Monitoring, NIRS analyses

MONITORING NIRS ANALYSES 17.7.1 Standard Error of a Difference... 

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

A further example of process quality monitoring and reactor batch profiling using NIRS comes with oleo-chemical and biodiesel production. An established use of FT-NIR analysis (AOCS Method Cd le 01) is the determination of the key vegetable oil processing parameters - iodine value (IV) and percentage trans fat content (%Trans) (Figure 5.38). 

The NIR spectrometer used for method development and sample analysis was a Foss NIR Systems Model 6500 Forage Analyzer with a sample transport module and a standard reflectance detector array. The transport module moves the sample compartment up and down during data collection, thereby allowing a more representative spectrum to be obtained from bulky heterogeneous samples. The reflectance array uses two silicon detectors to monitor visible light from 400-850 nm and four lead-sulfide detectors to monitor NIR light from 850-2500 nm. Natural product sample compartment cells in 1/4-cup and 1-cup sizes were used as sample holders in the transport module. This instrument has a maximum resolution of 2 nm. 

Key words extrusion monitoring NIR polymer quantitative analysis... 

A particular attraction of NIR analysis is the possibility of using it online to monitor meat constituents continuously. Fiber optic probe technology has been successfully adapted to deliver the incident energy and record the reflected energy from the sample. A... 

A short note on reference analysis The very first step in application of NIRS to analysis of a commodity should be that of determination of the error of the reference methods used in development of calibration models. This is the starting point of any NIRS analysis. Calibration model development and ongoing monitoring of accuracy and precision of analysis will always have to rely on reference analysis for verification of results. One of the serendipitous results of NIRS application worldwide has been the discovery in many operations of the need for improvement in their own hitherto sacrosanct wet chemistry laboratory practices. 

NIR analysis of whole grain can also be accomplished on-line so as to monitor continuously the composition of the grist. An example of this type of equipment is the Infratec 1725 On Line Grain Analyzer. The optical component of the Infratec 1725 is identical to that of the laboratory Infratec 1225, and the same calibrations... 

B. Czarnik-Mamsewicz, K. Murayama, Y. Wu, Y. Ozaki. Protein-water interaction monitored by analysis of near infrared spectra. In Near Irfrared Spectroscopy. Proceedings of 11th International Conference, A. M. C. Davies, A. Garrido-Varo, eds. NIR Publications, Chichester, UK, 2004, p. 913-918. 

These tests should be made whenever there is some reason to believe that an equation may not be performing well. At a minimum, at least one sample out of every 100 should be set aside for reference method analysis after NIRS analysis. One in 50 would be better. When nine monitoring samples have been accumulated, they should be analyzed by the reference method and evaluated using the method described. 

Another example of the uniqueness of combination bands is the resolution of the O—H and N—H bands as seen when monitoring epoxide curing with NIR spectroscopy. The O—H and N—H fundamental bands often overlap in the mid-IR whereas they are distinguishable in the NIR region. Further discussion of NIR analysis of epoxy curing reactions is covered later in this chapter. 

Unlike a single wavelength UV monitor, or a refractive index monitor, a NIR analyser is not a single parameter measurement device. In a process situation, NIR analysis is carried out in a manner similar... 

Automatic polymer waste sorting plants based on NIR identification are operative (c/r. Chp. 1.2.2). For identification and sorting of carpets a portable NIR spectroscopic system - CarPID - was developed [139]. Other reported NIRS applications are to be found in the quantitative analysis of copolymers or blends the near-IR range allows for accurately monitoring of the monomer ratio and residual monomer content. Ikeda [140] used near-IR spec-trochemical analysis in controlled manufacture of polyester plasticisers. Jones et al. [141] similarly described the use of NIR analysis for controlling plasticiser ester formation the esterification of phthalic anhydride by isodecyl alcohol was exemplified. 

Several resin producers have considered programs for the introduction of on-line NIR analysis into their production facilities, i.e. process control of additive dosage. NIRS has been used to monitor polymer melts for polymer and/or additive composition with in situ analysis in transmission, trans-flectance and reflectance modes. Research on the application of NIRS to in-line and on-line additive analysis in melts (Table 7.21) is as yet by no means as extensive as in case of UV (Table 7.15) and mid-IR (Table 7.17). Batra etal. [143] have applied NIRS... 

The potential applications of NIR OFCD determination of metal ions are numerous. The detection of metal contaminants can be accomplished in real-time by using a portable fiber optical metal sensor (OFMD). Metal probe applications developed in the laboratory can be directly transferred to portable environmental applications with minimal effort. The response time of the NIR probe is comparable to its visible counterparts and is much faster than the traditional methods of metal analysis such as atomic absorption spectroscopy, polarography, and ion chromatography. With the use of OFMD results can be monitored on-site resulting in a significant reduction in labor cost and analysis time. 

IR is one of three forms of vibrational spectroscopy that is in conunon use for process analytical measurements the other two being near-lR (NIR) and Raman. Each one of these techniques has its pros and cons and the ultimate selection is based on a number of factors ranging from sample type, information required, cost and ease of implementation. The sample matrix is often a key deciding factor. NIR has been the method of choice for many years within the pharmaceutical industry, and sample handling has been the issue, especially where solid products are involved. IR is not particularly easy to implement for the continuous monitoring of solid substrates. However, often there is no one correct answer, but often when the full application is taken into account the selection becomes more obvious. In some cases very obvious, such as the selection of IR for trace gas analysis - neither NIR nor Raman is appropriate for such applications. 

Carl Zeiss, Inc. also describes a spectrofluorometer system for process monitoring," but it does not currently appear as a standard marketed product on their web site. HORIBA Jobin Yvon also markets a fluorescent process analyzer, but it is a laser-induced time-domain based measurement system tailored for uranium or equivalent analysis." Finally, while numerous miniature spectrofluorometers are also available (Carl Zeiss, StellarNet Inc., Ocean Optics and Avantes), they are not packaged and configured for process applications. Although there is an established need and continued growing interest in realtime process spectrofluorometry, relative to conventional process spectroscopic instruments such as NIR, UV-vis and Raman, commercial process spectrofluorometers are currently available on a very limited basis. 

In some manufacturing process analysis applications the analyte requires sample preparation (dilution, derivatization, etc.) to afford a suitable analytical method. Derivatization, emission enhancement, and other extrinsic fluorescent approaches described previously are examples of such methods. On-line methods, in particular those requiring chemical reaction, are often reserved for unique cases where other PAT techniques (e.g., UV-vis, NIR, etc.) are insufficient (e.g., very low concentrations) and real-time process control is imperative. That is, there are several complexities to address with these types of on-line solutions to realize a robust process analysis method such as post reaction cleanup, filtering of reaction byproducts, etc. Nevertheless, real-time sample preparation is achieved via an on-line sample conditioning system. These systems can also address harsh process stream conditions (flow, pressure, temperature, etc.) that are either not appropriate for the desired measurement accuracy or precision or the mechanical limitations of the inline insertion probe or flow cell. This section summarizes some of the common LIF monitoring applications across various sectors. 

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