FTIR Imaging Instrumentation

An optimal coupling between an IRSR source and FTIR imaging instrumentation equipped with small FPA detectors may push the established limits of FTIR imaging towards a real time imaging of single-cell phenomena. 

In principle, operation of the FTIR microspectroscopy is the same as for a conventional FTIR instrument except the spectrum is obtained from a microscopic area or intensity distribution is mapped in the sample plane. A spectrum from an area in the order of 10 x 10 /im can be obtained. Mapping or FTIR imaging at micro-level resolution can be achieved by scanning a sample using a motorized sample stage. The resolution is primarily determined by the size of the focused IR beam and precision of motorized stage. Reflectance microspectroscopy is more widely used than the transmittance mode in FTIR microscopy because minimal sample preparation is required. 

Figure 4.11 The SpectraView spectral imaging instrument from Applied Spectral Imaging and the FTIR. spectral imaging system from Varian (Reproduced by permission of Applied Spectral Imaging and Varian Inc.).

Figure 4.75 Use of FTIR imaging, (a) The visible light image of an inclusion in polypropylene film. Sample size is approximately 450 x 450 p,m. (b) The IR image of the same inclusion showing the distribution of a carbonyl contaminant through the inclusion. The image contains more than 5000 spectra at 6.25 p,m pixel size. The total data collection time was 90 s. Collected on a Spectrum Spotlight 300 FT-IR Imaging System. [Courtesy of PerkinElmer Instruments, Shelton, CT (www.perkinelemer.com).]...

Other uses of an IR microscope in forensic analysis include the examination of fibers, drugs, and traces of explosives. For example, oxidation of hair can occur chemically or by sunlight oxidation of cystine to cysteic acid can be seen in hair fibers by FTIR microscopy (Robotham and Izzia). Excellent examples in full color of FTIR imaging microscopy can be found on the websites of companies like PerkinElmer and Thermo Fisher Scientific. Our limitations in use of gray scale make many of the examples unsuited for reproduction in the text. A novel IR microscope combined with atomic force microscopy, the nanoIR platform from Anasys Instruments (www.anasysinstruments.com), permits nanoscale IR spectroscopy, AFM topography, nanoscale thermal analysis, and mechanical testing. 

There are a number of approaches to allow infrared microspectroscopic investigations of polymers. While interferometer based approaches dominate the instrumentation in general, other approaches may be effective in specihc cases or when dedicated instrumentation examining a limited range of problems is desired. FPAs, employed to achieve spatial discrimination as in FTIR imaging or spatial and spectral discrimination as in dispersive and hlter approaches, provide flexibility and faster spectroscopy due to their multichannel detection advantage. Many new approaches to microspectroscopy are dedicated to achieving spatial resolution better... 

Because they can precisely measure wavelengths, FTIR spectrometers permit spectra and file storage using an instrument form at and certain rules so that spectra can be treated by instruments from other manufacturers. Each data point in the spectrum can be stored as an ACSII file. However, the software normalises the raw data and lowers the spectral resolution to obtain fewer calculated values (one point every 8 or 4 cm-1 - giving less than 1 Koctet/spectrum). The inverse operation can be used to give a proper corrected image of the spectrum. 

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