Tubular formations

The tube structure consists ofsmall tubular formations to represent so-called coils and turns (sec the tubes in Figure 2-124c). 

Implementation of SFC has initially been hampered by instrumental problems, such as back-pressure regulation, need for syringe pumps, consistent flow-rates, pressure and density gradient control, modifier gradient elution, small volume injection (nL), poor reproducibility of injection, and miniaturised detection. These difficulties, which limited sensitivity, precision or reproducibility in industrial applications, were eventually overcome. Because instrumentation for SFC is quite complex and expensive, the technique is still not widely accepted. At the present time few SFC instrument manufacturers are active. Berger and Wilson [239] have described packed SFC instrumentation equipped with FID, UV/VIS and NPD, which can also be employed for open-tubular SFC in a pressure-control mode. Column technology has been largely borrowed from GC (for the open-tubular format) or from HPLC (for the packed format). Open-tubular coated capillaries (50-100 irn i.d.), packed capillaries (100-500 p,m i.d.), and packed columns (1 -4.6 mm i.d.) have been used for SFC (Table 4.27). 

Crossflow filtration membranes can be produced in flat sheet, hollow fiber, tubular formats when using polymeric materials, and in monolith and tubular configurations when using inorganic membrane materials. Table 14.2 summarizes the various module configurations. 

M. Stefansson and M. Novotny, Separation of complex oligosaccharide mixtures by capillary electrophoresis in the open-tubular format. Ana/. Chem. 66 1134-1140(1994). 

Supramolecular Assemblies from Pillararenes (Micellar, Vesicular and Tubular Formations)... 

It is not always easy to determine whether deterioration of polyurethane is caused by hydrolytic reversion or by fungal attack. However, a magnifying lens can be used to detect channel-Uke lesions on the surface of the polyurethane (this is more difficult with adhesives), and below the surface, tubular formations branch out in different directions. This network of tunnels is frequently seen to... 

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