Multi-stage techniques

Fig. 2.9. Comparison of analytical multi-stage techniques (left) and direct instrumental techniques (right)...

Despite the advantages of continuous cultures, the technique has found little application in the fermentation industry. A multi-stage system is the most common continuous fermentation and has been used in the fermentation of glutamic add. The start-up of a multi-stage continuous system proceeds as follows. Initially, batch fermentation is commenced in each vessel. Fresh medium is introduced in the first vessel, and the outflow from this proceeds into the next vessel. The overall flow rate is then adjusted so that the substrate is completely consumed in the last vessel, and the intended product accumulated. The concentration of cells, products and substrate will then reach a steady state. The optimum number of vessels and rate of medium input can be calculated from simple batch experiments. 

There are several techniques available for SFA to drive a sample along the normal direction and to position it to a specified site. A common feature of these techniques is to employ a multi-stage driving system of increasing sensitivity. The apparatus developed by Israelachivili s team, for example, uses a two-stage screw as the coarse and medium control, which gives positioning accuracy of 1 /rm and 1 nm. 

In some cases, sample preparation techniques are linked directly with analysing techniques using so-called multi-stage combined systems (Tolg [1979]) which frequently work in a closed system. The principle is shown in Fig. 2.9 in contrast to a direct analytical system. 

The extraction, in combination with fractional separation of extracts in a multi-stage separation system, results in high-quality volatile oils [42,44]. Recently, this fractional separation technique has been refined by Reverchon and co-workers for selective precipitation of cuticular waxes and volatile oils [43,56],... 

In summary, it is expected that, for allelopathy studies, the analytic power of multi-stage chromatography-mass spectrometry techniques will generate much useful qualitative and quantitative data, thereby helping to unravel some of the remaining mysteries of the allelopathy phenomenon. 

This technique (Fig. 3.8), which is examined in greater detail in connection with the upgrading of aromatic CB cuts, is based on the use of a pseudo-countercurrent between the liquid feedstock and the adsorbent bed. The displacement or the soiid is in fact simulated by means of a rotary valve with multiple inlets and outlets, which causes a gradual change ita the injection and collection points of the liquid streams in the molecular sieve placed in a multi-stage column. 

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