Stopped-flow system for

Figure 3.7. Commercial stopped-flow system for fast liquid-phase reactions (courtesy KinTek Corporation, reproduced with permission).

Messina, G. A., A. A. J. Torriero, I. E. De Vito, and J. Raba. 2004. Continuous-flow/ stopped-flow system for determination of ascorbic acid using an enzymatic rotating bioreactor. Talanta 64 1009-1017. 

Commercially available CD spectropolarimeters, either stand-alone or with specific accessories, are capable of recording isotropic absorption and luminescence, ORD, LD, FDCD and MCD spectra. Moreover, they can also be equipped with thermostatic modules, flow cells, automatic titration devices, and stopped flow systems for the measurement of reaction kinetics. CD instmments are also employed as detectors in HPLC chromatography with chiral stationary phases. 

Depending on the configuration of the device and the method for sample and reagents introduction, it is possible to classify the systems into static (batch or discrete sampling instrument) or flowing stream, both using continuous-flow or stopped-flow systems. 

The possibility for automation is offered by the Voyager SF with its stop flow system, able to process larger reaction volumes by sequen-... 

Figure 2.15 — Variants of coupled continuous configurations and sensors accommodating an immobilized catalyst (Cat). (A) Conventional system. (B) Stopped-flow system. (C) Configuration with iterative reversal of the flow direction. (D) Open-closed circuit configuration. Symbol meanings are given in Fig. 2.14. For details, see text.

B. Serra, A.J. Reviejo, C. Parrado and J.M. Pingarron, Graphite-Teflon composite bienzyme electrodes for the determination of L-lactate application to food samples, Biosens. Bioelectron., 14(5) (1999) 505-513. A.A.J. Torriero, E. Salinas, F. Battaglini and J. Raba, Milk lactate determination with a rotating bioreactor based on an electron transfer mediated by osmium complexes incorporating a continuous-flow/ stopped-flow system, Anal. Chim. Acta, 498(1-2) (2003) 155-163. 

Aliquat 336 TEVA-Resin "Tc determination in SI system using stopped-flow detection for nuclear waste On-line liquid scintillation 44... 

Morrall2 used a HPLC system with two columns. The first column was loaded with the controlled pore glass (CPG) to be modified. The second column was used for separation of the reaction effluents. This column was coupled to a refractive index detector, allowing for quantitative detection of the effluents. The reaction was initiated by injecting an APTS/toluene mixture and stopped by injection of pure toluene. With this so-called stop-flow mechanism reaction times down to 18 seconds could be used. From these analyses it became evident that upon mixing of the aminosilane with the silica, a very rapid physisorption occurs. The initial adsorption of the APTS (from toluene solution on dried CPG) occurred before the 18 second minimum time delay of the stop-flow apparatus. For non-aminated silanes the adsorption proved to be much slower. This study also revealed the pivotal role of surface water in the modification of siliceous surfaces with alkoxysilanes, as discussed in the previous chapter. 

Inherently, the FI A stopped-flow procedure should be an ideal vehicle to determine reaction rates and rate laws, provided that an experimental approach could be designed that allows resolving the individual contributions of physical dispersion and chemical kinetics. A comprehensive treatment of this problem was recently described by Hungerford et al. [838], who pointed out that although the single-line stopped-flow system (Fig. 4.15a cf. Fig. 4.11) allows optimization of solution conditions for measurement during a selected stopped-flow time interval (fs) by choosing... 

When we examine the time distribution of the recorded signal (Fig. 4.18c), it is apparent that the peak width at its base in this system is approximately twice as long as the time interval between the sample injection and the moment when the signal starts to rise. In a simple stopped-flow system this time distribution does not present a problem because a new cycle is initiated only when the next sample is injected. The timer for a two-channel parallel stop analysis must, however, run in a fixed go-stop-go cycle, because while one sample zone is being injected (or flushed out) the other is stored, and if the length of the storage period is not always the same, the analyzer will not yield reproducible results-unless, of... 

Following basically Robinson et al. [159] who used a stopped flow method for kinetic studies of the reaction between hydrated nickel (II) and murexide in the system AOT-water-heptane, one can visualize the following steps ... 

The stopped-flow technique was introduced by Chance in 1940. Earlier applications to kinetic analysis were concerned with studies on kinetics and reaction mechanisms (e.g., the formation of the iron(ni)-thiocyanate complex, that of 12-molybdo-phosphoric acid, the redox reaction between 2,6-di-chlorophenolindophenol and ascorbic acid, etc.) as well as the resolution of mixtures of metal ions using substitution reactions. On the other hand, the inception of commercially available stopped-flow instruments and inexpensive modular mixing systems for adaptation to existing detectors have led to a broad use of this technique in routine kinetic determination of individual species and mixtures in a variety of samples of clinical, pharmaceutical, nutritional, and environmental interest. The analytical features of the methods developed for this purpose usually surpass those of the equilibrium counterparts, as shown by the selected examples given in Table 2. In addition, stopped-flow systems accelerate some slow reactions relative to the conventional kinetic technique as a... 

A typical stopped-flow system is assembled from modular components of a conventional spectrophotometer/fluorimeter, a device permitting rapid mixing of the components of a reaction and a data recording system with a fest response. Commercially available instruments offer facilities for the observation of changes in absorption and/or fluorescence emission after rapid mixing of the... 

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