On-line spectroscopy

Kinetic studies on SCF phases are mostly associated with carrying out experiments under unusual and extreme conditions of pressure and temperature. It is therefore desirable to have on-line techniques that can provide reliable quantitative analysis of the major reaction species throughout an experiment, rather than measure final concentration(s) after a preselected reaction time. Infrared (IR) and near-infrared (NIR) spectroscopy are perfectly suited for this purpose as almost all chemical substances have relatively narrow characteristic IR/NIR absorption bands. Fourier transform spectroscopy allows the simultaneous measurement of the IR and NIR spectral range within seconds. 

2 Kinetic CoefOdents from Laser-Assisted Techniques 

For homopolymerizations of methyl methacrylate and of styrene, benchmark value data sets have already been put forward [19,20] and critical data evaluation, by this working party, of kp data for other alkyl methacrylates, functional methacrylates, and alkyl acrylates is underway. Values of for the ethene high-pressure polymerization have not yet been derived from PLP-SEC 

Fitting the measured conversion versus time trace to eq (4.6-1) yields the parameters and itp/fc, for narrow conversion intervals, usually well 

In contrast to the PLP-SEC experiment, an SP-PLP measurement may be carried out at any time during the course of a polymerization and k lki may be 

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C.E. MiUer, Chemometrics for on-line spectroscopy applications - theory and practice, J. Chemom, 14, 513-528 (2000). 

Miller, C.E., Chemometrics for On-Line Spectroscopy Applications Theory and Practice ... 

Figure 1.22 Schematic of the sequential pulse injection system developed byde Bellefon, adapted for high-throughput screening using on-line spectroscopy.

A second area of on-line spectroscopy that has experienced breakthrough technology improvements is near-infrared. Three areas of instrumentation have seen this technology breakthrough (a) computer controlled scanning and detection capabilities, (b) development of fiber optic probes, and (c) implementation of chemometric techniques. As in the FT-IR instrumentation, near-IR has benefited immensely from computer control to either scan the entire spectrum or to monitor specific areas. Equally important from a process perspective is the ability to use optical fibers to transmit the near-IR light between the process and the instrument. This allows the instrument to be placed in an area that does not... 

Characterization. In many cases, ftir is a timely and cost-effective method to identify and quantify certain functionaHties in a resin molecule. Based on developed correlations, ftir is routinely used as an efficient method for the analysis of resin aromaticity, olefinic content, and other key functional properties. Near infrared spectroscopy is also quickly becoming a useful tool for on-line process and property control. 

It is becoming more and more desirable for the analytical chemist to move away from the laboratory and iato the field via ia-field instmments and remote, poiat of use, measurements. As a result, process analytical chemistry has undergone an offensive thmst ia regard to problem solviag capabihty (77—79). In situ analysis enables the study of key process parameters for the purpose of definition and subsequent optimization. On-line analysis capabihty has already been extended to gc, Ic, ms, and ftir techniques as well as to icp-emission spectroscopy, flow iajection analysis, and near iafrared spectrophotometry (80). 

In addition, new technology developments, such as on-line Raman spectroscopy, x-ray diffraction and gc/lc are under commercialization for the 1990s. 

Sohd-state multi-element detector arrays in the focal planes of simple grating monochromators can simultaneously monitor several absorption features. These devices were first used for uv—vis spectroscopy. Infrared coverage is limited (see Table 3), but research continues to extend the response to longer wavelengths. Less expensive nir array detectors have been appHed to on-line process instmmentation (125) (see Photodetectors). 

Hentschel, P. et ah. Structure elucidation of deoxylutein 11 isomers by on-line capillary high performance liquid chromatography- H nuclear magnetic resonance spectroscopy, J. Chromatogr. A, 1112, 285, 2006. 

From the results obtained with in situ reflectance spectroscopy and on-line analytical methods, investigators at Universite de Poitiers proposed a complete mechanism for the electrooxidation of methanol at a platinum electrode. The first step of the electrooxidation reaction is the dissociative adsorption of methanol, leading to several species according to the following equations ... 

ENA was recently used for remote on-line corrosion monitoring of carbon steel electrodes in a test loop of a surge water tank at a gas storage field. An experimental design and system for remote ENA and collection of electrochemical impedance spectroscopy (EIS) data (Fig. 13) have been presented elsewhere. In the gas storage field, noise measurements were compared with electrode weight loss measurements. Noise resistance (R ) was defined as... 

Pusecker K, J Schewitz, P Gfrorer, L-H Tseng, K Albert, E Bayer (1998) On-line coupling of capillary electrochromatography, capillary electrophoresis, and capillary HPLC with nuclear magnetic resonance spectroscopy. Anal Chem 70 3280-3285. 

Iwasita T, Vielstich W. 1986. On-line mass spectroscopy of volatile products during methanol oxidation at platinum in acid solutions. J Electroanal Chem 201 403-408. 

K. Albert 2002, On-line LC-NMR and Related Techniques, Wiley Sons, Chichester, 306 pp. Specialized, contains NMR spectroscopy but not imaging. 

M. Maiwald, H. H. Fischer, Y.-K. Kim, K. Albert, H. Hasse 2004, (Quantitative high-resolution on-line NMR spectroscopy in reaction process monitoring), /. Magn. Reson. 166, 135. 

A. M. Wolters, D. A. Jayawickrama, C. K. Larive, J. V. Sweedler 2002, (Insights into the cITP process using on-line NMR spectroscopy), Anal. Chem. 74(16), 4191. 

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