Quantitation optical trains

The optical train employed for photometric determinations of fluorescence depends on the problem involved. A spectral resolution of the emitted fluorescence is not necessary for quantitative determinations. The optical train sketched in Figure 22B can, therefore, be employed. If the fluorescence spectrum is to be determined the fluorescent light has to be analyzed into its component parts before reaching the detector (Fig. 28). A mercury or xenon lamp is used for excitation in such cases. 

Unhke visual evaluation of a chromatograms before derivatization, which can only give quahtative or semiquantitative results, direct optical evaluation using instruments enables quantitative results to be obtained. For this, a traditional TLC scanner, diode-array scanner or video equipment, either alone or in combination with a flat-bed scanner, is used. Quantitative evaluation with these instruments is described in more detail in Sections 1.2-1 A. However, the limits of this book would be exceeded if we gave a detailed description of all the commercially available equipment that can be used to quantify substances on TLC plates. Training in the use of TLC scanners can be obtained in company seminars (e.g. CAMAG) and detailed instructions are provided by the manufacturer when the equipment is purchased. 

Already in the early days of optical pxunping spectroscopy it has been shown that modulated optical light can create atomic coherence between close lying atomic substates and therefore can be used to measure the energy splitting between these states [l]. In this context optical pvunping with a pulse train has often been mentioned but only scarcely applied for quantitative measurements. 

Pathology is employed in biomedicine to identify and characterize the disease state of human tissue, using well-established optical microscopy techniques [79]. Often, disease-state determination involves the analysis of thinly sectioned, stained biopsied tissue in order to visualize various disease-specific pathologic markers. Although these examinations are typically made by highly trained practitioners, the potential exists to make the determinations more quantitative and less reliant on subjective observations by integrating the efficacy of vibrational spectroscopy with optical microscopy. This section describes... 

In combination with full-spectrum multivariate analysis methods and developments in fibre-optic technology NIR has gained great importance especially for chemical quality assurance but also for automatic reaction process confiol of polymers, in a rational and economical manner [272,278]. Although multiple component quantitations are now routinely being performed, NIRS is not an easy to use technique. Each specific application needs to be calibrated. The complex relation between chemical and physical structure of polymers can easily lead to misinterpretations by uncritical use. Clearly, NIRS is not a technique suitable for analysis of competitor products beyond the training set. 

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