Microscope spectrophotometer

Fig. 2.17. Schematic layout of a microscope spectrophotometer system used to measure polarized absorption spectra of very small mineral crystals. The computer-operated, single-beam instrument shown here comprises a polarizing microscope equipped with a stabilized light source (xenon arc lamp or tungsten lamp cover the range 250-2000 nm), a modulator that chops the light beam with a frequency of 50 Hz (the amplifier for the photodetector signals is modulated with the same phase and frequency), and a Zeiss prism double monochromator. Single crystals as small as 10 ji.m diameter may be measured with this system. A diamond-windowed high-pressure cell can be readily mounted on the microscope scanning table for spectral measurements at very high pressures (after Burns, 1985, reproduced with the publisher s permission).

The microscope spectrophotometer system in routine use at the TRL is described in reference (7), so no details of the apparatus and its use are given here. Instead a brief description of the reason for developing and continually refining the microscope spectrophotometer facility will be presented. Historically the way to characterize a solid-state sample of a transplutonium element has been by standard X-ray powder diffraction analysis. When a systematic study of element 99, einsteinium, was undertaken, it was found that obtaining useful diffraction data from Es-containing materials was a very difficult, if not an impossible, task (22). The intensely radioactive Es-253 not only caused rapid blackening of the film used to record the diffraction pattern, but more importantly, it degraded the crystallinity of the sample. 

The procedure was as described (5/11/12). In short/ the absorption spectrum of a bleb suspension was measured/ and the overall extinction coefficients were calculated by dividing the absorbances by the total chlorophyll concentration. The absorption spectrum of single blebs was recorded in a Zeiss microscope spectrophotometer. The chlorophyll content of a bleb was estimated by fitting its spectrum to the overall extinction coefficients. Its membrane surface was calculated from its diameter/ and the specific surface was obtained as ratio of surface to chlorophyll content. 

It was shown that the measurement of the absorption spectrum of a single bleb in the microscope spectrophotometer is reproducible and free of artifacts (5,11,12). The absorption spectra of several patch free blebs with different diameters were measured for each preparation. In all cases the fit between spectra and overall extinction coefficient was as good as previously reported (5,11,12)... 

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. 

In order to overcome these problems, interest was focussed on that portion of the organic matter trapped in mineral precipitates which formed synchronously with sedimentation. In these cases, the material is hermetically sealed in the crystalline matter and may survive with relatively little subsequent alteration. Such preservation is common in cherts which are chemical precipitates of silica and now comist of fine grained quartz. These rocks offer the best chance for successful preservation of truely Precambrian molecular fossils. Modem microprobes and spectrophotometer microscopes allow the non-destructive analysis of organic matter enclosed in mineral crystals. Laser bombardment of microscopic... 

The products obtained are determined by the energy spectrum for the compositions, mainly for the Ca/P mole ratio, and characterized by infrared spectroscopy with the Fourier transformation intra-red spectrophotometer (FTIR) of Type Nicolet 51 OP made by Nicolet Co., thermal analysis on a thermo- gravimetric/differential thermal analyzer (TG/DTA) of Type ZRY-2P, X-ray diffraction (XRD) analysis with the X-ray diffractometer of Type XD-5 made by Shimadzu Co., scanning electron microscopy (SEM), and transmission electron microscopy (TEM) with the transmission electron mirror microscope of Type JEM-100SX type made by JEOL Co. 

The results of the characterization of the product synthesized with Fourier transformation infra-red spectrophotometer (FTIR), X-ray diffractometer (XRD), scanning electron mirror microscope (SEM) and the transmission electron mirror microscope (TEM) illustrate that the product synthesized by the process of double decomposition-precipitation with calcium nitrate and di-ammonium phosphate as the reactants in the SCISR consists of well dispersed particles of about 15 nm in diameter and 50-70 nm long, having a very regular shape and appearance and is confirmed to be hydroxylapatite. 

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. 

X-ray diffraction analysis of the samples is performed on a DRON-4 apparatus with Cr Ka radiation. As a monohromator, we applied a crystal of pyrolytic graphite. The carbon structure morphology is investigated with a REM-200 electron microscope. The infrared spectra of the optical transmission of the pressed sample tablet in KBr are measured on a Specord M80 spectrophotometer. 

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