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Transmission TechniquesTransmission TechniquesSolidsSolids

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Solid Transmission Analysis

Pressed PelletMullPressed FilmCast Film

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o

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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)