UV-visible Spectroscopy for On-line Analysis

Marcel A. Liauw Lewis C. Baylor and Patrick E. O Rourke  

The use of ultraviolet (UV) spectroscopy for on-line analysis is a relatively recent development. Previously, on-line analysis in the UV-visible (UV-vis) region of the electromagnetic spectrum was limited to visible light applications such as color measurement, or chemical concentration measurements made with filter photometers. Three advances of the past two decades have propelled UV spectroscopy into the realm of on-line measurement and opened up a variety of new applications for both on-line UV and visible spectroscopy. These advances are high-quality UV-grade optical fiber, sensitive and affordable array detectors, and chemometrics. 

The emergence of sensitive and affordable array detectors in 1980s and 1990s has also improved measurement capability in the UV-vis. Commercially available UV-vis instrumentation with photodiode-array (PDA) detectors appeared in the mid-1980s. This made it possible to produce a UV-vis spectrophotometer 

Process Analytical Technology 2e Edited by Katherine Bakeev 2010 John Wiley Sons, Ltd. 

Process analyses On-line composition monitoring, closed-loop control Saltzman, 2000  

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Although product analysis seems essential for the clarification of complex ET processes involving biological molecules, only few attempts have so far been made. Ohde et al. [15,35] conducted bulk electrolysis to determine spectrophotometrically some redox products of interfacial ET reactions. Recently, Sawada et al. [39] have developed a microflow coulometric cell with a hydrophobic membrane-stabilized O/W interface. This microflow cell can accomplish complete electrolysis, and thus determination of the number of electrons for complex ET reactions at O/W interfaces. Also, its use for an on-line spectrophotometric detection of electrolysis products was made [43]. Figure 8.5 shows the spectmm change of the electrolyzed solution for the ET between Fc in NB and Fe(CN)e in W. When relatively small potentials were applied to the microflow cell, Fc" could be detected in the electrolyzed solution. The characteristic absorbance peak at 620 nm showed an undoubted existence of Fc+ in the W phase as the electrolysis product. This result would also support the IT mechanism. In situ UV-visible spectroscopy [44 46] also deserves attention for its usefulness in product analysis and clarification of reaction mechanisms. 

The spectroscopic techniques most commonly used for process analysis involve the use of infrared or UV/visible radiation. Mass spectroscopy has a considerable number of varied apphcations especially in the area of gas analysis. NMR technology is being increasingly used for a range of apphcations. Atomic spectroscopies, used extensively from a laboratory base for process control, are finding apphcations in automatic on-line measurement where the sampling systems can be suitably... 

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