Multi-spectral scanning

Many substances and materials have characteristic spectral signatures in that part of the IR region which is not covered by photographic emulsions. As a general-purpose technique in wide wavelength regions Multi-Spectral Scanning (MSS) performed from an aeroplane, or better still a satellite, can be used. The principle of this technique is illustrated in Fig.6.77. 

Multi-spectral imaging and linear unmixing add a whole new dimension to laser scanning fluorescence microscopy. Biotechniques 31, 1272-8. 

Figure 2. Grouping of proteins into color classes by multi-spectral image analysis. A liver extract was made in iso-urea sample buffer (20) and serial dilutions made from 1/16 to 1/1024. Gels were run on each sample dilution and the linear range was separately determined for blue, brown, red and yellow spots (see Figure 3). Spots from each color class were selected from the linear range and the intensity level from blue, green and red channels of a multispectral scan were used to calculate ratios as previously described...

Spectral interferences, such as line overlaps, are prevalent and must be corrected for accurate quantitative analysis. With a scanning instrument it may be possible to move to an interference free line. With a direct reader, sophisticated computer programs apply mathematical corrections based on factors previously determined on multi-element standards. 

Kumazaki, S., Hasegawa, M., Ghoneim, M., Shimizu, Y., Okamoto, K., Nishiyama, M., Oh-oka, H. and Terazima, M. (2007) A line-scanning semi-confocal multi-photon fluorescence microscope with a simultaneous broadband spectral acquisition and its application to the study of the thylakoid membrane of a cyanobacterium Anabaena PCC7120. J. Microsc., 228, 240-254. 

Complete MCP s can be stacked to provide even higher gains. For response in the vacuum ultra-violet spectral region (50-200 nm) a SSANACON, self-scanned anode array with microchannel plate electron multiplier, has been used (36). This involves photoelectron multiplication through two MOP S, collection of the electrons directly on aluminum anodes and readout with standard diode array circuitry. In cases where analyte concentrations are well above conventional detection limits, multi-element analysis with multi-channel detectors by atomic emission has been demonstrated to be quite feasible (37). Spectral source profiling has also been done with photodiode arrays (27.29.31). In molecular spectrometry, imaging type detectors have been used in spectrophotometry, spectrofluometry and chemiluminescence (23.24.26.33). These detectors are often employed to monitor the output from an HPLC or GC (13.38.39.40). 

VG Isotopes Ltd., is another leading manufacturer of ICP-MS equipment. The special features of their VG Plasmaquad PQ2 includes a multi-channel analyser which ensures rapid data acquisition over the whole mass range. The multi-channel analyser facilities include 4096 channels, 300 m facility for spectral analysis, user-definable number of measurements per peak in peak jumping mode, and the ability to monitor data as they are acquired. A multi-channel analyser is imperative for acquiring short-lived signals from accessories such as flow injection, electrothermal vaporisation, laser ablation, and so on, or for fast multi-element survey scans (typically 1 minute). 

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