AOTF Spectrometers

Some types of the described spectrometers can be applied for NIR imaging purposes. FT-NIR and AOTF imaging spectrometers are already available on the market. 

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Figure 9.2. Spectrum of benzene obtained with AOTF spectrometer of Figure 9.1 (Adapted from Reference 9, with permission.)...

In one paper by Kirsch and Drennen [62], three experiments were performed on coated tablets. In the first experiment, intact theophylline tablets coated with an ethylcellulose polymer were analyzed by acousto-optic tunable filter (AOTF) spectrometers. Tablets were coated with increasing levels of ethylcellulose to vary the dissolution profiles. After spectra were collected, the dissolutions were run on a U.S.P. Type II dissolution apparatus. The time required for 50% of the drug to enter solution was used as the measure of dissolution rate. Principal component (PC) regression was used to develop the calibration. This gave a SEE of 2.8 min, a coefficient of variation of 0.977, and a SEP of 6.6 min the time to 50% dissolution ranged from 48 to 93 min. 

DEVELOPMENT OF MINIATURE ACOUSTO OPTIC TUNABLE FILTER (AOTF) SPECTROMETER FOR DETECTION OF TOXIC INDUSTRIAL... 

Keywords. Toxic Industrial Chemicals AOTF spectrometer. 

The fiber optic AOTF spectrometer is divided into several subsystems - collection optics, optical fiber, collimating optics, AOTF, detector system, driving electronics, and data acquisition. 

Collection Optics The AOTF spectrometer is an active detection system. The collection optics couples reflected source light by the surface materials into an optical fiber or fiber bundle, which convey the optical signal to the AOTF. 

An acousto-optical tunable filter is a specialized optic whose bandpass is determined by the radio frequency applied across the optic. AOTF spectrometers are full-spectrum instruments. 

AOTF. An acousto-optical tunable filter (AOTF) (53) is a radio frequency (RF)-controlled narrow-band interference filter. Figure 4.1.10 is a schematic of a typical AOTF spectrometer. Most contemporary AOTF crystals are tellurium dioxide (TeOa)... 

Figure 4.1.10. Schematic of a AOTF spectrometer. The major advantage of AOTF is the snap-to feature that allows the immediate and random isolation of specific wavelengths. This means that once the calibration wavelengths are determined the wavelengths can be read without scanning all wavelengths.

Infrared Fiber Systems, Inc. 2301-A Broadbirch Dr. Silver Spring, MD 20904 USA TEL 301-622-9546 FAX 301-622-7135 Email info infraredfiber systems.com Optical fibers, laser windows, AOTF spectrometers... 

FTIR in combination with a cone calorimeter or in relation to various Are smoke toxicity tests has considerable potential for on-line analysis of Are gases from burning rubbers and plastics [110]. Kowol et al. [68] have reported the use of a FTIR-AOTF spectrometer for rapid identification of black plastics from automotive construction. In the wavelength region between 2.5 and 4 /u.m (where the fundamentals of the CH- and NH-stretching vibrations... 

Secondly, NIR spectrometers are often used for practical or routine purposes. Spectrometers developed for such purposes should, therefore, ideally be (i) portable, small in size, and light in weight, (ii) capable of use under severe conditions such as at high or low temperatures, in dusty places, or with mechanical disturbances, and (iii) inexpensive. Since FT-NIR spectrometers cannot fiilly satisfy these conditions, various other types of spectrometers have been developed and used. A dispersive spectrometer with a multichannel detector can be used under the conditions with mechanical disturbances because it has no moving mechanism such a spectrometer can be installed, for example, on a rotary blender of powdered dmgs. On the other hand, spectrometers with optical filters and AOTF spectrometers, which are light in weight and inexpensive, are suitable for outdoor in-the-field type measurements. 

In the rest of this section, spectrometers with optical Alters and AOTF spectrometers, which are seldom used in the other wavelength regions, are briefly described. 

The wavelength resolution and reproducibility of current AOTF spectrometers seem to be inferior to those of FT spectrometers but if these could be improved technically, a high-performance AOTF spectrometer may be realized in the future. 

Figure 18.3 Schematic illustration of an AOTF spectrometer in the arrangement for measuring diffuse reflection.

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