrangement to create visual tension.
A page number helps reader ask questions.
Tasteful use of animation helps.
Occasionally, put in something strange or fun to keep professors and other tired listeners awake.
dogma, n. A settled or established opinion, belief, or principle
“You cannot measure absolute molecular weights”Dow manager, 1983Wrong!
Correct, even in 1983: you NEED NOT always measure ABSOLUTE molecular weights…but you could have.
Correct in 2005: it is almost always essential to measure absolute M s.
2
Here is the easiest equation in this talk.
SEC = GPC = GFCSize Exclusion Chromatography
Gel Permeation ChromatographyGel Filtration Chromatography
4
A riddle: After a hurricane, many trees fall over
and bend into a river. Also, a cow and a dog fall into that flooded river. Which one reaches the ocean first, cow or dog?
Moo!
Woof!
5
In GPC, as when throwing a cat through a tree, the big things come out first..
•Solvent flow carries molecules from left to right; big ones come out first while small ones get caught in the pores.
•It is thought that particle volume controls the order of elution.
•But what about shape?
6
Simple SEC is only simple when you don’t have to do it
yourself.
degas
pump
injector
DRIVe
log 10
M
c
c
log 10
M
c
log10M7
In simple GPC, you first make a map (calibrate),
then follow it.
Ve
log M
Vo
Ve
logM
A
DRI
VeA
DRIA
MA
8
Are you straight?GPC Calibration
log(Mw ) = 0.0009Ve3 - 0.0534Ve
2 + 0.6303Ve + 6.8161
R2 = 0.9996
0
20
40
60
80
100
120
14 16 18 20 22 24 26 28
Ve [mL]
Det
ecto
r R
espo
nse
0
1
2
3
4
5
6
7
8
log(
Mw)
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OK, but how did you get the M values for the standards?
• OsmometryScattering
MALDIAnalytical ultracentrifugation
End group analysisGoal in this class: make it seem
reasonable that it IS possible to measure M values.
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Osmometry is Real Science because it is tied closely to thermodynamics.
Semipermeable membrane: stops polymers, passes solvent.
h V = n R T
n = g/M
c = g/V
= c R T ...)1
( 2 cAM
12
Light scattering operates on thermodynamics; think of it as an osmometer without the membrane.
100,000
x
c
...)21
( 2,
1
cAM
cRTc
IpT
s
q
2
)2/sin(π4 o
nq
Teaching Light Scattering to Exemplify and Reinforce Basic Principles, D. S. Poche', P. S. Russo, B. Fong, E. Temyanko and H. Ricks, J. Chem. Ed., 1999, 76 (November), 1534-1538.
13
LS adds optical effects Size.
q = 0 in phase Is maximum
q > 0 out of phase, Is goes down 3
122g
s
RqI
14
This waterfall plot shows many “slices” of a chroma-togram: 13 angles were recorded ~8 times per second as the sample flowed by the MALS detector.
3D Plot - PBLG
4 5
6 7
8 9
10 11
12 13
14 15
16 Scatterin
g angle
Ve
Scattered intensity
16
The scattering “envelope” for a single slice shows how Is decreases with angle.
0.0 0.2 0.4 0.6 0.8 1.00
20000
40000
60000
80000
100000
120000
140000
c = 0.044 mg/mLM = 130000 g/mol
R/K
c
sin2( /2)
InterceptMolecular weight
SlopeSize
17
Intrinsic viscosity is a secondary molecular weight method so good it’s
almost like the real thing.Mark-Houwink-
Sakurada relationship between the intrinsic viscosity and the molecular weight.
aKM][ K and a are constants for a given polymer, not strongly dependent on solvent or temperature, as long as we’re talking about a “good solvent”.
These words have special meaning in polymer science.
aKM /1)/]([
19
Grubisic, Rempp & Benoit, JPS Pt. B, 5, 753
(1967)
One of of the most importantpapers in polymer science.Imagine the work involved!6 pages long w/ 2 figures.Selected for JPS 50th Anniv. Issue.
Universal Calibration lets you get the molecular weight of one kind of polymer knowing only the Mark-Houwink-Sakurada values of a standard (look it up) and your unknown (uh-oh).
20
Universal Calibration says that whatever comes out at a particular volume has the same product , []M.
