Observation of a Penetration Depth Gradient in Attenuated Total Reflection Fourier Transform Infrared Spectroscopic Imaging Applications

Wessel, Elke; Heinsohn, G.; Schmidt-Lewerkuehne, Hartmut; Wittern, Klaus-peter; Rapp, Claudius; Siesler, Heinz W.

doi:10.1366/000370206779321391

Cited by 14 publications

(9 citation statements)

References 46 publications

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“…When performing quantitative studies it is important to note that even when analyzing a homogeneous sample the absorbance may not always be homogeneous throughout the whole imaged area of the sample. This is because the angle of incidence may not always be uniform across the imaging surface of the crystal [46]. This will have the effect of changing the effective path length and consequently the absorbance.…”

Section: Quantitative Analysismentioning

confidence: 99%

Applications of FTIR Spectroscopic Imaging in Pharmaceutical Science

Kazarian

Wray

2010

Raman, Infrared, and Near‐Infrared Chemical Imaging

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Section: Quantitative Analysismentioning

confidence: 99%

Applications of FTIR Spectroscopic Imaging in Pharmaceutical Science

Kazarian

Wray

2010

Raman, Infrared, and Near‐Infrared Chemical Imaging

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“…Apart from focusing, it is also important to ensure that there is no change in the depth of penetration across a large field of view. Unlike the previous work, in which a hemispherical ATR crystal 19 or FastIR accessory 28 was used, which causes a change in the depth of penetration across the imaging area, the angle of the IR beam is not expected to change significantly when the inverted prism ATR crystal is moved in the x-or yaxis because the surface where the IR beam enters the crystal is flat, so the depth of penetration is expected to remain constant. Nevertheless, an image of pure paraffin oil placed on the measuring surface of the ZnSe crystal has been obtained.…”

Section: Resultsmentioning

confidence: 90%

Attenuated Total Reflection—Fourier Transform Infrared Imaging of Large Areas Using Inverted Prism Crystals and Combining Imaging and Mapping

Chan

Kazarian

2008

Appl Spectrosc

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Attenuated total reflection-Fourier transform infrared (ATR-FT-IR) imaging is a very useful tool for capturing chemical images of various materials due to the simple sample preparation and the ability to measure wet samples or samples in an aqueous environment. However, the size of the array detector used for image acquisition is often limited and there is usually a trade off between spatial resolution and the field of view (FOV). The combination of mapping and imaging can be used to acquire images with a larger FOV without sacrificing spatial resolution. Previous attempts have demonstrated this using an infrared microscope and a Germanium hemispherical ATR crystal to achieve images of up to 2.5 mm x 2.5 mm but with varying spatial resolution and depth of penetration across the imaged area. In this paper, we demonstrate a combination of mapping and imaging with a different approach using an external optics housing for large ATR accessories and inverted ATR prisms to achieve ATR-FT-IR images with a large FOV and reasonable spatial resolution. The results have shown that a FOV of 10 mm x 14 mm can be obtained with a spatial resolution of approximately 40-60 microm when using an accessory that gives no magnification. A FOV of 1.3 mm x 1.3 mm can be obtained with spatial resolution of approximately 15-20 microm when using a diamond ATR imaging accessory with 4x magnification. No significant change in image quality such as spatial resolution or depth of penetration has been observed across the whole FOV with this method and the measurement time was approximately 15 minutes for an image consisting of 16 image tiles.

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“…The noise at the left edge of the image measured with the aperture at the bottom of the lens is due to the weak illumination by IR light in those areas, which does not affect other areas of the image. A spread of angles of incidence over the imaging area could be a concern 22 when using a particular optical accessory with limited flexibility to be perfectly aligned. The lack of the absorbance gradient shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Chemical Imaging with Variable Angles of Incidence Using a Diamond Attenuated Total Reflection Accessory

Chan

Tay²,

Poulter³

et al. 2008

Appl Spectrosc

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A new development in Fourier transform infrared (FT-IR) imaging using a diamond attenuated total reflection (ATR) imaging accessory in a novel manner that allows the angle of incidence to be varied in order to obtain images from subsurface layers of different thickness is introduced. Chemical images of samples from the same area but with different depths of penetration are obtained by changing the angle of incidence as well as using different spectral bands at different wavenumbers. Changes in the angle of incidence with this accessory were made possible by taking advantage of the relatively large numerical aperture employed by the original imaging optics. This arrangement allowed us to introduce an additional movable aperture in the optical design to restrict the angle of incidence to certain values. Two samples have been studied, one for the calibration of the angle of incidence while the other demonstrates the capability of obtaining three-dimensional (3D) information using this approach. Advantages of this new approach include the relatively high spatial resolution (it can spatially resolve features as small as 12 mum without a microscope) and no change in the imaging area and sampling area during manipulation of the angle of incidence.

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Observation of a Penetration Depth Gradient in Attenuated Total Reflection Fourier Transform Infrared Spectroscopic Imaging Applications

Cited by 14 publications

References 46 publications

Applications of FTIR Spectroscopic Imaging in Pharmaceutical Science

Applications of FTIR Spectroscopic Imaging in Pharmaceutical Science

Attenuated Total Reflection—Fourier Transform Infrared Imaging of Large Areas Using Inverted Prism Crystals and Combining Imaging and Mapping

Chemical Imaging with Variable Angles of Incidence Using a Diamond Attenuated Total Reflection Accessory

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