Near infrared radiation spectroscopy spectrometers

There is a real chance of a breakthrough of Raman spectroscopy in routine analytics. Excitation of Raman spectra by near-infrared radiation and recording with interferometers, followed by the Fourier transformation of the interferogram into a spectrum -the so-called NIR-FT-Raman technique - has made it possible to obtain Raman spectra of most samples uninhibited by fluorescence. In addition, the introduction of dispersive spectrometers with multi-channel detectors and the development of several varieties of Raman spectroscopy has made it possible to combine infrared and Raman spectroscopy whenever this appears to be advantageous. 

A comprehensive historical review of the analytical applications of infrared spectroscopy from the first experiments to the introduction of FTIR spectrometers has appeared.221 The first study of the absorption of infrared radiation by a range of chemical substances was made in 1881 by Abney and Festing, after the former had developed a photographic method of detecting radiation in the near-infrared region. Over the next 25 years a number of other studies were made. This early phase culminated in the work of W. W. Coblentz in the United States, which was published in 1905.222 It became evident from Coblentz s data that infrared spectra were related to molecular structure, but IR spectroscopy remained principally the province of researchers in university physics departments until World War n. 

The first coupling of a LINAC with infrared spectroscopy has been performed by Palmese et al. in order to study in situ kinetics of radiation-induced cationic polymerization of epoxy systems. The aim of the study is to understand the curing behavior of polymers under irradiation. A UV light source and an electron beam (10 MeV pulse width of the beam from 2.5 to 10 pm) are coupled to a portable near infrared (NIR) instrument. Briefly, a portable NIR spectrometer (Control Development Incorporated, South Bend, IN, USA) is used,... 

In principle, Raman spectroscopy is a microtechnique [161) since, for a given light flux of a laser source, the flux of Raman radiation is inversely proportional to the diameter of the laser-beam focus at the sample, i.e., an optimized Raman sample is a microsample. However, Raman microspectroscopy able to obtain spatially resolved vibrational spectra to ca. 1 pm spatial resolution and using a conventional optical microscope system has only recently been more widely appreciated. For Raman microspectroscopy both conventional [162] and FT-Raman spectrometers [ 163], [ 164] are employed, the latter being coupled by near-infrared fiber optics to the microscope. 

In principle, all metallic elements can be determined by plasma emission spectrometry. A vacuum spectrometer is necessary for the determination of boron, phosphorus, nitrogen, sulfur, and carbon because the emission lines for these elements lie at wavelengths less than 180 nm, where components of the atmosphere absorb radiatjon. The usefulness for the alkali metals is limited by two difliculties (1) the compromise operating conditions that can be used to accommodate most other elements are unsuited for the alkalis, and (2) the most prominent lines of Li, K, Rb, and Cs are located at near-infrared wavelengths, which lead to detection problems with many plasma spectrometers that arc designed primarily for ultraviolet radiation. Because of problems of this sort, plasma emission spectroscopy is generally limited to the determination of about 60 elements. 

Raman and infrared spectra have also been compared for a series of 1,4-benzodiazepines, including diazepam (Vallium) and of closely related compounds [16,17]. The complementary nature of these two vibrational spectroscopic techniques was highlighted and the data provided spectral features that allowed identification of the drugs. The value of Fourier transform Raman spectroscopy using a near-infrared excitation source was also demonstrated for these heterocyclic molecules which have a tendency to fluoresce with visible radiation from conventional dispersive Raman spectrometers. 

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