atr

1. Submitted by,
Renatt. c. Francis
1st year M.Pharm,
Pharmacy Practice
Attenuated total
Reflectance
(ATR)

2. •Attenuated total reflectance (ATR) is a
sampling technique used in conjunction with
infrared spectroscopy which enables samples to
be examined directly in the solid or liquid state
without further preparation
What is ATR

3. WHY ATR?
ATR generally allows
little or no sample
preparation, which
greatly speeds sample
analysis.
It allows very thin
sampling pathlength
and depth of
penetration of the IR
beam into the sample. 3

4. Evanescent Waves
•The infrared radiation interacts with the sample
through a series of standing waves, called
evanescent waves
•An evanescent wave is a penetrating electromagnetic
field whose intensity quickly decays as it moves
away from its source

5. Principle of ATR
• ATR spectroscopy utilizes the
phenomenon of total internal
reflection
• A beam of radiation entering a
crystal will undergo total internal
reflection when the angle of
incidence at the interface
between the sample and crystal
is greater than critical angle
• In this way, an evanescent wave
penetrates into the sample in
contact with the crystal,
producing a spectrum of the
sample

6. Conditions
 sample must direct contact with ATR
crystal
 The refractive index of the crystal must
be greater than that of sample

7. How it works???
7

8. • The depth of penetration in ATR spectroscopy is a function of the wavelength,
λ, the refractive index of the crystal, n2, & the angle of incident radiation , Ө.
• The depth of penetration , dp, for a non-absorbing medium is given by the
following:
where n1is the refractive index of the sample.

9. Crystal Composition
• Crystal used in ATR cells are made from materials that have low
solubility in water & a very high refractive index.
Crystals are typically made of:
• Zinc Selenide (ZnSe)
• Germanium (Ge)
• Diamond
• Zinc Sulfide (ZnS)
• Silicon (Si)

10. Advantage
•ATR sampling is fast and easy because little or no
sample preparation is required
•Other techniques, such as infrared transmission, often
require the sample to be heated, pressed or ground in
order to collect the spectrum

11. Disadvantages
• 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. References
• Organic spectroscopy by William kemp, page no92-94
• Instrumental Methods of Analysis, Willard, Merritt, Dean and Settle,
seventh edition, 311-315
• Analytical Chemistry Handbook, John A. Dean, 6.16-6.20
• Instrumental Methods of Analysis, Dr. Supriya S. Mahajan, 63-70

13. THANK YOU…