Macro FT-IR imaging

If a larger field of view is required, the macrochamber IMAC is used instead of the microscope. This consists of an optical and a sample compartment, with con- 

Figu re 9.5 Available accessories for the imaging macrochamber, (a) Transmission (Broker Optik GmbH, Ettlingen, Germany) (b) Reflection (Pike Technologies, Madison, USA) (c) ATR with a ZnSe crystal (Harrick Scientific Products inc.. New York, USA). 

The imaging area for transmission and reflection measurements is consistent with the detector size (3.9 x 3.9mm ). For ATR-measurements, the imaging area is 3.9 X 5.5 mm because of the illumination geometry [37]. 

Usually, there is only one FPA detector available, and the position of the FPA detector must be interchanged between the microscope and the macrochamber. 

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The color-coded classification results obtained, using the SIMCA and LDA models for five specimens, are shown in Figure 3.8. Four tissue sections were prepared on CaF2 substrates from different brain metastases, while a normal brain specimen was obtained from an autopsy. The images were acquired using a FT-IR imaging system coupled to a 64 x 64 FPA detector (Bruker). The field of view in the macro chamber (IMAC) was 4 x 4mm and the resolution of 62 xm per pixel was sufficient to identify the molecular information of the main tissue classes. 

ATR-FT-IR Imaging for Pharmaceutical and Polymeric Materials From Micro to Macro Approaches... 

There is a general belief that pressure must always be applied to a sample in order to obtain its FT-IR image in the ATR mode. Whilst it is important to ensure homogeneous contact between the sample and the ATR crystal, such that the image would not represent only the quality of the contact, there is often no need to apply pressure in this situation. Examples in macro ATR imaging include the swelling pharmaceutical tablets or biomedical tissues, whereby a good and repro-... 

In this chapter, we have presented some of the recent developments and applications of ATR-FT-IR imaging to pharmaceutical samples and polymeric materials. The use of both micro and macro modes in ATR-FT-IR imaging has been discussed. Imaging in the ATR mode may be very versatile, and offers imaging with different spatial resolution and different fields of view. It is important to remember that ATR imaging provides information only about that layer of the sample which is adjacent to the surface of the ATR crystal, and that the thickness of this layer may range from a fraction of a micrometer to several micrometers. However, the opportunity exists to obtain chemical images from layers of different thickness in... 

The applicability of ATR FT-IR imaging ranges from micro-ATR imaging using a Ge microscope objective to the use of ATR accessories with focused or expanded optics without recourse to the microscope [3]. Thus, the range of areas in the samples that could be measured simultaneously using FPA detectors and a prismshaped ATR crystal is from 500 pm X 700 pm to 1.6 cm X 2.1 cm (see Section 9.2.3 for further discussion). The measured area with macro-ATR imaging depends on the specific optics used in these ATR accessories and also on the size of the pixels in the array detector. Most of the currently used detectors have a pixel size of 40 pm X 40 pm or 60 pm x 60 pm. 

Overview of ATR FT-IR Imaging Approaches Micro (Ge), Macro (Diamond, Si), Expanded FOV (ZnSe), Variable Angle... 

Kazarian SG, Chan KLA, Tay FH. ATR-FT-IR Imaging for Pharmaceutical and Polymeric Materials From Micro to Macro Approaches. In Salzer R, Siesler HW, editors. Infrared and Raman Spectroscopic Imaging. Germany Wiley-VCH 2009, p 347-375. 

Macro ATR-FT-IR approach included the imaging of many different pharmaceutical formulations under a controlled environment, as well as simultaneous studies of the dissolution of several formulations in separate microchannels [33]. 

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