Open flow method

In the open-flow method (see Figure 5.15c), at each step a fresh solution of... 

In the circulation method, the same solution is continuously passed through the sample, also with continuous monitoring of the concentration, until equilibrium is reached (see Figure 5.15d) (Kurbanbekov et al., 1969 Ash et al., 1973). Although this method requires a less conventional set-up than the immersion or open-flow methods, it presents the following advantages ... 

The cation pool method and the cation flow method, which are based on low temperature electrochemical oxidation, have opened up a new chapter in the chemistry of organic cations, which have been considered to be difficult to manipulate in normal reaction media. The indirect cation pool method, which... 

In the original stirred-flow method (Denbigh, 1944), there were two or more openings for the flow of reactants and one opening for the flow of effluent. The effluent is a complex of reactants and products. With time, a steady state is established representing a balance between reactant additions in the influent and loss of reactant through reaction occurrence in the effluent. This steady state simplifies the mathematical treatment such that,... 

The adsorption apparatus, shown in Figure 1, uses a static volumetric method to measure pure gas adsorption, and an open-flow adsorption/desorption method for mixture... 

With [Co(phen)3] + as oxidant for PCu(I), rate constants determined by the stopped-flow method approach zero at low pH, consistent with zero reactivity of the trigonally coordinated Cu(I) form. However, with [FelCNlel as oxidant there is sometimes difficulty in fitting rate constants to the relevant [H ] dependence, which leaves open the question as to whether the rates actually become zero (57). Whereas [Co(phen)3l + is believed to react with PCu(I) at both the remote (acidic) and the adjacent (hydrophobic) patches, [FefCNleP reacts predominantly at the latter. The instability of PCu(I) in solution at pH < 4.5 makes it difficult to settle this issue conclusively. The range of studies has been extended using the pH-jump method in which protein, at high pH (with relatively small concentration of buffer), is stopped-flow mixed with the redox reagent at low pH (with excess buffer), and this approach has been used more extensively in recent studies. 

A unique feature of flow methods as contrasted with batch methods is that flow methods are inherently open systems. Solute is continually added to the system with flow methods, and reaction products are continually removed. This unique feature produces special attributes for the flow methods that solve some of the problems associated with batch systems, but also involve some limitations as well. Perhaps the chief advantage of flow methods is the continual removal of reaction products that in batch reactors are allowed to accumulate. Another unique attribute of flow method.s is that the solution/soil ratio is much narrower than that used in batch reactors. In the... 

In order to understand how H2O and CO2 are exchanged between leaf tissues and the air, measurement of the photosynthetic isotope fractionation by open flow gas analysis is conducted in a gas exchange chamber under controlled conditions of temperature, light intensity and humidity, and CF-IRMS and GC are employed. " When the same method is applied to ecosystem isotope fractionation in a field experiment, the variation in atmospheric CO2 concentrations and S values primarily reflect variations in net photosynthesis (daytime) and respiration. The S and CO2 data also reflect these processes, but with added complications because of oxygen isotope exchanges with soil and leaf water pools. 

Automatic continuous-flow methods Involving the continuous introduction of sample into the system are implemented by means of two different configurations (a) open, in which the flow is wasted after passing through the measuring cell, and (b) closed, in which the flowing solution is returned to the vessel to be recirculated once it has passed through the detector. 

Disulfides play a prominent role in pharmaceuticals, pesticides, and rubber vulcanization reagents. In biological systems, disulfide bonding is essential for peptides and proteins to fold into their active conformation. Noel et al. reported a mild batch and continuous-flow method to access disulfides by the aerobic oxidation of thiols [48]. Initially, an open flask batch procedure with Eosin Y (1 mol%) as catalyst resulted in near quantitative yields for a variety of thiophenols and heteroaromatic and aliphatic thiols, within 16 h. Moreover, it was found that the... 

FFF technology is applicable to the characterization and separation of particulate species and macromolecules. Separations in FFF take place in an open flow channel over which a field is applied perpendicular to the flow. Among the various FFF subtechniques, depending on the kind of the applied external fields, sedimentation FFF (SdFFF) is the most versatile and accurate, as it is based on simple physical phenomena that can be accurately described mathematically. SdFFF, which uses a centrifugal gravitational force field, is a flow-modified equilibrium sedimentation-separation method. Solute layers that are poorly resolved under static equilibiium sedimentation become well separated as they are eluted by the laminar flow profile in the SdFFF channel. In normal SdFFF, where the colloidal particles under study do not interact with the channel wall, the potential energy of a spherical particle, (p(x), is related to the particle radius, a, to the density... 

Enzymes have been successfully applied in the field of continuous-flow methods, especially in immobilized-enzyme reactors such as packed column and open tabular wall and single bead string reactors. All these systems have facilitated the development of FIA methods of great interest to biochemsitry and clinical and pharmaceutical chemistry, with the aid of various detectors, notably of the potentiometric, amperomet-ric, photometric, luminescence, radiometric and colorimetric types. 

The most widely used methods of chemical vapor deposition are chemical synthesis processes performed in open-flow systems. Here the constituents of the crystal to be grown are transported as volatile chemical compounds, mostly independent from each other in the case of a crystalline compound, into the deposition zone, where they decompose and/or react with each other. In most cases appropriate gaseous compounds are available that also exist at room temperature. Sometimes, however, appropriate feed gas compounds are stable only at high temperatures and must therefore be synthesized only within the reactor (GaCl(g) is a typical example). 

In these methods, a continuous supply of feed gases into the deposition zone can be provided. The feed gases can also be transported by means of an inert carrier gas, whose flow can be easily controlled. Thus, in open-flow systems, changes in the gas supply can easily be realized in any desired manner, and the sources are inexhaustive. 

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