Raman analysis remote spectroscopy

Raman spectroscopy, while typically used as a micro-analytical tool, can be conducted remotely. Performance of remote Raman analysis have been recently explored and reahzed for experiments on the surface of Mars (Sharma et al. 2001 Sharma et al. 2003). Raman spectroscopy is a powerful technique for mineralogical analysis, where the sharpness of spectral features of minerals allows for much less ambiguous detection, especially in the presence of mixtures. Visible, near-infrared, thermal, reflectance and in many cases emission spectroscopy of minerals all suffer from broad overlapping spectral features, which complicates interpretation of their spectra. On the other hand, Raman spectra of minerals exhibit sharp and largely non-overlapping features that are much more easily identified and assigned to various mineral species. 

For a review on the process control applications of Raman spectroscopy in the petroleum industry, see Ref. 8. For a remote fiberoptics study of Raman analysis of xylene, see Ref. 9. It appears that Raman spectroscopy can play an increased role in the petroleum field now that fluorescence is minimized. 

Abstract Thin and flexible probes made with hollow-optical fibers may be useful for remote spectroscopy. Experimental results showed that these probes are useful for endoscopic measurements of infrared and Raman spectroscopy. A hollow-fiber probe has been used for remote FT-IR spectroscopy in the form of endoscopic measurement of infrared reflectometry spectra inside the body. This measurement was made possible by the hollow-fiber probe s flexibility, durability, nontoxicity, and low transmission loss. A hoUow-fiber probe with a ball lens at the end works as a confocal system for Raman spectroscopy. It can thus detect the molecular structure of biotissues with a high signal-to-noise ratio. Owing to their small diameter, the probes are useful for in vivo, noninvasive analysis using a flexible endoscope. 

Quantitative and qualitative analyses of inorganic and organic compounds can be performed by Raman spectroscopy. Raman spectroscopy is used for bulk material characterization, online process analysis, remote sensing, microscopic analysis, and chemical... 

The last 4 years have seen a tremendous increase in the use of Raman spectroscopy in general and there is nowhere where this is more noticeable than in the area of process analysis. In comparison to the other optical spectroscopic techniques available, Raman spectroscopy offers a unique combination of well-resolved features and the ability to perform the analysis remotely by interfacing the spectrometer to the sample via standard silica fiber optics. Adar et al. [1] and Lipp and Leugers [2] have both reviewed the development of Raman spectroscopy for process applications in terms of necessary instrumentation and illustrated this with a discussion of several successful applications. Developments in fiber-optic probe design for Raman spectroscopy, up to mid-1996, have been thoroughly reviewed by Lewis and Griffiths [3] and more recently by Lewis and Lewis [4]. 

The future of Raman microspectroscopy is probably imaging and optical near-field nano-Raman spectroscopy [529], cfr. Chp. 5.5.2. While conventional laser Raman spectroscopy samples 10 g (mm ), /zRS handles 10 g (nm ) and near-field Raman spectroscopy 10 g (nm ). Mobile Raman microscopy (MRM) allows in situ Raman analysis [530]. One can expect further developments in the field of NIR multichannel Raman spectroscopy with the advent of 2D array detectors offering extended response in the NIR. With these 2D sensors it wiU become possible to apply in the NIR region the powerful techniques already developed in the visible, such as confocal line imaging techniques or multisite remote analysis with optical fibres. 

T. Hirschfeld and co-workers, "Remote Spectroscopic Analysis of Parts-Per-MiUion-Level Air Pollutants by Raman Spectroscopy," Appl Phys. Eett. 22(1), (fan. 1973). 

NIR, Raman would be expected to offer advantages such as ease of use for quantitative analysis. The reason for less widespread use of process Raman spectroscopy is due in part to more expensive equipment, relative to NIR. A broader implementation of process Raman spectroscopy in the pharmaceutical industry has previously also been hampered by inherent weaknesses in sampling in remote measurements on solids. This is discussed further in Section 10.3. 

Bowen, J.M. Sullivan, P.J. Blanche, M.S. Essington, M. Noe, L.J. Optical-Fiber Raman Spectroscopy Used for Remote In-Situ Environmental Analysis US 4,802,761 Assigned to Western Research Institute Filed in 1987. 

Distillation column monitoring was one of the first reports of using on-line Raman spectroscopy in real time for process analysis. This application used FT Raman coupled to a remote sample cell with optical fibers [27] to determine the bottoms product of a solvent recovery column. The system was linked to a control... 

The production of phosphorus trichloride from phosphorus and chlorine is an important step in the manufacture of a number of agrochemical products. Raman spectroscopy has been used to monitor the reaction and control the raw material feed rates. This maximises production of phosphoras trichloride, minimizes the formation of phosphorus pentachloride and ensures safe operation when plant shut-down periods are needed. Remote analysis is achieved using optical fibers to provide a safer operation and a more rapid analysis than was previously possible [29, 30]. 

HW Schrotter. Raman and infrared spectroscopic techniques for remote analysis of the atmosphere. In RJH Clark, RE Hester, eds. Advances in Infrared and Raman Spectroscopy, Vol. 8. London Heyden, 1981, pp 1-51. 

Another application of Raman spectroscopy to semiconductor production has been demonstrated by Pelletier et al. [159,160] in conjunction with Sematech (Austin, TX). Pelletier et al. [159] noted that as semiconductor devices and manufacturing become more complex, more stringent control of each step becomes important. One area identified, which may be monitored and thus controlled, by Raman spectroscopy is the concentration of components in chemical cleaning baths. In this application, the advantages of remote noncontact analysis are stabilized. These advantages are important because these chemicals are normally treated in a clean-room environment thus, the concern over bath product contamination is real. Other methods, including electrochemical, UV absorption, and NIR, have been applied to this application, but problems of possible contamination (electrochemical) or nonselectivity UV and IR have precluded their general adoption. 

NJ Everall, H Owen, J Slater. Application of an integrated Raman system for remote process analysis using a fiber optic probe, holographic spectrograph, holographic notch filter and CCD detector. In N-T Yu, X-Y Li, eds. Proceedings of the XIVth International Conference on Raman Spectroscopy. Chichester Wiley, 1994, pp 1110-1111. 

Principles and Characteristics As already indicated in Chp. 1.2.3, Raman scattering induced by radiation (UV/VIS/NIR lasers) in gas, liquid or solid samples contains information about molecular vibrations. Raman specfioscopy (RS) was restricted for a long time primarily to academic research and was a technique rarely used outside the research laboratory. Within an industrial spectroscopy laboratory, two of the more significant advances in recent years have been the allying of FT-Raman and FTIR capabilities, coupled with the availability of multivariate data analysis software. Raman process control (in-line, on-line, in situ, onsite) is now taking off with various robust commercial instrumental systems equipped with stable laser sources, stable and sensitive CCD detectors, inexpensive fibre optics, etc. With easy interfacing with process streams and easy multiplexing with normal (remote) spectrometers the technique is expected to have impact on product and process quality. 

Raman spectroscopy is complementary to IR and due to differences in the nature of the selection rules yields vibrational information not obtainable from IR. In many cases, Raman spectroscopy is particularly useful when ease of sampling and remote sampling is important. Raman also is advantageous in aqueous solution due to low Raman scattering of water. On the other hand, Raman has been utilized more as a research tool than an analytical tool for polymers. The basic reason for this practical limitation is the ubiquitous fluorescence which occurs with polymers. However, in recent years, tremendous progress has been made and Raman is becoming a more common tool for polymer analysis. 

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