Attenuated total reflectance (ATR) method measures the infrared spectrum of the sample surface depth of 1 to 2 µm when sample and ATR prism are in close contact. Depending on the refractive index of prism and sample, the depth of light penetration into the sample, the measured spectra may differ. In addition, the measurement wavenumber range and durability vary depending on the prism material. The features of each prisms are shown below.
FT/IR-4600 FTIR spectrometer (left) and ATR PRO ONE ATR accessory (right)
Features of each prism
|Prism||RI (n1)||Penetration Depth dp*1
|RI of Sample (n2)*2
for Total Reflection
in Low Wavenumber*3
|ZnSe||2.4||Approx. 2.0 μm||1.7 or less||~500 cm-1|
|Diamond||2.4||Approx. 2.0 μm||1.7 or less||~350 cm-1 *4|
|Ge||4.0||Approx. 0.7 μm||2.8 or less||~550 cm-1|
|Suitable Sample||Non-Suitable Sample||Notes|
|Hard powder, acidalkaline,
|In case of hard
powder or hubbly
sample, diamond is
|Hard powder, General
|High RI sample||Poor S/N ratio in the
region around 2000
cm-1, due to internal
high RI sample
|Sample including carbon||Hard powder, acidalkaline||Weak absorption
due to small depth of
*3 Case of measurement using ATR PRO ONE and standard FTIR.
*4 If the measurement is needed in the wavenumber range below 350 cm-1, please contact local JASCO distributor.
Example: Diamond is suitable (Sample: Toluene)
Spectra measured with diamond and ZnSe ATR have higher peak intensities than measured with Ge ATR.
Measurements with diamond ATR can be extended down to the low wavenumber side.
Example: Ge is suitable (Sample: Carbon-containing rubber)
Spectra measured with Ge ATR has a flat baseline for a sample with a high refractive index and can be measured without distortion.
280AT0003-E, ATR, prism, diamond, Ge, ZnSe, refractive index
About the Author
Dr. Carlos Morillo received his Post Doc at Advanced Industrial Science & Technology in Fukuoka and was a Research Scientist at Kyushu University in Japan where he lived for several years. Carlos received his Doctor of Engineering from Kyushu University and his Masters and BS from Simon Bolivar University in Caracas Venezuela. He is an Applications Scientist at JASCO.