In process analyses

Once the sampling protocol has been decided, the next step is analysis of the sample(s). Of course, sampling and analysis may also be integrated. In the past 50 years, the type of assays that were done in-process exploited the nonselective properties of the process stream, such as density, viscosity and conductivity. This monitoring has been achieved by both automatic and automated instruments. Selective properties of the process stream, such as chemical composition, were usually measured by taking grab samples and examining them in a laboratory by off-line techniques as they are more difficult to adapt for process stream analysis. 

Automatic and automated instruments can be differentiated as follows automatic instruments tend to perform specific operations at given points in a process or analysis to save time or effort, e.g. robotics, while automated instruments tend to control some part of a process without human intervention and do this by means of a feedback mechanism from sensors. For example, an automatic conductivity detector might continuously monitor the conductivity of a process stream, generating some alarm if the conductivity goes outside a preset limit. An automated detection system could transmit the measured conductivity values to a control unit that, by utilising a feedback mechanism, adjusts relevant process parameters, e.g. temperature or cycle time, to maintain the conductivity of the stream within the preset limits. 

True process analytics are based on automated systems. Automated instruments must be smaller, more rapid and robust than laboratory instruments and designed for unattended operation. Those most commonly used are based on spectroscopic, separation and electrochemical analytical techniques. Many of these are incorporated into or combined with flow injection analysis (FIA) systems in order to work well. Not all analytical methods lend themselves to automation. Analyses involving gases and liquids are most successfully automated while those using solid samples are most difficult to automate. And there will always be certain assays that are too complex or too costly to automate. 

Continuous analysers make continuous measurements directly in the flowing process stream, in a bypass test stream or inside a reactor vessel. This works best when no pretreatment of the sample is required although simple manipulations, such as reagent addition, sample filtration or dilution, can be carried out prior to the analyser by a sample preparation chamber. Actual determinations are carried out in a flow-through sample cell. 

Continuous analysers are automated and operate on-line or in-line. They are usually incorporated into a control loop which operates by means of a feedback mechanism 

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Implement in-process analysis to determine if thermally unstable component is consumed or converted... 

J.M. Chalmers (ed.), Spectroscopy in Process Analysis , Sheffield Academic Press, Sheffield, 2000. 

MacGregor, J. F., Marlin, T. E., Kresta, J. V., and Skagerberg, B., Multivariate statistics methods in process analysis and control. In Chemical Process Control, CPCIV, (Y. Arkun and W.H. Ray, eds.). CACHE, AIChE Publishers, New York, 1991. 

In polymer/additive deformulation (of extracts, solutions and in-polymer), spectroscopic methods (nowadays mainly UV, IR and to a lesser extent NMR followed at a large distance by Raman) play an important role, and even more so in process analysis, where the time-consuming chromatographic techniques are less favoured. Some methods, as NMR and Raman spectrometry, were once relatively insensitive, but seem poised to become better performing. Quantitative polymer/additive analysis may benefit from more extensive use of 600-800 MHz 1-NMR equipped with a high-temperature accessory (soluble additives only). 

In the field of in-process analysis, analytical NMR applications also constitute a growth area - and also in relation to additives. This stems from the fact that the method makes it possible to use chemical analytical data in polymer quality control. Robust tools for hostile chemical plant environments are now available. The field of process analytical chemistry has been pushed to the forefront of the partnership between industry and academia. 

Both time- and position-dependent concentration functions can be dealt with by the theory of stochastic processes (Bohacek [1977]). Time functions playing a role in process analysis can be assessed not only by means of information amount M(n)t but also - sometimes in a more effective way -by means of the information flow, J, which is generally given by... 

In process analysis, the columns of A represent different measurement techniques (temperatures, pressures, etc.) and the rows represent the measurement output at different times. In that case... 

Hirschfeld T., Callis J.B., Kowalski B.R., Chemical sensing in process analysis, Science 1984 226 312. 

D.S. Goldman, Near-Infrared spectroscopy in process analysis, in Encyclopedia of Analytical Chemistry, J.W. Peterson (ed.), vol 9, Process Instrumental Methods, John Wiley Sons, New York, 2000. 

J.P. Coates, P.H. Shelley, Infrared Spectroscopy in Process Analysis, in Encyclopedia of Analytical Chemistry, Ed. R.A. Meyers. John Wiley Sons, Ltd., Chichester UK, pp. 8217-8240, 2000. 

H. Herman, Uv-Vis, fluorescence and chemiluminescence spectroscopies in chemical process analysis, in Spectroscopy in Process Analysis, J.M. Chalmers (Ed), CRC Press, Boca Raton, 1999. 

Spectroscopy in process analysis Edited by John M. Chalmers... 

Leonard, E. F., and Ruszkay, R. J., Frequency, transient and moment methods in process analysis. Paper presented at A.I.ChiE. Meeting, New York, December, 1961. (I)... 

Mass Spectrometers as Process Analyzers. The use of mass spectrometers in process analysis lias not been widespread because nl its perceived complexity and high cost. Technological advancements over the past decade or two have reduced costs and simplified mass spectrometry to the point where it is suitable lor a number of process analytical applications in place of infrared absorption or gas chromatography mass spectrometer is well accepted in such applications hecause of low cosi. good reliability, and ease of cnmpuicr-controllcd interfaces. 

Ammonia Gas Sensor. The determination of ammonia is important in process analysis. An ammonia gas electrode is usually used for this purpose. However, volatile compounds such as amines often interfere with the determination of ammonia. Therefore, a sensor based on amperometry is desirable for the determination of ammonia. 

Stark, E.W., Near-Infrared Array Spectrometers. In Chalmers, J.M. and Griffiths, P.R. (eds), Handbook of Vibrational Spectroscopy, vol 1 John Wiley 8c Sons New York, 2002, pp. 393-422. Goldman, D.S., Near-Infrared Spectroscopy in Process Analysis. In Meyers, R.A. (ed.), Encyclopedia of Analytical Chemistry, vol 9 Process Instrumental Methods John Wiley 8c Sons New York, 2000, pp. 8256-8263. 

Leugers, M.A. 8c Lipp, E.D. Raman Spectroscopy in Chemical Process Analysis. In Chalmers, J.M. (ed.) Spectroscopy in Process Analysis 1st Edition Sheffield Academic Press Sheffield, England, 2000 pp. 139-164. 

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