Polymeric separation capability

One of the most important advantages of HPLC over spectrophoto-metric methods lies in its specificity and selectivity due to its separation capability. Through chromatographic separations, the analytes of interest can be detected and quantified without interference from the typical matrix that includes excipients, antioxidants, preservatives, and dissolution media. Ion-pair HPLC was used to monitor the dissolution of pentamidine from EVA sustained-release film where polymeric matrices could create significant bias if a spectrophotometric method were used. Due to their strong UV absorbance, the antioxidants and preservatives (e.g., BHA, BHT, ascorbic acid and propyl gallate) are often the major... 

Figure 3.5 Separation capability of a polymeric membrane obtained with 20% polysulfone in DMF and precipitated with a composition bath containing 50% water and 50% DMF.

In the case of the anionic polymerizability it is possible to find limits of the quantum chemical parameters which separate those monomers capable of polymerization from those not (see Table 9). 

We have demonstrated a new class of effective, recoverable thermormorphic CCT catalysts capable of producing colorless methacrylate oligomers with narrow polydispersity and low molecular weight. For controlled radical polymerization of simple alkyl methacrylates, the use of multiple polyethylene tails of moderate molecular weight (700 Da) gave the best balance of color control and catalyst activity. Porphyrin-derived thermomorphic catalysts met the criteria of easy separation from product resin and low catalyst loss per batch, but were too expensive for commercial implementation. However, the polyethylene-supported cobalt phthalocyanine complex is more economically viable due to its greater ease of synthesis. 

Reverse-phase HPLC (RP-HPLC) separates proteins on the basis of differences in their surface hydophobicity. The stationary phase in the HPLC column normally consists of silica or a polymeric support to which hydrophobic arms (usually alkyl chains, such as butyl, octyl or octadecyl groups) have been attached. Reverse-phase systems have proven themselves to be a particularly powerful analytical technique, capable of separating very similar molecules displaying only minor differences in hydrophobicity. In some instances a single amino acid substitution or the removal of a single amino acid from the end of a polypeptide chain can be detected by RP-HPLC. In most instances, modifications such as deamidation will also cause peak shifts. Such systems, therefore, may be used to detect impurities, be they related or unrelated to the protein product. RP-HPLC finds extensive application in, for example, the analysis of insulin preparations. Modified forms, or insulin polymers, are easily distinguishable from native insulin on reverse-phase columns. 

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