In-situ Method

Combined VIM and X-ray Diffraction [39]. The crystallographic phase of (solid) products generated immediately by VIM experiments can be studied when performing both experiments simultaneously. The reduction of PbO and Pb(OH)Cl served as an example of this combination, showing strong evidence for a topotactic electrochemical solid-state reaction. 

Combined VIM and EPR Spectroscopy [40]. This combination allows for the in situ detection of electrochemically generated radicals. Studying the solid compounds TCNQ (7,7,8,8-tetracyanoquinodimethane) and organometallic trans-Cr(CO)2(dpe)2 [dpe l,2-bis(diphenylphosphino)ethane], it was shown that the radicals generated by either electrochemical reduction (TCNQ) or oxidation [trans-Cr(CO)2(dpe)2] of these solids are also solids. Dissolution and thus distinctively different appearance of the corresponding EPR spectra could be forced by suitable tuning of the electrolyte solution composition. 

Combined VIM and Electrochemistry [40]. Rather unexpectedly, solid compounds immobilized to an electrode surface adhere very well to such surfaces even when rotating such an electrode at a speed of up to 10 min Reaction products, when soluble, can conveniently be detected with the help of a ring disk electrode. 

Combined VIM and Light Microscopy [41,42]. Oberservation of color changes of immobilized microparticles is greatly assisted by combination of VIM with light microscopy, as demonstrated with electrochromic octacyanomolybdates and -tungstates. By refining the instrumentation, diffuse reflection can be measured and thus quantified. 

Combined VIM and UV/Vis spectroscopy of indigo immobilized on an ITO electrode has been described [43]. 

2 In situ Methods An in situ method is one which provides the information of interest during the course of the analysis being carried out. In situ methods most commonly applied in SIMS for defining the depth scale during the course of depth profile analysis include  

Measurement of a substrate of a known thickness or containing some marker layer at some known depth 

The sputter rate is then derived for the matrix of interest by dividing the derived thickness (depth) by the time required to sputter down to the respective interface. The interface depth is usually taken as the position in which some secondary ion signal representative of layer either rises or drops by 50% in intensity. As matrix effects can modify secondary ion intensities over such regions, care must be taken in signal selection. 

If a single substrate type is of interest, sputter rates can be derived using some marker present at some known depth. A marker in this case would represent some additional element or molecule present at some suitably low concentration such that  

It is easily detectable under the conditions used in the SIMS depth profile, i.e. displays a suitably high yield (see Section 3.3.2) 

BzBr + S02 Bz-S(V + Br which is followed by a fast homogeneous reaction BzS02- + S02 — Bz-S02 + S02 

Monitoring the decay of the ESR signal due to S02 enabled a rate constant of 180dm3mol1s 1 to be determined. Unfortunately, doubts occur about the hydrodynamics of flow over the grid electrode and the imperfect agreement between theory and experimental results can be attributed to this. 

Dohrmann et al. [42—45] developed a cell which yielded kinetic informa-References pp. 349-352 

The in-situ techniques of Cauquis, Kastening, and Dohrmann described above, although showing advantages over ex-situ methods, did not contribute significant advances towards a kinetic analysis of electrode mechanisms. Improvements upon this are shown by cells developed by several groups of workers for in-situ electrochemical ESR and are described in the following section. 

This section deals with contemporary in-situ electrochemical ESR methodology and concentrates on the use of such techniques for the investigation of kinetics and their decay mechanism. 

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University of Arkansas and Louisiana State University. In-Situ Methods for the Control of Emissions from Surface Impoundments and Landfills. Draft Final Report. Prepared for U.S. Environmental Protection Agency. Contract No. CR810856. June 1985. pp. 95. 

The in situ method using rat living intestine was simple and qualitative. However, it was difficult to evaluate the weak interaction between polymers and cell membranes quantitatively. Therefore, the lipid bilayer of liposome was used as a model of cell membranes for the quantitative evaluation for the affinity of the hydrophobized polymers (15). 

Ferrite is introduced into the aqueous media by two techniques. With the in situ method, ferrite is formed within the actinide-containing solution by addition of Fe(II), Fe(III), and sodium hydroxide. With the preformed ferrite method, ferrite solids are prepared separately and added to the actinide solution. 

The in situ methods more commonly used to obtain the surface roughness R = SRa/S8ram (where and Sgeom are the working surface and the geometric area, respectively) of electrodes are10 24 63 73 74 218 (1)... 

