The world leader in serving science Transmission Techniques Solids.
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Transcript of The world leader in serving science Transmission Techniques Solids.
The world leader in serving science
Transmission TechniquesTransmission TechniquesSolidsSolids
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Solid Transmission Analysis
Pressed PelletMullPressed FilmCast Film
I
o
I
s
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Transmission Analysis
High sample throughputQualitative and quantitative
analysisRequires sample
preparationLow cost
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Pressed Pellet
Traditional Technique Great for powders and solids that
can be ground Uses a solid Matrix to dilute the
sample Pressing a consistent pellet
takes PRACTICEKBr Die Kit
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Technique
1) Grind the sample thoroughly to reduce scattering effects (Particle size < 10 m)
2) Mix sample with ground matrix material to obtain the proper ratio (Peak intensity ~ 10%T)
3)Combine sample and matrix in a ratio of ~1:100
4) Carefully transfer mixture to sample holder
5)Press
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Pressing Technique
1) Need to avoid trapping air in the sample matrix so use one of two methods:
-Press slowly releasing pressure often to allow compressed air to escape
-Run a vacuum line to the sample holder and evacuate before pressing
2) With hand presses, more pressure is better. With hydraulic press, use ~8000psi for 15 seconds
3)Good pellet should be clear
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Matrix Materials
Choose matrix based on properties and spectral range:• KBr (40,000-400cm-1)• CsI (40,000-200cm-1)• Polyethylene (650-50cm-1)• KCl (40000-500cm-1)• Diamond (4500-33cm-1) For temperature studies and “wet”
samples. Reusable Keep matrix dry if hydroscopic
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Types of Presses
Hydraulic Press• Reproducible• Easy to use• Excellent control• Expensive
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Types of Presses
Hand Press• Manual• Flexible• Inexpensive• User dependent
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Example
Universal Anvil
Collar
Upper AnvilHand Held Press
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Alignment
Use sample mount that allows maximum flexibility Position mount in sample compartment and find
interferogram signal Use laser position to determine approximate height of collar Loosen sample holder and reposition in x,y and angular
planes to maximize signal
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KBr Pellet Trouble Shooting
Inadequate pressure
Corrected spectrum
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Quantitative Analysis
Can generate acceptable results Need to measure matrix and sample quantity accurately Should try to apply same amount of pressure in creating pellet Reproducible particle size of sample is important
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Mull Suspension
Powders Waxy materials Eliminates physical changes
from other environments Easy and inexpensive
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Technique
Grind sample as much as possible Add a drop of the mulling oil and mix Continue to add drop wise and mix until mull has approximate
consistency of hand cream Transfer mull to window Use second window to seal system to avoid contamination. Universal sample holder provides excellent control
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Mulling Oils
Nujol
Fluorolube
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Subtracting Mulling Oil
Sample and Spectrum dependent Only works if mulling oil not totally
absorbing Searching the fingerprint region is a
convenient alternativeSample in Nujol
Nujol
Sample + Residual
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Split Mull
Caffeine in Nujol
Caffeine in Fluorolube
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Polishing Windows
Important to use clean, polished windows.
Reduces scattering and spectral drift
Easy to do
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Mull Troubleshooting
Insufficient sample grinding
Sample reground to smaller particle size
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Quantitative Analysis
Can generate good results but it is hard Need to use peak ratio or internal standard to compensate
for changes in pathlength Must stay away from frequencies where mulling oil could
interfere with calculations Reproducibility of particle size of sample is large factor in
error.
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Cast Film
Simple and effective technique
Great for rubbers, plastics, resins and viscous liquids
Dependent on finding a solvent
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Technique
Select suitable solvent and dissolve a small amount of sample Place drop of sample solution on compatible window or glass
slide(create a free standing film) Drying time varies with solvent and may need additional attention Be sure to evaporate all the solvent. Pockets may form and the
solvent bands will contaminate the sample spectrum
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Solvent Selection (Polarity Index)
Polar
Non Polar
Tetrafluoropropanol (9.3) Water (9.0)
Formamide (7.3) Methanol (6.6)
Dimethyl Sulfoxide (6.5) Acetic Acid or Acetonitrile or Methyl Formamide (6.2)
Pyridine (5.3))Ethylene Glycol or Acetone (5.4)
Nitrobenzene or Cyclohexanone or Methyl Ethyl Ketone (4.5) Chloroform (4.4)
Ethyl Acetate or 1-Propanol(4.3) Tetrahyrofuran (4.2)
Methylene Chloride (3.4) Ethyl Ether (2.9)
Phenyl Ether (2.8) Chlorobenzene (2.7)
P-Xylene (2.4) Toluene (2.3)
Isopropyl Ether (2.2)Carbon Disulfide (1.0)Cyclohexane (0)Hexane (0)
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Cast Film Trouble Shooting
Solvent
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Quantitative Analysis
Can generate good results Need to dry completely Inconsistent pathlength causes error Compensation of pathlength involves peak ratios or internal
standards.
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Pressed Film
Quick & Easy Minimal sample preparation Great for any samples that
melt Proper equipment gives
great quantitative results
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Techniques
Use small amount of sample in sample holder Choose a low heat setting Cover sample with flat, non-stick surface gradually heat to desired temperature and apply pressure until
sample softens and thins to desired thickness If fringing occurs, try matted surface
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Universal Film Maker
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SAMPLE
ALUMINIUM FOIL
TEMPERATURE CONTROLLER FOR HEATED PLATENS
HYDRAULIC PRESS
TOP HEATED PLATEN
BOTTOM HEATED PLATEN
Carver Press
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Temperature Effects
Want hot enough temperature to melt plastic -->create free standing film
Too hot will potentially burn sample (Volatilize) of thermally alter (spectral changes)
Too cool sample will not form thin enough film
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Interference Fringe
Constructive interference adds energyto the resultant wave
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Pressed Film Trouble Shooting
Interference Fringe
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Calculating Sample Thickness
92.2
92.4
92.6
92.8
93.0
93.2
93.4
%T
ran
smitt
an
ce
2400 2500 2600 2700
Wavenumbers (cm-1)
Thickness = Number of Maxima
2 (Refractive Index) (1 2
2767
2413
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Quantitative Analysis
Reproducible sample thickness major advantage Accurate control of pressure and heat necessary for
reproducibility Thickness of sample should be adjusted so that the
frequencies of interest absorb between .3-1 absorbance (50-10%T)