Reagent nesting

Isolation of Citronellal and Citral. At the close of each experiment (7 to 10 days), the nests were frozen intact. Groups of 200 workers were placed in a micro-Soxhlet apparatus and extracted for 8 hours with methylene chloride. A few milligrams of carrier citronellal and citral were added and the mixture was applied to a thin-layer chromatoplate (silica gel G) which was developed with hexane-ethyl acetate (92 to 8) to separate citronellal and citral (3). The aldehydes were detected by spraying with a solution of 2, 4-dini-trophenylhydrazine in tetrahydrofuran (20) and the citronellal and citral peaks were scraped off and allowed to react with excess dinitro-phenylhydrazine reagent for a further 12 hours. 

Svoboda- Liver from TRIzol reagent HCV using nested RT-PCR is a... 

In the procedure described in this manuscript, the nested set of peptides was generated simply by adding fresh peptide to each cycle and driving both the coupling and cleavage chemistry to completion. No additional reagents were required to act as chain terminators. The process is summarised in Figure 1 and as follows ... 

Kemp and co-workers (K6) developed a colorimetric detection system that incorporates biotin into one (nested) primer and the sequence for a DNA-binding protein (e.g., the GCN4 gene from Saccharomyces cerevisiae) into the other primer. Amplified DNA is captured on an immobilized affinity reagent and the biotinylated product is detected with avidin-horseradish peroxidase and a chro-mogenic substrate. 

In order to accomplish nested introduction, two loop-based rotary valves with coincident movements [64] or a two-section injector—commutator have been used (Fig. 6.13). In the load position, specified in the figure, the first and second loops are simultaneously filled with the sample and with the reagent (or air, if a mono-segmented flow analyser is used). Switching the injector inserts the selected sample volume between two reagent (or air) plugs into the carrier/wash stream, and the complex zone established is directed towards the detector. 

FIGURE 6.13 Schematic representation of nested injection. The Figure refers to the load position. S = sample L = sampling loop R = reagent (or air) C = carrier/wash stream W = waste V = reagent recovery vessel M = towards manifold IC = injector-commutater shaded area = alternative position of the central sliding bar. For details, see text. 

The reaction of 44 with trihalides of Group 14 (Cl.iMR M - Si. Gc, Sn) or 15 (M - p. As. Sb) may lie performed in a one sicp 134a] or in i (wo-slop procedure 33a.34b.c,35] as shown in Scheme II.IS. Probably in both inodes of nddiliou. and favoured by the close vicinity of die lour magnesiums in the iclramcric cluster of 44, the reaction proceeds first by substitution of all three chlorines of one molar equivalent of Cl.iMR to furnish an intermediate tri-Grignard reagent 55 (which will be briefly discussed in Section I 1.6) nest. 54 is formed by reaction of 55 with the second equivalent of the trihalide. The two-step process is attractive because it allows... 

In the volumetric sample injection (Fig. 5.10a) the sample loop has its simplest function, that is, merely to meter the volume of the analyte to be injected. The next step is to inject the reagent and analyte simultaneously with the purposes discussed previously in Chapters 2 and 4. This can be done in two ways (1) by nesting another loop by means of a second valve in the way shown in Fig. 5.10/ , or (2) by splitting the sample loop as shown in Fig. 5.10c. 

Fig. 6 FI manifold with gas-diffusion separator nested in sample loop of the injection valve used for preconcentration of volatile species by time-bas sampling (sample loading sequence). AS, autosampler, T, heating thermostat (optional) CDS, gas-diffusion separator, V, injection valve Ri, reagent for generation of volatile species R2. acceptor reagent stream R3. derivatization reagent (optional) D, detector W, waste a, valve position in sample injection sequence. Crossed circles in valve represent blocked channels [20].

Fig.6J Schematic diagram of a FI dialysis system with sample circulation (valve in loading position). PI. P2 pumps DS, membrane dialyzer nested in sample loop A, acceptor stream R, reagent D, detector W, waste 111].

A reactive bed can be prepared using insoluble materials, provided they have the required mechanical and chemical resistance a more frequent procedure is to anchor the reagent to a solid support. The reactor can be nested at different points along an FIA manifold, depending on the purpose they serve. Some examples below are illustrative of some of the operational modes used in this context. 

In this chapter we introduced the basic physical chemistry that governs catalytic reactivity. The catalytic reaction is a cycle comprised of elementary steps including adsorption, surface reaction, desorption, and diffusion. For optimum catalytic performance, the activation of the reactant and the evolution of the product must be in direct balance. This is the heart of the Sabatier principle. Practical biological, as well as chemical, catalytic systems are often much more complex since one of the key intermediates can actually be a catalytic reagent which is generated within the reaction system. The overall catalytic system can then be thought of as nested catalytic reaction cycles. Bifunctional or multifunctional catalysts realize this by combining several catalytic reaction centers into one catalyst. Optimal catalytic performance then requires that the rates of reaction at different reaction centers be carefully tuned. 

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