The huge literature on the electronic conductivity of dry conducting polymer samples will not be considered here because it has limited relevance to their electrochemistry. On the other hand, in situ methods, in which the polymer is immersed in an electrolyte solution under potential control, provide valuable insights into electron transport during electrochemical processes. It should be noted that in situ and dry conductivities of conducting polymers are not directly comparable, since concentration polarization can reduce the conductivity of electrolyte-wetted films considerably.139 Thus in situ conductivities reported for polypyrrole,140,141 poly thiophene,37 and poly aniline37 are orders of magnitude lower than dry conductivities.15... 

Mazurek M, Benker N, Roth C, Buhrmester T, Fuess H. 2006. Electrochemical impedance and X-ray absorption spectroscopy (EXAFS) as in situ methods to study PEMFC anode. Fuel Cells 6 16-20. 

The reaction can be carried out efficiently using aryl diazonium tetrafluoroborates with crown ethers, polyethers, or phase transfer catalysts.103 In solvents that can act as halogen atom donors, the radicals react to give aryl halides. Bromotrichloromethane gives aryl bromides, whereas methyl iodide and diiodomethane give iodides.104 The diazonium ions can also be generated by in situ methods. Under these conditions bromoform and bromotrichloromethane have been used as bromine donors and carbon tetrachloride is the best chlorine donor.105 This method was used successfully for a challenging chlorodeamination in the vancomycin system. 

J. M. Thomas, The ineluctable need for in situ methods of characterising solid catalysts as a prerequisite to engineering active sites, Chem. Fur. J., 1997, 3, 1557. 

The presence of an active site in the modifier is essential for the formation of polymer-modifier adduct by the in-situ method (method 2) above. Figure 3 compares the degree of binding which can be achieved... 

In Situ Methods for the Biological Treatment of Organic Contaminants. 539... 

A permeable reactive barrier (PRB) is defined as an in situ method for remediating contaminated groundwater that combines a passive chemical or biological treatment zone with subsurface fluid flow management. Treatment media may include zero-valent iron, chelators, sorbents, and microbes to address a wide variety of groundwater contaminants, such as chlorinated solvents, other organics,... 

In situ methods have potential use as an interim or emergency measure until dredging can be undertaken or as a primary remedial action where it is determined to be more cost-effective than removal. The biggest advantages are that they are much less costly than dredging, eliminate the need for dredged material management, and minimize the resuspension of contained sediments.15... 

Before the widespread adoption of FRET imaging techniques, the only optical, in situ method of assessing whether two proteins were... 

If we were to choose the ideal method for the analysis of any component of seawater, it would naturally be an in situ method. Where such a method is possible, the problems of sampling and sample handling are eliminated and in many cases we can obtain continuous profiles rather than limited number of discrete samples. In the absence of an in situ method, the next most acceptable alternative is analysis on board ship. A real-time analysis not only permits us to choose our next sampling station on the basis of the results of the last station, it also avoids the problem of the storage of samples until the return to a shore laboratory. 

Reactivity patterns of this in situ method also support the hypothesis that Pd oxidation occurs via the acidic phosphonium. This initial reaction would involve initial formation of a palladium hydride. Such hydride intermediates are usually very reactive due to the weakness of the Pd-H bond, which in turn imparts instability. 

The in situ method also appears to result in incomplete and inefficient use of palladium. As noted above, the ligand contains an acidic phosphonium hydrogen and can therefore also react with the initially formed Pd-H species to form a bischelated complex (two ligands per metal) as shown in Scheme 4. This bische-lated palladium is inactive for polymerization. Indeed the formation of these... 

A large variety of tools, utilizing both chemical and physical methods, are available to the experimentalist for rate measurements. Some can be classified as ex-situ techniques, requiring the removal and analysis of an aliquot of the reacting mixture. Other, in-situ, methods rely on instantaneous measurements of the state of the reacting system without disturbance by sample collection. 

Methods that investigate the interface as such are called in situ methods. In ex situ methods the electrode is pulled out of the solution, transferred to a vacuum chamber, and studied with surface science techniques, in the hope that the structure under investigation, such as an adsorbate layer, has remained intact. Ex situ methods should only be trusted if there is independent evidence that the transfer into the vacuum has not changed the electrode surface. They belong to the realm of surface science, and will not be considered here. 

In recent years, increasing use has been made of in situ methods in EM—as is true of other techniques of catalyst characterization such as IR, Raman, and NMR spectroscopy, or X-ray diffraction. Although the low mean-free path of electrons prevents EM from being used when model catalysts are exposed to pressures comparable to those prevailing in industrial processes, Gai and Boyes (4) reported early investigations of in situ EM with atomic resolution under controlled reaction conditions to probe the dynamics of catalytic reactions. Direct in situ investigation permits extrapolation to conditions under which practical catalysts operate, as described in Section VIII. 

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