Monolithic media

Despite a growing number of applications in various areas, separations in the HPLC and CEC modes remain the focus of almost all groups working with the monoliths. Since the use of monolithic media in CEC has been summarized recently in several review articles [42,107,113,114], we will focus in this chapter only on the HPLC separations. 

The most important feature of monolithic media is that the mobile phase flows exclusively through the separation unit. In contrast, there is no flow inside the conventional porous chromatographic particles and only a partial flow through the perfusion beads. Just as with the membrane adsorbers, monolith stationary phases may be operated with a minimum in mass transfer resistance with the concomitant advantages in terms of speed and throughput. 

These examples clearly demonstrate the benefits of the facile tuning of surface chemistry afforded by the monolithic media. The wealth of commercially available monomers possessing a wide variety of functionalities, together with the extreme simplicity of the preparation of the monolithic columns, makes this approach an appealing option for the design of capillary columns with high selectivities. 

If you need a water-ricli mobile phase think of the newest AQ-phases (eg. YMC AQ, AQUA, Platinum EPS), monolithic media, shield phases, hybrid phases or the old workhorses such as Nucleosil iOO, Bondapak. LiChrospher... 

Combine a normal gradient (increase in the eluent strength) with a flow gradient in one step. Use short columns for this, or use monolithic media. 

Silica gel from most manufacturers is, after a thorough acid wash with HCl or H2SO4 at low temperature, for the most part clean and metal free. New approaches are silica gel made from alkoxysilanes to get a pure material (e.g. Symmetry, Purospher) and monolithic media (SilicaROD). 

Ro KW, Nayalk R, Knapp DR (2006) Monolithic media in microfluidic devices for proteomic. Electrophoresis 27 3547-3558... 

Since the publication of the third edition in 2004, considerable effort has been focused on the development of monolithic separation materials for use in ion chromatography. Monolithic media offer the potential benefit of faster analysis or improved resolution with comparable analysis speed, thus following the trend toward shorter analysis times observed in conventional liquid chromatography. While method speedup in conventional liquid chromatography (UHPLC) is achieved by utilizing smaller particle sizes and smaller column formats, this pathway can be followed only to a certain extent in ion chromatography due to the limited back pressure tolerance of metal-free components in the fluidic... 

This new synthesis method provides an improved means of preparing monolithic media compatible with stationary-phase synthesis techniques developed for particulate media. The new technique is compatible with polymeric column hardware and does not require covalent bonding of the monolith to the inner column wall. The use of prepolymerized particles circumvents issues associated with shrinkage problems that are characteristic of conventional monolith syntheses (see Section 3.4.1.6) while providing excellent efficiency for small-molecular weight anions, even under isocratic conditions. 

The most widely used polymer monoliths are poly(styrene-co-divinylben-zene)-based monoliths and moderately polar monoliths based on methacrylic acid esters. While the first ones are strongly hydrophobic materials prepared by polymerization of styrene and its derivatives with divinylbenzene as the cross-linking agent [323,324], methacrylate-based monoliths are synthesized by polymerization of butyl methacrylate or other methacrylic acid esters with ethylene dimethacrylate as the cross-linking agent [325,326]. These types of monolithic media in capillary format are the main focus of a very detailed review by Urban and Jandera [327]. 

More recently, coating techniques were also developed to create Pd-derived supports, which provided a simpler approach to be put into use compared to grafting techniques. The use of poly(Af,M-di(pyrid-2-yl)norborn-2-ene-5-yl-carbamide) and H2PdCl4 coatings on monolithic media has been shown to... 

Metathesis The first successful use of ROMP-based monolithic media for heterogeneous catalysis was accomplished by employing these supports as carriers for the Grubbs ruthenium initiator based on NHC Ugands [135, 136]. In order to generate sufficient porosity, monoliths with a suitable microporosity (40%) and micro-globule diameter (1.5 0.5 pm) were synthesized. Consecutive in situ derivatization was successfully accompUshed using a mixture of NBE and a polymerizable NHC precursor (Scheme 11.12) [23, 98,137-139]. 

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