Silica polymers coated onto

Solid phase micro extraction (SPME) is a techniques in which a silica fiber coated with a thin film of polymer is brought into contact with an aqueous matrix where the organics in solution partition onto the fiber. The fiber is subsequently placed into the injector of a GC where the heat causes the release of analyte onto the column. This has been applied to endosulfan (a- and (3-) and endosulfan sulfate in water with limits of detection of less than 0.3 pg/L reported (Magdic and Pawliszyn 1996). 

Polymerization of triphenylmethyl methacrylate in the presence of a chiral anion catalyst results in a polymer with a helical structure that can be coated onto macroporous silica [742,804). Enantioselectivity in this case results from insertion and fitting of the analyte into the helical cavity. Aromatic compounds and molecules with a rigid nonplanar structure are often well resolved on this phase. The triphenylmethyl methacrylate polymers are normally used with eluents containing methanol or mixtures of hexane and 2-propanol. The polymers are soluble in aromatic hydrocarbons, chlorinated hydrocarbons and tetrahydrofuran which, therefore, are not suitable eluents. 

Figure 11. Reaction scheme for synthesis of intrinsically chiral polymer phase (CSP) and coated onto silica.

SPME uses a polymer-coated fused-silica fiber, typically 1 cm 100 m, that is fastened into the end of a fine stainless steel tube contained in a syringelike device and protected by an outer stainless steel needle. In use, the plunger of the device is depressed to expose the fiber to the sample matrix so that the organic compounds to be sorbed onto the fiber. The plunger is retracted at the end of the sampling time, and then it is depressed again to expose the fiber to a desorption interface for analysis typically by GC or LC. In a recent variation of this technique, the so-called in-tube SPME, the polymer is not coated on a fiber but on the inside of a fused-silica capillary before analysis by LC. 

They explain three types of immobilization procedures (1) physical adsorption of reagent onto the solid matrix, (2) covalent attachment of a reactive tag through a chemical bond with silanols on the silica surface, and (3) covalent attachment of a reactive tag to an organic polymer coating on the silica surface. 

One of the limitations with packed columns is eddy diffusion. This is a remixing of the separated compounds as they go around the particles in the column packing, much like you get whirlpools when water flows around a rock in a stream. To completely eliminate this problem requires the elimination of the column packing If you make the column diameter very small (< 1.0 mm), the inside wall of the column can act as the inert phase. A thin film (0.1 pm) of stationary phase is coated onto the inside of the tubing wall or even bonded to it. These capillary columns are made of fused silica and then coated with a polyimide polymer to reduce breakage. They are quite flexible and can be tied in a knot, but that is seldom done. Their natural tendency is to form a straight column, and they are hard to coil and keep... 

Using a similar TMOS/PTMOS/MTMOS system, Marx and Liron [24] templated thin silica films with propranolol. The films were spin-coated onto glass plates and the imprint removed via Soxhlet extraction with acidic methanol. Compared to a propranolol-imprinted acrylic polymer system, the sol-gel films showed lower capacity but better specificity and reproducibility. Additionally, they used radiolabeling experiments to demonstrate enantioselectivity in which the (5 )-propranolol-imprinted film was able to selectively bind 3H-(5 )-propranolol over nonradioactive (J )-propranolol, even when the (R) enantiomer was present in approximately 4000-fold excess. 

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