Macromolecule Collector

It had been discovered very early that macromolecule compounds can be used as flotation collector. For example, gelatin is the collector of quartz. Casein can be used as the collector of feldspar and quartz. The main ingredients of gelatin and casein are proteins and amino acids. The flotation results of feldspar and quartz using amino acid are shown in Fig. 2.4. 

Cellulose xanthate can be used as flotation collector, too. The structure of cellulose xanthate can be expressed as follows  

It was reported that cellulose xanthate was used to flotate silicate mineral from hematite. And it was a substitute for xanthate in Japan during World War n. The flotation performance of cellulose xanthate is worse than that of xanthate in the flotation of copper sulflde ore. 

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In filtration, the particle-collector interaction is taken as the sum of the London-van der Waals and double layer interactions, i.e. the Deijagin-Landau-Verwey-Overbeek (DLVO) theory. In most cases, the London-van der Waals force is attractive. The double layer interaction, on the other hand, may be repulsive or attractive depending on whether the surface of the particle and the collector bear like or opposite charges. The range and distance dependence is also different. The DLVO theory was later extended with contributions from the Born repulsion, hydration (structural) forces, hydrophobic interactions and steric hindrance originating from adsorbed macromolecules or polymers. Because no analytical solutions exist for the full convective diffusion equation, a number of approximations were devised (e.g., Smoluchowski-Levich approximation, and the surface force boundary layer approximation) to solve the equations in an approximate way, using analytical methods. 

The important issue of 2D-LC represents the abovementioned transfer of column effluent between the Id and the 2d columns, which can be done either off-line or online. In the off-hne approach, the fractions from the Id column are collected and successively re-injected into the 2d column. In this case, the unit TF is just a fraction collector. The macromolecules within particular fractions from the Id column are immixed so that resulting overall separation selectivity may be challenged. Moreover, entire procedure is laborious and slow. Various approaches were elaborated for the online transfer of fractions from the Id column into the 2d column. Often, the fractions from the Id column are cut into small parts that are one-by-one gradually transported into the 2d SEC column for independent characterization. This is the method of choice if the first-dimension separation produces broader peaks, such as it does liquid chromatography under critical conditions of enthalpic interactions, LC CC (see section 11.8.3). The operation principle of such chop-and-reinject method is evident from Figure 22. In this case, the TF unit from Figure 21 is a switching valve. 

In each technique, the eluate from the separation column is collected as a series of fractions by a fraction collector. The resulting enzyme solutions are concentrated to a smaller volume for the following determination. For the purpose of reduction in volume, ultrafiltration can be easily and rapidly performed membranes with different porosities, which will retain the chosen macromolecule while being permeable to the solvent and to small molecules, are commercially available. 

Here, we consider the two general approaches to coat colloidal particles with ultrathin film tunable in nanometer range. These methods differ by class of species employed for shell buildup, type of used colloidal particles and conditions for shell fabrication. First one is layer-by-layer (LbL) assembly of oppositely charged macromolecules or nanoparticles, which emanates from LbL assembly on macroscopic flat films developed in the early nineties by Decher and co-workers. Another approach is controlled precipitation of macromolecules or nanoparticles from the solution on surface of micron and submicron sized colloidal particles. The surfaces of these particles serves as collector for precipitating materials. 

Four of the entries shown in the comment column of Table 3 for macromolecules also indicate that problems exist. The subjects of the first, tenth and thirteenth entries in Table 3, namely sample pre-treatment procedures, choice of detector and collection of separated fractions, are all connected in that they arise from the complexity of the analyte mixtures, a subject discussed previously. The subject of the first entry constitutes the major, at present unsolved, problem in the separation of macromolecules. As a result it may be confidently predicted that much of the instmment manufacturers research and development efforts at the present time lies in this area of automated sample pretreatment devices suitable for mixtures of macromolecules because this area must be automated if the whole HPLC process is to be automated. The problem indicated in the tenth entry of Table 3, concerning the choice of detector for macromolecules was also discussed in the previous part. Therefore it is sufficient to note here that because of the lack of a universal, sensitive detector for macromolecules two or more of the available detector molecules, arranged in tandem, may need to be employed. Alternatively if a single detector module of the type already discussed in the previous section is used, then discrete fractions of the eluate must be collected for subsequent off-line analysis by say, gel electrophoresis, immuno- or bio-assay procedures. This alternative practice accounts for the optional entry number 13 in Table 3 regarding the provision of a fraction collector. 

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