IR-PLAN microscope

All infrared spectra were recorded with an IR-PLAN microscope (IR-PLAN is a registered trade mark of Spectra Tech, Inc.) integrated to a Perkin-Elmer Model 1800 Fourier transform infrared (FT-IR) spectrophotometer. The spectrophotometer consisted of a proprietary heated wire source operated at 1050°C, a germanium overcoated potassium bromide beamsplitter, and a narrow-band mercury-cadmium-telluride (HgCdTe) detector. The detector was dedicated to the microscope and had an active area of 250 x 250 pm. The entire optical path of the system microscope was purged with dry nitrogen. 

The spatial resolution of FT-IR microspectroscopy, without sacrificing spectral quality and resolution, makes imaging possible. Shortly after the introduction of the first research-quality IR microscope by Messerschmidt and Sting in 1986, Wetzel, Messerschmidt and Fulcher reported spectra obtained from wheat kernel transverse sections in situ, and compared them with flour milling fractions [7]. This was achieved with an accessory IR-PLAN microscope optically interfaced to a Nicolet interferometer bench. Subsequently, at the Agriculture Canada laboratory the same model IR-PLAN was interfaced to a Bomen Michelson IR 100 spectrometer such that, over the period of a year, transverse sections of wheat kernels, vanilla beans, peppercorns and soybeans were manually line-mapped to reveal any differences in microchemical structural characteristics between their different botanical parts [8]. 

In studies conducted at Norwich by Sene and coworkers [67], a BioRad FTS-40 FT-IR instrument interfaced to a Spectra-Tech IR PLAN microscope was used, with sample areas of 100 x 100 pm. The operation was conducted in transmission mode on Bap2 windows, and the spot size used was compatible with areas of the single cell waU fragments of 0.1-0.2 pm thickness. Pectic polysaccharides extracted... 

Figure 2 (A) Fourier transform IR spectrometer with (B) Spectratech IR plan microscope attachment. (C) Infrared spectrum from a singie poiyester fiber measured by using the Spectratech iR pian microscope.

The microscope (SpectraTech model IR-Plan) is a research-grade optical microscope modified for application in the IR spectral range. Focusing is accomplished by Cassegrainian-type mirrors. Optical and IR beam paths are collinear and switched by tilting mirrors. Thus, samples may be characterized and selected visually before recording IR spectra. 

The IR-PLAN was patented in 1989 [3] and designed as an attachment for any commercial FT-IR instrument. Subsequently, other manufacturers provided similar peripheral microscopes for the same purpose with, in each case, an optical... 

For the FTIR microscopic diffusion measurements (micro-FTIR spectroscopy) [30-32] the same Perkin-Elmer 1800 spectrometer was used, but a so-called IR microscope (Spectra Tech model IR-Plan) and an appropriate flow-through micro-cell were attached (see Figures 4a,b). 

Figure 4.38. (a) IR ATR microscopic spectra of clean hair (solid line) and hair-sprayed hair (dashed line), (b) Difference specfrum (solid line) and reference spectrum of poly(vinylacefafe) (dashed line). Spectra were measured with Nic-Plan microscope interfaced to Magna-IR (Nico-let Instrument Corp.) FTIR spectrometer. Sixty-four sample scans at resolution of 8cm were coadded and rationed against 64 background scans. Reprinted, by permission, from P. A. Martoglio, Nicolet Application Note, AN-9694, Nicolet Instrument, Madison, 1997. Copyright Nicolet Instrument Corp. 

Some of the new IR microscopes on the market are capable of minimising these problems. An IR-Plan IR microscope (obtained from Spectra-Tech, Stamford, CT) has been used to obtain IR spectra of Kevlar filaments and also to carry out orientation measurements. The microscope uses a 15x IR/visible reflecting lens with Cassegrain optics to focus the IR beam onto the sample (Refleachromat, Spectra-Tech). A lOx reflecting Cassegrain beam condenser is used to collect the transmitted beam after it passes through the sample. The beam condenser also has a sample compensator, which can be used to correct for optical aberrations caused by the fibre samples. The microscope uses its own narrow band liquid... 

Figure 3. Diagram of the Spectra Tech IR-PLAN FT-IR microscope.

The first demonstration of FT-IRM with a synchrotron IR source was made during the early 1990s, when a custom-built IR microscope was installed at the National Synchrotron Light Source (Upton, NY, USA) [16,17], while similar efforts were underway at UVSOR in Japan at the same time [18]. The first commercial IR microscope was installed at the NSLS a few years later [10, 19]. Since then, IR microscopes have been installed on over 15 beamlines at synchrotrons worldwide, and an equal number are currently in the planning or construction stages. 

Teams working at synchrotron IR beamlines all around the world have installed and tested or are going to install array detectors on their IR microscope end-stations. The scenario is changing continuously, and many facilities with IR microspectroscopy beamlines are planning the installation of mid-IR arrays in the near future. 

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