HPLC stationary phases monolithic

Even if MIP and BET are widely accepted regarding the characterization of HPLC stationary phases, they are only applicable to the samples in the dry state. In order to investigate the impact of polymerization time on the porous properties of wet monolithic columns, ISEC measurements of 200 jm I.D. poly(p-methylstyrene-co-l,2-bis(vinylphenyl)ethane) (MS/BVPE) capillary columns (prepared using a total polymerization time ranging from 45 min to 24 h) have been additionally evaluated (see Table 1.2 for a summary of determined e values). On a stepwise decrease in the time down to 45 min, the total porosity (St) is systematically increasing to about 30% in total (62.8% for 24 h and 97.2% for 45 min). This is caused by a simultaneous increase in the fraction of interparticulate porosity (e. ) as well as the fraction of pores (Cp). The ISEC measurements are in agreement with those of the MIP as well as BET analyses, as an increase in should be reflected in an increase in 8p and as the relative increase in the total porosity (caused by decreasing the polymerization time... 

The application of polymer monoliths in 2D separations, however, is very attractive in that polymer-based packing materials can provide a high performance, chemically stable stationary phase, and better recovery of biological molecules, namely proteins and peptides, even in comparison with C18 phases on silica particles with wide mesopores (Tanaka et al., 1990). Microchip fabrication for 2D HPLC has been disclosed in a recent patent, based on polymer monoliths (Corso et al., 2003). This separation system consists of stacked separation blocks, namely, the first block for ion exchange (strong cation exchange) and the second block for reversed-phase separation. This layered separation chip device also contains an electrospray interface microfabricated on chip (a polymer monolith/... 

Svec F (2004) Porous monoliths emerging stationary phases for HPLC and related methods. LC GC Europe 18 17... 

In order to obtain improvement in fast separations for bioanalysis by HPLC-MS/MS, the use of monolithic stationary phases may be the way. 

Section II covers the latest trends in reducing sample preparation time, including direct sample infusion/injection and on-line solid phase extraction (SPE). In Section III, we focus on newer trends in stationary phases and how these phases hope to offer different selectivities compared to current CIS-based phases. Section IV briefly provides a few observations on how new detectors are increasing the versatility of HPLC. Finally, in Section V we examine monolithic columns, small particles packed in short columns, high-temperature LC, ultra high-pressure LC, and parallel injection techniques. 

Despite the advantages of CEC over CE and HPLC, particle-packed columns are plagued with problems such as the difficulty in the preparation of frits to retain the stationary phase and bubble formation that results in current leakage and EOF breakdown. These problems set the pace for the development of column technology to overcome the problems associated with particle-packed columns and to improve on the speed of separation of analytes in mixtures. The fabrication of a continuous porous rod (monoliths), not requiring any frits and ensuring a constant and uniform current flow to give a stable EOF has so far proved a potential development for microseparations. ... 

Since 1992, a vast variety of rigid organic monolithic stationary phases with different chanistry, functionality, and column geometry has been reported for HPLC as well as CEC applications, as summarized by the number of excellent reviews [25-32,213], The development and enhancanent of monolithic stationary phases is stiU a rapidly growing area of research with scientific and industrial interest. 

Monolithic stationary phases have to be regarded as the first substantial further development of HPLC columns, as they present a single particle separation medium, made up of porous polymer. As a consequence of their macroporous structure, they feature a number of advantages over microparticulate columns in terms of separation characteristics, hydrodynamic properties, as well as their fabrication ... 

Monolithic stationary phases as a comparatively young species of HPLC column can only be accepted as a serious alternative to particle-packed columns if column robustness is in the same order of magnitude than their microparticulate counterparts. 

Table 1.3 summarizes all commercialized monolithic columns that are currently available for HPLC separation. The steadily growing number of commercially available products, based on monolithic packings, express the potential of this kind of stationary phases in particular fields of chromatography and the increasing demand from customer side. 

Li, Y., Chen, Y., Xiang, R., Ciuparu, D., Pfefferle, L. D., Horwath, C., and Wilkins, J. A., Incorporation of single-wall carbon nanotubes into an organic polymer monolithic stationary phase for mu-HPLC and capillary electrochromatography, Analytical Chemistry 77(5), 1398-1406, 2005. 

The temperature stability of monolithic stationary phases based on alkyl methacrylate monomers in capillary HPLC has also been reported [103]. These columns allowed the separation time to be reduced by over 10-fold at temperatures up to 80°C. The upper-temperature limit for these columns was not reported. 

New concepts presented in this edition include monolithic columns, bonded stationary phases, micro-HPLC, two-dimensional comprehensive liquid chromatography, gradient elution mode, and capillary electromigration techniques. The book also discusses LC-MS interfaces, nonlinear chromatography, displacement chromatography of peptides and proteins, field-flow fractionation, retention models for ions, and polymer HPLC. 

PNIPAM and its copolymers are not the only options for thermoresponsive stationary HPLC phases. Poly(acrylates) and poly(methacrylates) bearing OEG groups in the side chains are known as thermoresponsive polymers that offer some advantages over PNIPAM [40]. Such polymers were recently employed for the modification of silica monoliths, which then served as stationary phase in the HPLC separation of steroids [193], Unsurprisingly, the results were qualitatively similar to those obtained for PNIPAM-based systems, but the separation of relatively hydrophilic steroids was superior. 

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