Silica polymer-coated

Numerous applications of polymer-coated silicas to chromatography of biopolymers allow one to conclude that adsorbed or grafted hydrophilic nonionizing... 

It has been outlined by several authors that the single macromolecule may be irreversibly bound because of the large number of weakly interacting segments. The first papers on the construction of polymer-coated silica adsorbents involved the physical adsorption of water-soluble polymers. Polyethylene oxides [28, 29] and poly-/V-vinylpyrrolidone [30] are examples of the stationary phases of this type. 

Octadecylsilane (ODS) This is a polymer-coated silica packing with increased loadability of a porous silica support. Nonpolar compounds may be separated using the hydrophobic functionalities offered on ODS. 

Silica-base stationary phases have also been employed for enantiomeric separations in CEC [6,72-81]. In the initial work on chiral CEC, commercially available HPLC materials were utilized, including cyclodextrins [6,74,81] and protein-type selectors [73,75,80] such as human serum albumin [75] and ai-acid glycoprotein [73]. Fig. 4.9, for example, depicts the structure of a cyclodextrin-base stationary phase used in CEC and the separation of mephobarbital enantiomers by capillary LC and CEC in a capillary column packed with such a phase. The column operated in the CEC mode affords higher separation efficiency than in the capillary LC mode. Other enantiomeric selectors are also use in CEC, including the silica-linked or silica-coated macrocyclic antibiotics vancomycin [82,83] and teicoplanin [84], cyclodextrin-base polymer coated silicas [72,78], and weak anion-exchage type chiral phases [85]. Relatively high separation efficiency and excellent resolution for a variety of compounds have also been achieved using columns packed with naproxen-derived and Whelk-0 chiral stationary phases linked to 3 pm silica particles [79]. Fig. 4.10 shows the... 

In order to avoid the contribution of the residual silanols to solute retention, many packing materials that should not have silanols have been developed [4]. They are polymer-based materials and also polymer-coated silica phases. These polymer-based or polymer-coated phases can be recommended as very useful and stable stationary phases in LC separations of polar compounds they also offer much better stability for use at higher pH alkaline conditions. 

Recently, interest in polymer-coated silica phases has been renewed, with investigators (Chen and Lee [2]) exploring the use of more efficient deactivation techniques and more polar polymers to coat silica particles for neat CO2 chromatography. Polyethyl-eneimine-coated silica and amino-terminated polyethylene oxide-coated silica appear promising for pSFC of moderately polar basic compounds. Similarly, hydroxy-terminated polyethylene-oxide-coated silica has been used successfully for pSFC of alcohols and acids. Optimization and commercial production of these stationary phases could significantly extend the polarity range of compounds that can be chromatographed with neat supercritical CO2. 

Fig. 1 Use of polymer-coated silica stationary phase with a neat carbon dioxide mobile phase. Column Deltabond SFC Methyl (150 X 2.0 mm) mobile phase CO2 pressure gradient 75 bar initial for 2 min, then 50 bar/min ramp to 180 bar, then 15 bar/min ramp to 300 bar flow 0.5 mL/min temperature 100°C injection 5 jjlL detection flame ionization detector sample solvent methylene chloride. Peak key 1 BHT 2 dimethyl azelate 3 triethyl citrate 4 tributyl phosphate 5 methyl palmitate 6 methyl stearate 7 diethylhexyl phthalate 8 Tinuvin 327 9 Spectra-Sorb UV531 10 tri(2- ethylhexyl) trimellitate 11 dilauryl thiodipropionate ...

Packed column SFC stationary phases are very similar or identical to those used for HPLC. With neat CO2 mobile phases, polymer or polymer-coated silica stationary phases have typically been used. With modified-C02 mobile phases, bonded-phase silica columns are typically used. For structural separations, diol, amino, or cyano stationary phases are most often used. For stereochemical separations, derivatized polysaccharide-bonded silica columns are most often the stationary phases of choice. A powerful feature of modified-C02 pSFC is the ability to serially connect different stationary phases to obtain enhanced or mul-... 

Sprycha, R. et al.. Characterization of polymer-coated silica particles by microelectrophoresis, Colloid Polym. Sci., ILi, 693, 1995. 

Column 250 X 4 P-cyclodextrin polymer-coated silica (Chromatographia 1993, 36, 373)... 

Column A 100 X 4.6 Capcell pak MF [PCMF, silicone polymer-coated silica with diol and phenyl groups] (Shiseido) B Capcell pak CN (Shiseido)... 

As with SEC, two types of support materials are being used for lEC. Completely organic resins as well as surface-modified silica-gel resins are available they are listed in Table 2. TSK-DEAE 5PW [11] and Mono-Q [12] are organic polymers with surface charges. TSK-DEAE 3SW [11] is a polymer coated silica-gel, whereas... 

Figure 8. (a) Schematic picture of a polymer coated silica imprinted by 1. 

Shown below is a schematic of the interface of the polymer-coated silica fiber in contact with an aqueous solution. The illustration shows the diffusion layer thickness in the sample matrix and the thickness of the polymer film. The slope of the concentration gradients are shown at the interface between the bulk sample and polymer film surface. A steady-state diffusion... 

Table 14 Elution Volumes (IQ and Chromatographic Separation Factors (a j) for Substrates on Polymer-coated Silica Prepared using 48 as a Template...

Table 15 Capacity Factors k ) and Chromatographic Separation Factors ( y) for Imidazole and Substrates 48,50,52, and 53 on Polymer-coated Silicas Prepared using 48,50,52, or 53 as Templates...

Scheme 7.4 Schematic diagram of filler-matrix interaction in the polymer-coated silica particles (adapted from ref. 20).

Hsu, J.C. Chang, C.H. Liu, C.Y. Preparation and evaluation of a functionalized polymer-coated silica based sorbent for metal ion separation. Fresenius J. Anal. Chem. 1998,362 (6), 514-521. 

Kubeczka, K. H., 1997a. New approaches in essential oil analysis using polymer-coated silica bers. In Essential Oils Basic and Applied Research, Ch. Franz, A. Mathe, and G. Buchbauer (eds.), pp. 139-146. Carol Stream, IL Allured Publishing Corp. 

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