Basic manifold Configurations

The basic configuration of a FI manifold for on-line dialysis with volume-based sampling is shown in Fig. 6.1. The manifold differs from gas-diffiision manifolds in that usually no reagents are added to the donor stream while most applications involve merging of a reagent to the acceptor stream to transform the dialysate into a detectable species. 

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The basic FI manifold configuration for hydride generation atomic spectrometry has varied little since the early publications, and a typical manifold using the gas-expansion separator in Fig. 5.4 b is shown in Fig. 5.9. The injected samples are usually preacidified to contain IM HCI and transponed by an IM HCl carrier stream to merge with the borohydride reductant flow at a confluence point. The reaction mixture passes through a length of reaction coil and merges with an inert carrier gas flow which carries the liquid-gas mixture into the gas expansion separator. The separation of the gas from the reaction mixture is achieved as described in Sec. 5.2.4. and the hydride is transported into the heated T-shaped quartz atomizer for atomization. 

Process Configuration Figure 22-56 shows a basic cell pair. A stack is an assembly of many cell pairs, electrodes, gaskets, ana manifolds needed to supply them. An exploded schematic of a portion of a sheet-flow stack is shown in Fig. 22-60. 

The basic components of the system are a liquid driver with only one carrier stream, a multi-port selection valve and a detector (Fig. 2.9). The valve is the heart of the sequential injection system and normally comprises 6—10 peripheral ports and a central port in a multi-position valve configuration. The central port is linked to a holding coil and the peripheral ports are connected to different solution aspiration tubes and transmission lines that are linked to different manifold components, e.g., detector and mixing chamber. Only one peripheral port is connected to the central port at any one time. Stream management inside the holding coil is accomplished by a bi-directional piston (or peristaltic) pump. The analyser is fully computer controlled and the injection volumes, residence times, delivery of solutions and analytical path lengths are selected based on a valve timing sequence and related flow rates. 

An example of the use of an intermolecular carbopalladation in complex molecule synthesis is the preparation of a PAF (platelet activating factor) antagonist (Scheme 11). In the key step, an intermolecular Heck reaction of 2-naphthyl triflate with 2,3-dihydrofuran 71 yields 2-naphthyl-2,3-dihydrofuran 72 in 52% yield with excellent enantioselectivity. The reaction presumably occurs via the cationic manifold and the alkene is isomerized by a hy-dropalladation/dehydropalladation reaction. The minor product 2,5-dihydrofuran 73 is obtained in 26% yield with modest enantioselectivity favoring the opposite absolute configuration at the key center. Critical to the reaction is the use of the sterically demanding and highly basic proton sponge [l,8-bis(dimethylamino)naphthalene] as the base. It is... 

The basic coextrusion process consists of the generation of two or more melt streams and their confluence while in the melt phase. The number of separate extrusion systems is determined by the number of polymer types. This is typically 2, but occasionally 3 and exceptionally up to 10. Each polymer type to be incorporated in the structure is separately melted, pressimized, and (optionally) filtered in parallel extrusion systems before flowing into the coextrusion hardware. The optimum method of bringing the separate melts together depends primarily on their respective flow behaviors. The melt layers must remain distinct but well bonded in the process from the point(s) of confluence through to sohdification. There are basically two hardware configurations in use for common polymers the multi-manifold die and the injector block. Combinations of the two are also possible for complex structures (8,9). 

Depending on the objective and the application, the DUs can be implemented in different positions of flow manifold, which defines the mode of selecting the sample volume. Figure 12.4 shows possible configurations of a DU inserted in a basic flow injection... 

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