In-situ electrochemical monitoring

In situ electrochemical monitoring of TNT using underwater vehicle platforms... 

J. Wang, J. Wang, J. Lu, B. Tian, D. MacDonald, K. Olsen, Flow probe for in situ electrochemical monitoring of trace chromium. Analyst 124 (1999) 349—352. 

Hu, R., Guille, M., Arbault, S., Lin, C. J., Amatore, C. 2010. In situ electrochemical monitoring of reactive oxygen and nitrogen species released by single MG63 osteosarcoma cell submitted to a mechanical stress. PCCP 12 10048-10054. 

Wang J (2000) In situ electrochemical monitoring from reanote sensors to submersible microlaboratories. Lab Robot Automat 12 178-182... 

In situ EPR spectroelectrochemistry monitors paramagnetic species, usually radicals in solution. The chemical stability of such species can be readily determined by this technique. It was seen that the most conunon problems encountered with in situ electrochemical EPR work emanate from the use of absorbing solvents and polymers containing paramagnetic impurities. 

Initial attempts to monitor the deposition reaction in real time using STM under in-situ electrochemical conditions gave inconsistent results. These were rationalized by assuming that the tunneling tip locally enhances the metal deposition reaction. This assumption is supported by the observation that after a long experiment, a brown spot of about 0.5-mm diameter was visible on the crystal surface at the location of the tip. Much work will be necessary before such an approach can become common practice. Thus, the deposition was performed in a conventional electrochemical cell, and the modified surface was subsequently imaged, after transfer to the STM cell. 

An alternative in situ electrochemical method provides another piece of valuable information. Resistometry, a technique invented by Fletcher and coworkers, and first used for CEPs in our laboratories,146 enables changes in the resistance of conducting polymers to be monitored in situ. The increase in resistance of the polymer material as it is reduced is obvious (Figure 1.23c). The definite potential/time lag between the current flow and resistance change is also apparent. This lag is due to the finite time required for the chemical processes causing the resistance change to occur. 

Kim H-O L, Tierney M J, Oh S and Madou M 1992 In-situ electrochemical sensor for oil quality monitoring Proc. Sensors Expo (Chicago, IL, 1992) (Peterborough, NH Helmers) pp 199-203 Janata J 1989 Principles of Chemical Sensors (New York Plenum) pp 112-6 Whiteley L D and Martin C R 1987 Perfluorosulfonate ionomer film coated electrodes as electrochemical sensors fundamental investigations Anal. Chem. 59 1746-51... 

An in situ electrochemical strain gauge method was applied to monitor the mechanical properties of conducting and redox polymers such as PP, poly(3,4-ethylenedioxypyrrole) and poly(3,6-bis(2-(3,4-ethylenedioxy)thienyl)-A-carbazole) during their redox transformations [282]. 

Electrochemical-SPR is also a powerful tool for monitoring the build-up of complex interfacial architecmres along with an in situ electrochemical characterization. For surface-attached biomembrane mimicks, SPR combined with electrochemical impedance spectroscopy is well established. ESPR has often been applied to study the formation and the properties of thin films and mono/multi-... 

Koca A (2011) Electrochemical and in situ spectroelectrochemical monitoring of the interaction between cobaltphthalocyanines and molecular oxygen in aprotic media. J Electroanal Chem 655(2) 128-139... 

Further sensor response modelling approaches are in development for other multi-gas sensor pairs. In summary, it is emphasized that accurate determination of plume gas ratios from co-deployed in situ electrochemical (and other) sensors requires a consideration of sensor response times. Non-identical sensor response times can result in scatter and bias in the derived gas ratios, particularly in cases where cross-sensitivities need to be removed. Reported plume gas ratios from multigas instruments may need to be revisited in this context, and the effect is likely also important in the monitoring of other environments, such as urban pollution. 

Miniaturisation of various devices and systems has become a popular trend in many areas of modern nanotechnology such as microelectronics, optics, etc. In particular, this is very important in creating chemical or electrochemical sensors where the amount of sample required for the analysis is a critical parameter and must be minimized. In this work we will focus on a micrometric channel flow system. We will call such miniaturised flow cells microfluidic systems , i.e. cells with one or more dimensions being of the order of a few microns. Such microfluidic channels have kinetic and analytical properties which can be finely tuned as a function of the hydrodynamic flow. However, presently, there is no simple and direct method to monitor the corresponding flows in. situ. 

Because silver, gold and copper electrodes are easily activated for SERS by roughening by use of reduction-oxidation cycles, SERS has been widely applied in electrochemistry to monitor the adsorption, orientation, and reactions of molecules at those electrodes in-situ. Special cells for SERS spectroelectrochemistry have been manufactured from chemically resistant materials and with a working electrode accessible to the laser radiation. The versatility of such a cell has been demonstrated in electrochemical reactions of corrosive, moisture-sensitive materials such as oxyhalide electrolytes [4.299]. 

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

Although limited by sensitivity, chemical reaction monitoring via less sensitive nuclei (such as 13C) has also been reported. In 1987 Albert et al. monitored the electrochemical reaction of 2,4,6-tri-t-butylphenol by continuous flow 13C NMR [4]. More recently, Hunger and Horvath studied the conversion of vapor propan-2-ol (13C labeled) on zeolites using 1H and 13C in situ magic angle spinning (MAS) NMR spectroscopy under continuous-flow conditions [15]. 

Unless the coverage of adsorbate is monitored simultaneously using spectroscopic methods with the electrochemical kinetics, the results will always be subject to uncertainties of interpretation. A second difficulty is that oxidation of methanol generates not just C02 but small quantities of other products. The measured current will show contributions from all these reactions but they are likely to go by different pathways and the primary interest is that pathway that leads only to C02. These difficulties were addressed in a recent paper by Christensen and co-workers (1993) who used in situ FT1R both to monitor CO coverage and simultaneously to measure the rate of C02 formation. Within the reflection mode of the IR technique used in this paper this is not a straightforward undertaking and the effects of diffusion had to be taken into account in order to help quantify the data obtained. 

Later, in Chapter 8 (Section 8.1.2), we will look at in situ spectroelec-trochemistry - the simultaneous monitoring of electrochemical processes with UV-visible spectroscopy. One of the best electrodes for this purpose is a thin film ofln(w) oxide doped with Sn(iv) oxide. Although this mixture of oxides has a relatively good electronic conductivity a, the magnitude of o is never high. 

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