HPLC packings

CEC is often inappropriately presented as a hybrid method that combines the capillary column format and electroosmotic flow employed in high-performance capillary electrophoresis with the use of a solid stationary phase and a separation mechanism, based on specific interactions of solutes with the stationary phase, characteristic of HPLC. Therefore CEC is most commonly implemented by means typical of both HPLC (packed columns) and CE (use of electrophoretic instrumentation). To date, both columns and instrumentation developed specifically for CEC remain scarce. 

The simplest way to eliminate the problems of porous particles is to eliminate the pores. Nonporous particles of 10 pm diameter with a thin layer of stationary phase on their surfaces were in fact introduced early in the evolution of HPLC packings as a solution to the pore problem, but achieved little popularity because of their low capacity. Recently, nonporous materials have returned to the marketplace in the form of very small particles with diameters of 1.5 to 2.5 pm. The use of small particles compensates to some extent for the loss in capacity.11 However, because of the high flow resistance of microparticulate nonporous packings, they are generally packed in short lengths and often operated at elevated temperatures. 

Assay of proteins using wide-pore HPLC packings... 

Interaction of naproxen with the surfaces of silica gel and ODS silica gel HPLC packings. 

M. Verzele, Trace metals in silica gel-based HPLC packing materials, LCMag., 7 217 (1983). 

One important application of Fl-FFF is the determination of the particle size distribution of chromatographic silica for HPLC packings [226,428,429] which, in combination with S-FFF, allows characterization of the porosity of the samples and particle size distribution. 

We now have a fairly adequate understanding of the different properties, including the particle diameter i/p, the pore size, the degree of permeability, and the chemical composition of the surface of the support matrix, to know which type of stationary phase can be successfully used with a particular class of peptides. Most of the HPLC packing materials now in use for peptide separations are based on the wide pore microparticulate silica gels with polar or nonpolar carbonaceous phases chemically bonded to the surface of the matrix. Methods for the preparation of these chemically bonded stationary phases, their available sources of supply. 

Nonpolar, porous polystyrene-divinylbenzene (PS-DVB) copolymers have also been used (4 /, 45a) as re versed-phase HPLC packings for peptide separations. Compared to the chemically bonded n-alkyl silicas, these supports show generally much lower efficiencies. As they can, however, be used over a wide pH range, e.g., Amberlite XAD-4 can be used over ca. pH 1.5-12.5, these types of supports could find limited use in situations where pH control of the selectivity is mandatory. 

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