[] = KM a
[]AMA = []SMS= f
(Ve)
11 SA aSS
aAA MKMK
Mark-Houwink Relation
Universal Calibration A = analyte; S = standard
Combine to get these two equations, useful only if universal calibration works!1
11
AS
S
a
A
aS
A K
MKM
21
Here is a small subset of GPC spare parts.
To say nothing of unions, adapters, ferrules, tubing (low pressure and high pressure), filters and their internal parts, frits, degassers, injector spare parts, solvent inlet manifold parts, columns, pre-columns, pressure transducers, sapphire plunger, and on it goes…
24
Other SEC Deficiencies• 0.05 M salt at 10 am, 0.1 M salt at 2 pm?• 45oC at 8 am and 50oC at noon? • Non-size exclusion mechanisms: binding.• Big, bulky and slow (typically 30
minutes/sample).• Temperature/harsh solvents no fun.• You learn nothing by calibrating.• Columns are expensive, easily damaged.
25
Must we separate ‘em to size ‘em?Your local constabulary probably doesn’t think so.
Atlanta, GAI-85N at Shallowford Rd.Sat. 1/27/01 4 pm
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Matrix Fluorescence Photobleaching Recovery* is an LSU-invented method designed to compete with GPC for certain systems (aqueous commodity polymers).
Indicates targeted M.
1000 10000 100000 10000000.0
0.2
0.4
0.6
0.8
1.0
Pullulan, 8% HPC Solution, M=12,200 and 48,000
CONTIN Exponential Exponential
FA
rbitr
ary
Un
its
M*G. J. Doucet, D. Dorman, R. Cueto, D. Neau, P. S. Russo, D. DeKee, J. Pople Macromolecules 2006, 39(26), 9446 – 9455.
27
Ultimate Goal: A Black Box for Ultimate Goal: A Black Box for MWDMWD
Matrix FPREasily Maintained
AccuratePrecise
Simple ConceptExpedient
Easy System SwitchBasic Info Obtained
MiniaturizableDetect Large MassesLabeling Required
GPCAccurate
Simple ConceptMiniaturizable
No Labeling RequiredBroad Distributions
PumpsParts
Press for MWD
DLSForm Factor
Index MatchingLong Acquisition for
Multiangle ExperimentsPrecise
Accurate
DOSYEasy System Switch
PreciseAccurate
Obtain Basic InfoLabeling Required
28
In other words, the search continues.
Two promising contenders are discussed next.
MALDI-TOF: most effective when the molecules are small, biological and not very polydisperse. Can be coupled to GPC!
FFF: like GPC only a flowing field replaces the stationary phase, stuff comes out backwards, and big stuff can be handled as well as small.
29
MALDI-TOF stands for Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry.
http://www.astbury.leeds.ac.uk/Facil/MStut/mstutorial.htm30
These data obtained at LSU: click the figure to analyze
these results.
0 2000 4000 6000 8000 10000 12000
0
100
200
300
400
File will download from the websiteCompute Mn,Mw,Mz MANUALLYCompute Mn,Mw,Mz in Excel or something elseYou can subtract the mass of silver from each peakWe hope Dr. Tracy McCarley will give a tour of the MALDI
a.i.C
ount
s
Mass
Guess what Mw/Mn is.
31
Patience is a virtue.
You 4010 students will get to practice with a MALDI dataset, but ….
that’s enough MALDI for now.
32
What about separating cows and elephants? Either will float around the trees. How do you separate them then?
Moo!
Eeee!
33
Field Flow Fractionation, that’s how!
In FFF, large nanoparticles are made to flow between plates; a field is applied to separate them by size.
34
The most commonly used field is flow itself: one or both plates are porous, and a cross-flow is arranged.
35
What happens because of the cross-flow?
Little nanoparticles come out first!At LSU, only one plate is porous. 1.Everyone calls it AF4 = Asymmetric Flow Field Flow Fractionation2.How to you get a crossflow then? 36
Potential Advantages of FFF
Handles a wider range of particles.May be easier for some aggressive
solvents.
37
30 35 4040
60
80
100
120
140
160
180
0.0
0.2
0.4
0.6
0.8
1.0
RMS radius vs Time
AF4 separation of algoflontm
LS 90o
rms
radi
us (
nm)
time (min)
rel
ativ
e in
tens
ity
AF4 can even separate large PTFElatex particles.
38