RP-CEC

In the RP CEC of neutral species selectivity is provided primarily by differences in the partition of the analytes between the hydrophobic stationary phase and the more polar mobile phase. There are also contributions from interactions with the silica support, the major one being polar interactions with ionised silanol groups. This is identical to the process in LC, albeit with the advantages of higher efficiencies in CEC resulting from the plug-flow profile. Additional selectivity is introduced in the case of charged species in CEC due to differences in the analytes electromobilities. 

Amino acids/peptides Glass RP-CEC Fluorescence Standards... 

ITP, isotachophoresis CZE, capillary zone electrophoresis RP-CEC, reversed-phase capillary electrochromatography lEF, isoelectric focusing OCEC, open channel electrochromatography. 

Styrene monoliths have been prepared by thermally (AIBN or benzoyl peroxide) initiated copolymerization of styrene and divinylbenzene to result mechanically stable, hydrophobic column supports for RPC as well as IP-RP-HPLC and CEC application [24,49,134-140]. 

Methacrylate monoliths have been fabricated by free radical polymerization of a number of different methacrylate monomers and cross-linkers [107,141-163], whose combination allowed the creation of monolithic columns with different chemical properties (RP [149-154], HIC [158], and HILIC [163]) and functionalities (lEX [141-153,161,162], IMAC [143], and bioreactors [159,160]). Unlike the fabrication of styrene monoliths, the copolymerization of methacrylate building blocks can be accomplished by thermal [141-148], photochemical [149-151,155,156], as well as chemical [154] initiation. In addition to HPLC, monolithic methacrylate supports have been subjected to numerous CEC applications [146-148,151]. Acrylate monoliths have been prepared by free radical polymerization of various acrylate monomers and cross-linkers [164-172]. Comparable to monolithic methacrylate supports, chemical [170], photochemical [164,169], as well as thermal [165-168,171,172] initiation techniques have been employed for fabrication. The application of acrylate polymer columns, however, is more focused on CEC than HPLC. 

Finally, when RPC methods are used in preparative studies with peptides, the opportunity routinely exists for subsequent analysis of the recovered fractions by a variety of analytical methods including high-speed RP-HPLC, HP-IEX, HP-HILIC, or HP-IMAC, zonal or micellar electrokinetic high-performance capillary electrophoresis (HP-CZE and MECK-CZE), capillary electrochromatography (CEC), or capillary isotachophoresis. The combination of the RPC information, drawn from the In k versus i > plots, with the data derived from on-line spectroscopic detection thus readily provides a comprehensive opportunity to assess the purity of an isolated peptide, many of the physicochemical features of the interaction, as well as a means to optimize the resolution in the RPC separation. 

CEC Hydrophobicity Peptide mapping and purity of peptides RP-HPLC... 

In the references to the application of CEC to biopolymers, most of the work discusses CEC-electrospray ionization (ESI)/MS, much less to direct CEC-UV/FL methods. However, much of the work has evolved from the use of commercially available, prepacked capillaries, such as Clg or ion exchange or a mixed mode containing both ion exchange and reversed phase (RP). There are very few articles that have actually attempted to develop new phases specifically for biopolymers. 

The traditional operating mode of CEC with a conventional packed column is the use of commerdally available chromatographic resins, as used for HPLC or (iHPLC. Examples are RP Qg-modified silica particles of typical diameter 3-5 pm, ion-exchange resins and stationary phases for chiral separations. The latter indude... 

COMMISSION OF THE EUROPEAN COMMUNITIES, Principles and Methods for Establishing Concentrations and Quantities (Exemption Values) below Which Reporting is not Required in the European Directive, RP-65, CEC, Luxembourg (1993). 

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