Continuous gradient

Figure 2. CM-cellulose chromatography of pectolytic enzymes. The activity peaks of the flow-through of a DEAE-cellulose chromatography was applied to a CM-cellulose column. The column was eluted with a NaCl (0-0.5M) continuous gradient at a flow rate of 34 ml/h. 10 ml fractions were collected and assayed for pectolytic activities Symbols (0) pectate lyase ( ) polygalacturonase (reducing sugar-releasing activity) (x) protein. Other details in Methods.

In situ loading during the chromatographic development. By this method a continuous gradient of the hquid stationary phase is created on the PLC layer in the direction of the mobile phase flow. This is achieved by developing the plate with a suitable multieomponent solvent system. 

The device for continuous gradient elution in horizontal chamber described by Nyiredy [15] and presented in the preceding text, (Figure 6.10) seems to be a very interesting solution both for analytical and preparative applications. 

Because there is no back-mixing of fluid elements along the direction of flow in a tubular reactor, there is a continuous gradient in reactant concentration in this direction. One does not... 

This very large selectivity or relative retention, makes normal isocratic elution (constant eluent composition) inappropriate. Instead, gradient elution or stepwise elution are used. The eluent pH or ionic strength is changed either in a continuous gradient or in a series of steps to desorb and so elute one protein, or group of proteins, at a time. An example of stepwise elution is shown in Figure 19.9. 

The presence of a low-viscosity interfacial layer makes the determination of the boundary condition even more difficult because the location of a slip plane becomes blurred. Transitional layers have been discussed in the previous section, but this is an approximate picture, since it stiU requires the definition of boundary conditions between the interfacial layers. A more accurate picture, at least from a mesoscopic standpoint, would include a continuous gradient of material properties, in the form of a viscoelastic transition from the sohd surface to the purely viscous liquid. Due to limitations of time and space, models of transitional gradient layers will be left for a future article. 

Fig. 1 Illustration of a 2D continuous gradient combinatorial library that exhibits gradual and systematic changes in two variables...

The correlation of residence time to reaction time is critical in the ability to treat the volume of the channel as a continuous gradient in molecular mass. ATRP is particularly well-suited to this type of device because the reaction can be initiated at a fixed mixing element at the head of the channel where a catalyst and initiator can be brought together. By replacing a small molecule initiator with a polymer chain capable of being reinitiated, copolymers could be prepared. This was done in the thiolene/glass devices with a poly(n-butyl methacrylate) block... 

It is possible to combine stepwise gradient and continuous gradient, i.e., the starting elution buffer has a higher ionic strength than the binding buffer, and after a short time the elution of the protein(s) of interest starts by application of a flat continuous gradient. 

Density gradients maybe divided into three types preformed discontinuous gradients (e.g.. Protocol 5.3.1), preformed continuous gradients (e.g.. Protocol 5.3.2) or self-generating gradients (e.g.. Protocol 5.3.3). Materials used for density gradients are classified as ionic and non-ionic media (Table 5.1). 

Isocratic elution is performed with a single solvent (or constant solvent mixture). If one solvent does not provide sufficiently rapid elution of all components, then gradient elution can be used. In this case, increasing amounts of solvent B are added to solvent A to create a continuous gradient. 

Vleugels, J., Anne, G., Put, S., Van der Biest, O., (2003), Thick plate-shaped Al203/Zr02 composites with a continuous gradient processed by electrophoretic deposition , Mat. Sci. Forum., 423 125, 171-176. 

We have found that ethanol works well for this purpose. When microparticle-packed HPLC columns are used, the solvent change must be accomplished as a gradual, continuous gradient. Discontinuous increments (step gradients) tend to cause rapid viscosity and thermal changes along the column bed these are known to cause destruction of the bed. 

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