Flow-cell designs porous

Preparative separations in the grams per injection level are different. Separations are run isocratic in 1- to 3-in columns with large pore, fully porous packings (35-60jUm). An analytical, two-pump system can just barely reach the 20-mL/min flow rates needed to run a 1-in column. Special preparative HPLC systems deliver flow rates of 50-500 mL/min to handle the larger bore columns. A stream splitter is used to send part of the flow through a refractive index detector with a flow cell designed for concentrated solutions. 

Figure 3.8 Amperometric detectors (a) measure the current that flows between the working electrode, usually a glassy carbon electrode, and a reference electrode, at a fixed voltage, usually close to the discharge potential for the compound. Coulometric detectors (b) are less common and are designed with a porous carbon flow cell so that all the analyte reacts in the cell, the amount of current consumed during the process being proportional to the amount of the substance.

The way in which the active microzone is retained also depends on its relationship to the detector (Fig. 2.6) and the type of interaction with the analyte or its reaction product. If the microzone is an integral part of the probe, an additional support (usually a membrane) is often required, so contact with the sample is hindered to some extent. On the other hand, a microzone located in a flow-cell can be retained in various ways. Thus, if the microzone consists of a porous solid or particle, the flow-cell is simply packed with two filters in order to avoid washing out (e.g. see [21]). Too finely divided solids (viz. particle sizes below 30-40 pm) should be avoided as they require pressures above atmospheric level, which complicates system design and precludes use of microzones with a high specific surface. Placing a separation membrane in a flow-cell is... 

Low efficiency cell designs (b) thin-layer (c) wall-jet. (d) High-efficiency cell design with porous working electrode in tube. Arrows indicate liquid flow... 

Denaturation, proton structure and, 288 Detection systems, for biopolymert, 3-5 Detector cell design, firr LCEC design criteria, 122 pdarographic detectors, 127-130 porous dectrodes, 130-I3S thin-layer aihpciometric flow cells, 122-123... 

Figure 3.4 Simplified designs of chromatographic ED cells (a) Thin-layer cell (b) Wall jet cell (c) Tubular cell (d) Porous flow-through cell and (e) Single fibre electrode.

In this section, only thin-layer, wall-jet, and porous flow-through cell designs will be described. More detailed information about cell designs and their configurations can be... 

This DMFC provides a closed-system operation-. Fuel cell designers believe that the porous silicon electrodes can be easily assembled into cells and stacks with minimum separation. The CFfjOFI fuel and the oxidant react at the catalyst locations in the porous silicon structure to generate electrical energy. After completion of the electrochemical reaction, leftover or residual fuel can be removed from the cells using a continuous flow of liquid tlirough the electrodes. 

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