179:, with the exact value determined by the wavelength of light, the angle of incidence and the indices of refraction for the ATR crystal and the medium being probed. The number of reflections may be varied by varying the angle of incidence. The beam is then collected by a detector as it exits the crystal. Most modern infrared spectrometers can be converted to characterise samples via ATR by mounting the ATR accessory in the spectrometer's sample compartment. The accessibility, rapid sample turnaround and ease of use of ATR with
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as aqueous solutions. For ultraviolet or visible light (UV/Vis) the evanescent light path is sufficiently short such that interaction with the sample is decreased with wavelength. For optically dense samples, this may allow for measurements with UV. Also, as no light path has to be established single shaft probes are used for process monitoring and are applicable in both the near and mid infrared spectrum.
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258:, allowing the macromolecule to be anchored to a lipid bilayer, which is attached to a Germanium crystal or other suitable optical media. Internal reflection with and without applied pharmaceutical or ligand will produce difference spectra to study conformational changes of the proteins upon binding.
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Infrared (IR) spectroscopy by ATR is applicable to the same chemical or biological systems as the transmission method. One advantage of ATR-IR over transmission-IR is the limited path length into the sample. This avoids the problem of strong attenuation of the IR signal in highly absorbing media such
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than the sample being studied. Otherwise light is lost to the sample. In the case of a liquid sample, pouring a shallow amount over the surface of the crystal is sufficient. In the case of a solid sample, samples are firmly clamped to ensure good contact is made and to remove trapped air that would
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flows of aqueous solutions by engineering microreactors with built-in apertures for the ATR crystal, allowing the flow within microchannels to pass across the crystal surface for characterisation, or in dedicated flow cells. Due to the ATR geometry and the resulting evanescent wave, it is possible
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is passed through the ATR crystal in such a way that it reflects at least once off the internal surface in contact with the sample. This reflection forms the evanescent wave which extends into the sample. The penetration depth into the sample is typically between 0.5 and 2
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reduce signal intensity. The signal to noise ratio obtained depends on the number of reflections but also on the total length of the optical light path which dampens the intensity. Therefore, a general claim that more reflections give better sensitivity cannot be made.
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with this technique to study transport phenomena and sorption kinetics through thin films. The ability to passively characterise samples, with no sample preparation has also led to the use of ATR-FTIR in studying
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band between 2600 and 1900 cm significantly decreases signal to noise in this region. The shape of the crystal depends on the type of spectrometer and nature of the sample. With
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spectrometers, the crystal is a rectangular slab with chamfered edges, seen in cross-section in the illustrations. Other geometries use prisms, half-spheres, or thin sheets.
370:
Minnich, Clemens B. (2010). "Determination of the
Dispersion Characteristics of Miniaturized Coiled Reactors with Fiber-Optic Fourier Transform Mid-infrared Spectroscopy".
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ATR-FTIR is also used as a tool in pharmacological research to investigate protein/pharmaceutical interactions in detail. Water-soluble proteins to be investigated require
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F. M. Mirabella, Jr., Practical
Spectroscopy Series; Internal reflection spectroscopy: Theory and applications, Marcel Dekker, Inc.; Marcel Dekker, Inc., 1993, 17-52.
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Jesse
Greener, Bardia Abbasi, Eugenia Kumacheva, Attenuated total reflection Fourier transform spectroscopy for on-chip monitoring of solute concentrations
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Light undergoes multiple internal reflections in the crystal of high refractive index, shown in yellow. The sample is in contact with the crystal.
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Carter, Catherine F. (2010). "ReactIR Flow Cell: A New
Analytical Tool for Continuous Flow Chemical Processing".
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make it an ideal material for ATR, particularly when studying very hard solids, although the broad diamond
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399:"A FTIR–ATR study of liquid diffusion processes in PET films: comparison of water with simple alcohols"
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This evanescent effect only works if the crystal is made of an optical material with a higher
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430:"Surface-Attached Polyhistidine-Tag Proteins Characterized by FTIR Difference Spectroscopy"
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Northwestern
University Atomic and Nanoscale Characterization Experimental Center
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Pinkerneil, Philipp; Güldenhaupt, Jörn; Gerwert, Klaus; Kötting, Carsten (2012).
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288:"FT-IR Spectroscopy—Attenuated Total Reflectance (ATR)"
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which enables samples to be examined directly in the
397:Sammon, C.; Yarwood, J.; Everall, N. (March 2000).
128:) is a sampling technique used in conjunction with
49:. Unsourced material may be challenged and removed.
505:"Fourier Transform Infrared Spectroscopy (FT-IR)"
372:Industrial & Engineering Chemistry Research
210:is ideal for use in the Far-IR region of the
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194:Typical materials for ATR crystals include
345:Organic Process Research & Development
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295:Perkin Elmer Life and Analytical Sciences
214:. The excellent mechanical properties of
109:Learn how and when to remove this message
16:Infrared spectroscopy sampling technique
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181:Fourier transform infrared spectroscopy
238:Recently, ATR-IR has been applied to
155:An ATR accessory for IR spectroscopy.
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47:adding citations to reliable sources
140:state without further preparation.
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483:Internal Reflection Spectroscopy
333:, Lab Chip, 10 (2010) 1561-1566.
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34:needs additional citations for
58:"Attenuated total reflectance"
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415:10.1016/S0032-3861(99)00405-X
122:Attenuated total reflection
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487:John Wiley & Sons Inc
268:Surface plasmon resonance
161:total internal reflection
212:electromagnetic spectrum
509:nuance.northwestern.edu
159:ATR uses a property of
481:Harrick, N.J. (1967).
446:10.1002/cphc.201200358
297:. 2005. Archived from
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