Forensic Instruments : ATR-FTIR

ATR-FTIR
Mid-Infrared (IR) spectroscopy is an extremely reliable and well recognized fingerprinting method.
Strengths of IR spectroscopy is its ability to obtain spectra from a very wide range of solids, liquids and gases.The technique of Attenuated Total Reflectance (ATR) has in recent years revolutionized solid and liquid sample analyses because it combats the most challenging aspects of infrared analyses, namely sample preparation and spectral reproducibility.

PRINCIPLE OF ATR-FTIR

• Operates by measuring the changes that occur in a totally internally reflected Infrared beam.
• Infrared beam is directed onto an optically dense crystal with a high refractive index  at a certain angle.
• This internal reflectance creates an evanescent wave that extends beyond the surface of the crystal into the sample held in contact with the crystal.
• Imagine evanescence wave as a bubble of infrared that sits on the surface of the crystal.
• This evanescence wave  protrudes only a few microns (0.5µ – 5µ) beyond the crystal surface and into the sample.
• In regions of the IR spectrum, sample absorb energy, the evanescent wave will be attenuated or altered.
• The attenuated energy from each evanescent wave is passed back to the IR beam, which then exits the opposite end of the crystal and is passed to the detector.

Advantages

• Faster sampling
• Improving sample-to-sample reproducibility
• Minimizing user-to-user spectral variation
• Higher quality spectral databases for more precise material verification and identification

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