Dynamic-coating method

To improve the success of the dynamic coating method, Schomburg suggested a modification of the above method, known, as... 

A second simpler method that has been used to eliminate EOF is to mask the surface silanol groups using an adsorbed polymer. This self-coating or dynamic-coating method will be discussed in more depth in a later section of this chapter. 

Dynamic coating appears to he especially attractive for plastic microchips, as estahhshed surface chemistry such as silanization is often not apphcahle to polymeric materials. Permanent coatings are often regarded as the most effective way to perform surface modification in order to reduce analyte-wall interactions and to modify elec-troosmotic flow (EOF). Permanent surface modification is, however, often more laborious in the production process and might, accordingly, be less attractive for disposable devices. Dynamic coating methods are applied not only to control EOF and reduce analyte adsorption but also to make a hydrophobic surface more compatible with a hydrophilic separation medium. 

Yan s group reported the first example of MOF-coated capillary column for high-resolution GC separation. MIL-101 was chosen as the stationary phase, and the MIL-101 crystals were coated on the capillary column by a dynamic coating method. A slurrylike suspension solution of MIL-101 is first filled into the capillary under gas pressure, and then pushed through the capillary at a steady speed, leaving a wet coating layer on the... 

The paper discusses the application of dynamic indentation method and apparatus for the evaluation of viscoelastic properties of polymeric materials. The three-element model of viscoelastic material has been used to calculate the rigidity and the viscosity. Using a measurements of the indentation as a function of a current velocity change on impact with the material under test, the contact force and the displacement diagrams as a function of time are plotted. Experimental results of the testing of polyvinyl chloride cable coating by dynamic indentation method and data of the static tensile test are presented. 

Carbowax 20M, polysiloxanes, and N-cyclo-3-azetidinol are the most widely used sutetances for the thermal degradation method [143,180,192-194]. In the case of the Carbowax treatment deactivation can be carried out in either of two ways. The column can be dynamically coated with a solution of Carbowax 20H in a volatile solvent, excess solvent evaporated with a stream of nitrogen, the column ends sealed and the column heated at about... 

CZE-ELD, with a Au microelectrode at —0.6 V vs. SSCE and a Pt wire as auxiliary electrode, using sodium borate buffer and dodecyltrimethylanunonium bromide for dynamic coating of the capillary internal surface, can be applied for separation and determination of ultra-trace amounts of many oxidizing substances. Thus, the concentration of peroxodisulfate (S208 ) and peroxomonosulfate (S05 ) ions in pickling baths can be monitored by this method. The faster emergence of the heavier peroxodisulfate ion is attributed to different adsorption of the two analyte ions by the capillary coating . ... 

In contrast to the various CSPs mentioned so far, but still based on covalently or at least very strongly adsorbed chiral selectors (from macromolecules to small molecules) to, usually, a silica surface, the principle of dynamically coating an achiral premodified silica to CSPs via chiral mobile phase additives (CMPA) has successfully been adapted for enantioseparation. The so-called reverse phase LC systems have predominantly been used, however, ion-pairing methods using nonaqueous mobile phases are also possible. 

Liquid chromatography is two decades more mature than capillary electrophoresis. As trained electropherographers become more common, more separations will be handled by electrophoresis. For example, electrophoresis displaced liquid chromatography as the preferred method for forensic analysis of alkaloids in opium and heroin.51 The enabling technology for this application was dynamic coating of the capillary between runs to eliminate adsorption of analytes on the silica surface and decrease variations in migration times to less than 0.5%. 

Schulze et al. [135] developed fused-silica chips dynamically coated with hydroxypropylmethyl cellulose and utilized them for the separation of aromatic low molecular weight compounds such as serotonin, propranolol, a diol, and tryptophan. The authors used deep UV laser-induced fluorescence detection for these compounds. Schuchert-Shi et al. [136] identified ethanol, glucose, ethyl acetate, and ethyl butyrate, byproducts obtained in enzymatic conversions using hexokinase, glucose oxidase, alcohol dehydrogenase, and esterase. The authors reported that the quantification for ethyl acetate was possible using contactless conductivity detection. Hu et al. [137] described the separation of reaction products of (3-thalassemia in a multiplex primer-extension reaction using NCE. The method developed was used for patient samples and the results coincided with those of a detection kit. 

In this reversed phase high performance liquid chromatographic method for neutral and cationic metal chelates with azo dyes, tetraalkylammonium salts are added to an aqueous organic mobile phase. The tetraalkylammonium in salts are dynamically coated on the reversed stationary support. As a result of the addition of tetraalkylammonium salts, the retention of the chelates is remarkably reduced. Tetrabutylammonium bromide permits rapid separation and sensitive spectrophotometric detection of the vanadium(V) chelate with 2-(8-quinolylazo)-5-(dimethylamino)-phenol, making it possible to determine trace vanadium(V). 

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