Near-infrared analyzer

Light sources and detectors for near-infrared analyzers... 

Near-infrared Spectroscopy for Process Analytical Technology 127 5.3.4 Fourier transform near-infrared analyzers... 

Section 5.3 described a number of alternative design and implementation strategies for near-infrared analyzers, suitable for operation in a process analytical environment. However, none of these analyzers can operate without a robust, maintainable and repeatable sampling interface with the process sample under consideration. In addition to this question of the optical interface to the sample, there is a whole wider area of concern, which is how far the particular sample interface is representative of the sample in the process as a whole. This complex issue is not addressed here, and is dealt with separately in Chapter 3. 

Where is it possible or desirable to locate the near-infrared analyzer modnle What hazardous area certification requirements apply to both analyzer and sampling system ... 

Where physical stream switching is acceptable, this arrangement allows for multiple sampling fast loops to feed a single near-infrared analyzer, with stream switching controlled by the analyzer. The analyzer will most likely need to be hazardous area comphant, but may be either located in a dedicated analyzer shelter, or may be field-mounted. 

NIR Technology Austraha 34 Clements Avenue Bankstown NSW 2200 Australia TEL 4-61 (0) 2 9790 6450 FAX 4-61 (0)2 9790 1552 EmaU nirtech zipworld.com.au URL http //www.lineart.zip. com.au/homepage.htm Near-infrared analyzers (Herschel region)... 

J. K. Daun, K. M. Clear, P. C. WiUiams. Comparison of three whole seed near-infrared analyzers for measuring quality components of canola seed. J Am Oil Chem Soc 71 1063-1068, 1994. 

J. Rodgers, et al.. Process Monitoring of the Moistnre and Finish-on-Fiber of Textile Prodncts Using a Portable Near InfraRed Analyzer, Pittsburgh Conference 2002, New Orleans, LA, 2002. 

FIGURE 15.1 Instruments commonly used to determine physical and chemical properties of cereal grains, (a) Boerner divider, (b) Electronic grain moisture tester (photograph from Desna Controls and Weighing, Inc.), (c) Near-infrared analyzer or NIR A. 

Near-infrared analyzer A widely used nondestructive and analytical method of detecting moisture, protein, oil, and other chemicals associated with grains or milled fractions. It is based on the principle that different chanical compounds reflect at different wavelengths in the infrared band of the light spectrum. 

Sucrose quantitation has also been performed by colorimetric methods. However, in recent years, automated enzymatic analyzers and instmmental methods (eg, ion chromatography and hplc) have become increasingly popular, as they provide greater sensitivity and accuracy. Near infrared (nir) spectroscopy is currendy under evaluation as a tool for sucrose quantitation in sugar mills and food processing operations. 

Photometric Moisture Analysis TTis analyzer reqiiires a light source, a filter wheel rotated by a synchronous motor, a sample cell, a detector to measure the light transmitted, and associated electronics. Water has two absorption bands in the near infrared region at 1400 and 1900 nm. This analyzer can measure moisture in liquid or gaseous samples at levels from 5 ppm up to 100 percent, depending on other chemical species in the sample. Response time is less than 1 s, and samples can be run up to 300°C and 400 psig. 

When the operating conditions are uniform and steady (there are no fluctuations in flow rate or in concentration of CO in the gas stream), the continuous sampling method can be used. A sampling probe is placed in the stack at any location, preferably near the center. The sample is extracted at a constant sampling rate. As the gas stream passes through the sampling apparatus, any moisture or carbon dioxide in the sample gas stream is removed. The CO concentration is then measured by a nondispersive infrared analyzer, which gives direct readouts of CO concentrations. 

Finally, in the field of full-spectrum NIRS methods, Fourier transform near-infrared (FTIR) analyzers are included (Figure 5.5). FTIR techniques are predominant in mid-infrared spectroscopy because there are clear and absolute advantages for the FTIR analyzer in the mid-infrared compared with any other available technology. This arises because of the low power output of mid-infrared sources and the low specific detectivity... 

Simply stated, fiber-optic cable allows for the transfer of light from one point to another withont going in a straight line, and as such their use in process analytical apphcations is highly seductive. In a likely near-infrared process application there may be multiple sample stream take-offs, each with different sample characteristics, located in positions spread around a process unit, with the only apparently convenient analyzer location some distance away. 

O. Berntsson, L-G. Danielsson and S. Folestad, Estimation of effective sample size when analyzing powders with diffuse reflectance near-infrared spectrometry. Anal Chim. Acta, 364, 243-251 (1998). 

The objective of this chapter is to reduce the learning curve for the application of near-infrared (NIR) spectroscopy, or indeed any process analytical technology, to the chemical industry. It attempts to communicate realistic expectations for process analyzers in order to minimize both unrealistically positive expectations (e.g. NIR can do everything and predict the stock market ) and unrealistically negative expectations (e.g. NIR never works don t waste your money ). The themes of this chapter are value and... 

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