IR microscope

Sample preparation is straightforward for a scattering process such as Raman spectroscopy. Sample containers can be of glass or quartz, which are weak Raman scatterers, and aqueous solutions pose no problems. Raman microprobes have a spatial resolution of - 1 //m, much better than the diffraction limit imposed on ir microscopes (213). Eiber-optic probes can be used in process monitoring (214). 

The resolution of infra-red densitometry (IR-D) is on the other hand more in the region of some micrometers even with the use of IR-microscopes. The interface is also viewed from the side (Fig. 4d) and the density profile is obtained mostly between deuterated and protonated polymers. The strength of specific IR-bands is monitored during a scan across the interface to yield a concentration profile of species. While in the initial experiments on polyethylene diffusion the resolution was of the order of 60 pm [69] it has been improved e.g. in polystyrene diffusion experiments [70] to 10 pm by the application of a Fourier transform-IR-microscope. This technique is nicely suited to measure profiles on a micrometer scale as well as interdiffusion coefficients of polymers but it is far from reaching molecular resolution. 

The first linkage between a microscope and an IR spectrophotometer was reported in 1949 [15]. Today, every manufacturer of IR spectrophotometers offers an optical/IR microscope sampling accessory. The use of optical and IR microscopy is a natural course of action for any solid state investigation. Optical microscopy provides significant information about a sample, such as its crystalline or amorphous nature, particle morphology, and size. Interfacing the microscope to an IR spectrophotometer ultimately provides unequivocal identification of one particular crystallite. Hence, we have the tremendous benefit of IR microscopy for the identification of particulate contamination in bulk or formulated drug products. 

FT-IR microspectroscopy is a new nondestructive, fast and rehable technique for solid-phase reaction monitoring. It is the most powerful of the currently available IR methods as it usually requires only a single bead for analysis, thus it is referred to as single bead FT-IR [166]. (See also Chapter 12 for further details). The high sensitivity of the FT-IR microscope is achieved thanks to the use of an expensive liquid nitrogen-cooled mercury cadmium telluride (MCT) detector. Despite the high cost of the instrument, this technique should become more widely used in the future as it represents the most convenient real-time reaction monitoring tool in SPOS [166, 167]. 

ATR FT-IR spectroscopy allows for analysis of the polymer surface, rather than the bulk of the sample. Whereas the spectra obtained from the FT-IR microscope and BCA are recorded in transmittance mode and are used to analyze the entire bead, an ATR objective can be brought into direct contact with the sample in order to yield information about the chemistry taking place mainly on the periphery of the bead. Some FT-IR microscopes are equipped with an ATR crystal, and ATR analysis can be achieved on a single bead [172], but there have been no reports of automated ATR instruments. This technique has been used in kinetic studies, to prove that the esterification of Wang resin (4) (Scheme 1.4) to give the corre-... 

Validation of Vibrational Imaging Protocols with IR Microscopic Imaging... 

IR spectra were measured by Bruker IFS-113v IR Fourier spectrometer transition spectra and diffuse reflection at T = 295 K. IR microscope of the Fourier spectrometer was used for the measurements of the transmission spectra in the spectral range 600-9,000 cm-1 Transmission spectra of the thin films were also measured in the spectral range from 4,000 to 18,000 cm-1 using a standard doublebeam spectrometer. 

IR transmission spectra (T) of the thin polycrystalline specimens or powders were measured using IR microscope of the Fourier-spectrometer at room temperature in the spectral range of 600 5,000 cm-1. Optical absorption spectra were calculated as -ln(T). Figure 11.11 demonstrates normalized absorption spectra of fulleranes C60Hx with x = 36, 42, 48 and 60 together with the well known spectrum of fullerit... 

Figure 1.4 Layout and principle of operation of IR microscopes when single-channel detectors are employed (top) and when multichannel detectors are employed (bottom). Single-channel detection requires the use of apertures. Multichannel detectors typically range from a linear 16-element detector to large 65 536-element (256 x 256) detectors.

Spragg, R., Hoult, R. and Sellers, J. (2002) Comparing near-IR and mid-IR microscopic reflectance FT-IR imaging. Presented at the Federation of Analytical Chemists and... 

In this section, we outline the applications of IR microscopic imaging to the molecular level determination of dermal and transdermal percutaneous absorption. The rationale for these experiments is that drugs often exhibit low penetration rates... 

Three advantages of IR microscopic imaging for the studies of permeation into skin are clear from the above data. First, the location of exogenous material is directly monitored. Second, conformation-sensitive spectral features provide useful indicators of changes in molecular structure. Third, if the exogenous material perturbs the molecular structure of the native skin components, the nature and locahon of the disruption can be imaged directly from the spectra of the endogenous material. 

IR analysis of particulate coal do not occur with the thin section samples used in this work which have highly uniform thicknesses. However, a related problem resulting from the convergent beam of the IR microscope can occur and is described below. 

Because the thin section specimens are not contaminated with adhesives or embedding materials, and because the samples are readily accessible on the stage of the IR microscope, this technique is well suited for in situ" treatments of the coal. Alternatively, since the 15 micrometer thick specimens of coal can ordinarily be handled and transported without damage (if proper care is taken), an untreated sample can be initially analyzed, then it can be removed from the instrument for chemical or thermal treatment, and finally, the same specimen can be returned to the microspectrometer for determination of the changes in the IR spectrun. The analysis of the same specimen before and after treatment is highly desirable for micro-heterogeneous substances such as coals. 

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