atr原理.pdf

ATR_AN_3pg_6_1 6/17/05 4:05 PM Page 1
A PPLICATION N OTE
ATR – Theory and Applications
Attenuated Total Reflectance (ATR) is today the most widely used While the analysis of samples by ATR is easy, it is interesting
FTIR sampling tool. ATR generally allows qualitative or quantitative and useful to be aware of each of the following experimental
analysis of samples with little or no sample preparation which factors and how they affect the final spectrum:
greatly speeds sample analysis. The main benefit of ATR sampling • Refractive indices of the ATR crystal and the sample
comes from the very thin sampling path length and depth of
• Angle of incidence of the IR beam
ration of the IR beam into the sample. This is in contrast to
• Critical angle
traditional FTIR sampling by transmission where the sample must
be diluted with IR transparent salt, pressed into a pellet or pressed to • Depth of ration
a thin film, prior to analysis to prevent totally absorbing bands in • Wavelength of the IR beam
the infrared spectrum. • Effective path length
parison of transmission Vs ATR sampling results for a • Number of reflections
thick polymer sample is shown below where the sample is too
• Quality of the sample contact with ATR crystal
thick for high quality transmission analysis (shown in the lower
blue spectrum). In transmission spectroscopy, the IR beam passes