1. ATTENUATED TOTAL
REFLECTANCE-FTIR
Sahana V
PGD
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2. Outlook
 Internal Reflection Spectroscopy
 Infrared beam reflects from a interface via total
internal reflectance.
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3. A little detail
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Incident waveReflected wave
Evanescent wave

4. Edge over Traditional methods
 Little or no sample preparation
 Very thin sampling path length
 Depth of penetration of the IR beam into
sample
 Sample analysis- faster (less than 1 minute for
thick samples)
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5. How it works
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6. Factors
 Wavelength of IR radiation – λ
 Refractive indexes of sample and IRE*- n(s), n(IRE)
 Angle of incidence of IR radiation- θ
 Depth of penetration(pathlength)- d
 Sample and IRE contact efficiency
*Internal reflection element
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7. Instrumentation
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8. Continued
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1 2
3 4

9. CRYSTAL MATERIALS
MATERIAL ATR
SPECTRA
RANGE
REFRACTI
VE INDEX
DEPTH OF
PENETRATI
ON
USES
Germanium 5,500-675 4 0.66 Good for most
samples. Strong
absorbing samples,
such as dark polymers
Silicone 8,900-
1,500 and
360-120
3.4 0.85 Resistant to basic
solutions
AMTIR 11,000-725 2.5 1.77 Very resistant to acidic
solutions
ZnSe 15,000-650 2.4 2.01 General use
Diamond 25,000-100 2.4 2.01 Good for most
samples. Extremely
caustic or harder
samples.
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10. Selecting a right crystal
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11. Disadvantages
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 The ATR crystal absorbs energy at lower
energy levels
 If the sample does not have good contact with
the crystal, the data will not be accurate
 Most ATR crystals have pH limitations

12. Applications
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Solid Analysis Liquid Analysis Powder Analysis
excellent technique for
measuring the
composition of solids
analyze non-aqueous
solutions
easier to run by ATR
than by IR transmission,
because little or no
preparation is required
ideal technique for
measuring dark colored
materials which often
absorb too much energy
to be measured by IR
transmission
Cleanup is easy and fast pure samples and
mixtures that are
available in powdered
from
films, fabrics, paper,
hard polymer sheets,
glass, rubber
lubricants, oils, paints,
glues, solvents, inks and
dyes,
Gels and pastes can
pharmaceuticals and
pigments

13. End Notes
 Versatile and non-destructive technique for
variety of materials- soft solid materials,
liquids, powders, gels, pastes, surface layers,
etc.
 Useful for surface characterization, opaque
samples
 Limitations: sensitivity is typically 3-4 orders
less than transmission
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14. References
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 http://www.azom.com/article.aspx?ArticleID=5
958
 Perkin-Elmer: Technical Note
 SpectraTech: Technical Note