Polymeric column

Figure 1.2 illustrates the different process impurities present in a sample of erythromycin [11]. A polymeric column was used. 

Another type of synthetic polymer-based chiral stationary phase is formed when chiral catalyst are used lu initiate the polymerization. Columns of this type (c.g.. Chiralpak Of) are available front Chiral Technologies, Inc., or J. T. Baker Inc. 

Fig. 10 Chromatogram of a pigment extract form a natural seawater sample on a polymeric column (Vy-dac 201 TP). Mobile phases (a) methanol-pyridine (0.025 M, pH adjusted to 5.0 with acetic acid) (80 20, v/v) (b) acetontrile-acetone (70 30, v/v). (From Ref. 77.)...

Do not try to open or repack polymeric columns. They are usually under some pressure and come out of the tube like toothpaste. The column is of no use. Polymeric columns are usually packed in one solvent, then switched to a second solvent, which causes the packing to swell and squeeze out voids. They are then designed to be run in the second solvent. Polymeric ion exchangers are usually run at elevated temperature. This serves two purposes it decreases mobile phase viscosity, thereby reducing operating pressures, and it speeds... 

Both polymeric and silica-based columns are in common use.The polymeric columns are heavily used in the analysis of synthetic polymers and plastics where organic solvents are required. Silica-based columns with hydrophilic bonded phases are used to separate aqueous solutions of macromolecules. Finally, polymeric size-separation columns with hydrophilic phases are available for separation of polysaccharides, peptides, and very small proteins. 

Each column type has its own place of use. Column variety is what gives HPLC its versatility. It really depends on your compound and application. Approximately 80% of all separations are done on 5-10-jUm reverse phase Ci8 silica columns. Much of this is tradition. Reverse phase columns offer high-resolution separations for a wide variety of compounds and can be run in aqueous mobile phases. Ion exchange separations require salt solutions for separations, and these are not compatible with mass spectrometers. Size separations have lower resolving power and longer run times, but may be the only way to separate proteins solutions that will irreversibly stick to reverse phase columns. Use small pore size separation columns to remove salt from effluent from other chromatography separations. Zirconium and polymeric column are newer and offer possibilities for unique separations. 

P. D. Bryan and J. T. Stewart, Separation of tetracyclines by liquid chromatography with acidic mobile phases and polymeric columns, J. Pharm. Biomed. Anal., 77 971 (1993). 

A few polymeric reversed-phase stationary phases are available which provide the advantage that they can be operated over a wider pH range than the silica-based columns. Polymeric columns, however, tend to be less efficient than silica-based ones and are often less retentive. 

Eluent pH is limited to a maximum of 7 to 8 due to the reduced chemical stability of a chromatographic bed in an alkaline medium. The nucleophilic attack of Si-0 bonds by hydroxide ions leads to the erosion of the silica surface as shown by back pressure increases caused by the formation of Si(OH)4. With polystyrene-divinyl-benzene-based stationary phases, pH stability is not an issue and a very wide mobile phase pH range can be used, thereby providing additional selectivity [1]. Several silica-based and polymeric columns claimed to be stable in pH ranges from 1 to 13 are commercially available, however, they are not commonly used. 

Chelating solutes—trace metals in base silica. —> Use high purity silica-based column with low trace-metal content, add EDTA or chelating compound to mobile phase use polymeric column. 

Absorption or adsorption of proteins. Reduce nonspecific interactions by changing HPLC mode add protein-solubilizing agent, strong acid or base (with polymeric columns only), or detergent such as SDS to mobile phase. 

With the columns improved as recommended above, it is desirable to repeat many off-line experiments performed earlier. To avoid necessity of extra corrections, it is preferable to simultaneously chromatograph as many elements as possible, and to run experiments with this mixture under various experimental conditions. In particular, because our major concern is the column surface, of great interest would be experiments in the columns made of metals or temperature-resistant fluorinated polymers. The polymeric columns remain unemployed in gas-phase radiochemistry. Their surface will probably not be modified, which can lead to unexpected phenomena or regularities. 

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