CCD-Raman spectrometry

With such an obvious advantage of sensitivity to CCD-Raman spectrometers, we must ask why FT-Raman spectrometers have found their place in the marketplace. The answer is found in one word— fluorescence The shot noise introduced by fluorescence is so great that it offsets the sensitivity advantage of CCD-Raman spectrometers. Unlike the case for CCD-Raman spectrometry, fluorescence-free Raman spectra can usually be measured with a Fourier transform spectrometer in 5 or 10 minutes from almost any type of sample. 

In the second application, it was shown that softwoods and hardwoods could be distinguished through their FT-Raman spectra [14]. All the woods were colored to a greater or less extent, and useful spectra could not be obtained by CCD-Raman spectrometry, even with 782-nm excitation. Representative spectra are shown in Figure 18.11. Even when 1064 nm was used, there was a relatively weak background caused by fluorescence and the spectra shown in Figure 18.11 were obtained after baseline correction. 

FT Raman spectrometry, which was needed because the Raman spectrumgenerated 1064 nm radiation was at too long a wavelength for silicon-based CCD detectors. 

For these reasons, analytical Raman spectrometry has undergone a remarkable rebirth since about 1985. Instruments based on Fourier transform techniques and CCD array detectors are commercially available from a large number of vendors in North America, Europe, and Asia. Like infrared spectrometry, Raman spectrometry has outlived its seventh age, although whether it has matured through its second childhood yet is debatable. Nonetheless, Raman spectrometry is still a vital weapon in a vibrational spectroscopist s arsenal. 

In light of the fact that Fourier transform instrumentation was largely responsible for expanding Raman spectroscopy into the analytical laboratory, it is perhaps interesting to consider why Raman spectroscopy is so popular today but Fourier transform Raman does not play the dominant role. After a discussion of the poor sensitivity of NIR Raman spectrometry using a scanning monochromator with PMT detection in Section 18.1, it was stated To improve this situation, either a multichannel or multiplex measurement was needed and the multiplex measurement came first. Multichannel measurements came very shortly afterward, however, and instruments based on polychromators with silicon-based charge-coupled-device (CCD) array detectors have become more popular than FT-Raman spectrometers. In this section we compare the performance of FT- and CCD-Raman spectrometers. 

Developments such as Fourier Raman spectrometry and the charge-coupled device (CCD) detector enhance the usefulness of Raman spectroscopy for fluorinated surfactants. 

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