Flow Exit Modes

10 Schematic presentation of the flow exit modes of FI liquid-liquid extniaion systems. 

For details, see text. SR phase separator, R, restrictor or impedance coil D, detector  

The separated extracts containing the analyte are presented to the detector through different modes of delivery, depending on specific features of the detection systems. The modes may be categorized as  

The different modes are shown schematically in Fig. 3.11 a, b. c, respectively, with an impedance coil as the exit mode. Mode a, which is characterized by continuous deliver of the separated phase to the detector immediately following separation, is used mainly for spectrophotometric, fluorimetric and chemiluminescence detectors, although it is also occasionally used with atomic spectrometric detectors when optimum sensitivities are not required. 

Mode b is used mainly for flame AA and ICP spectrometric systems, which require specific sample uptake rates for achieving optimum sensitivities. The exit flow-rates of the separated phase are normalh too low to meet the demands of the detector, particularly when large phase ratios are used to achieve high EF values. For this reason a supplementary interface, composed of an additional sampling valve, is used to collect a defined volume of the separated phase (concentrate) under the low flow-rates optimized for the extraction and separation. The collected concentrate is then injected into a carrier and delivered to the detector at the required flow-rates for obtaining optimum detection signals. 

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To establish the validity of the numerical scalar technique for RTD analysis, the normalized exit age distribution curve of both counter-current (Figure 1 (a-b)) and cocurrent (Figure 1 (c-d)) flow modes were compared. Table 1 shows that a good agreement was obtained between CFD simulation and experimental data. 

Imagine photons to be streaming from the entrance slit of area A toward the exit slit. These of course include all wavelengths of the source. Picture next just photons of one wavelength (or wave number) xm as they flow from the entrance slit. Because these are quantum-mechanical entities, they cannot occupy continuously all positions in space during their flow. Instead, they may occupy only finite positions in space, called degrees of freedom (df) or modes. These are shown schematically as cubes in Fig. 3. Note that there are but a finite number zm of such cubes and that we must subscript z because the number of modes will vary from one wavelength to another. 

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