Dynamic coating

Another type of membrane is the dynamic membrane, formed by dynamically coating a selective membrane layer on a finely porous support. Advantages for these membranes are high water flux, generation and regeneration in situ abiUty to withstand elevated temperatures and corrosive feeds, and relatively low capital and operating costs. Several membrane materials are available, but most of the work has been done with composites of hydrous zirconium oxide and poly(acryhc acid) on porous stainless steel or ceramic tubes. 

Poole, S. K., Patel, S., Dehring, K., Workman, H., Dong, J. Estimation of octanol-water partition coefficients for neutral and weakly acidic compounds by microemulsion electrokinetic chromatography using dynamically coated capillary columns. J. Chromatogr. 

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... 

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

Capillary wall Generally, the most straightforward approach is to use an uncoated fused silica capillary. But sometimes this is not possible because of adsorption problems to the capillary wall, or other wall properties are needed to control the electroosmotic flow. In literature, there are multiple examples. Besides permanently coated capillaries, there are several descriptions of dynamic coatings available, e.g., triethanolamine, Triton X-100, Polybrene, and quaternary ammonium salts. The advantage of these dynamic coatings is that the coating can be renewed between injections, which could improve repeatability and reproducibility of the separation. 

Dynamic coating solution(s) Dynamic coating components do not always need to be added to the BGE, sometimes it suffices to flush in between runs. ... 

Lurie, I. S., Hays, P. A., and Parker, K. (2004). Capillary electrophoresis analysis of a wide variety of seized drugs using the same capillary with dynamic coatings. Electrophoresis 25, 1580—1591. 

Separation is performed using free-zone electrophoresis, where the capillary is filled with a separating buffer at a defined pH and molarity. This buffer is also called a BGE. During separation, the polarity is set to cathodic or anodic mode, also called normal and reverse mode, depending on the charge of the molecule cation or anion. For anions, the capillary is usually dynamically coated with an electroosmotic flow (EOF) modifier to reverse the EOF and separate the analytes in the co-electroosmotic mode. 

Geiser, L., Henchoz, Y., Galland, A., Carrupt, P.A. and Veuthey, J.L. (2005) Determination of pKa values by capillary zone electrophoresis with a dynamic coating procedure. Journal of Separation Science, 28, 2374-2380. 

Nowadays, the sieving matrices most employed in CSE are polymer solutions that under suitable conditions may form a transient mesh or sieving matrix that provide the size-based separation of charged biopolymers. The polymer solutions can be formulated with linear acrylamide and N-substituted acrylamide polymers, cellulose derivatives, polyethylene oxide, and its copolymers or with a variety of polymers, such as polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and hydroxypropyl cellulose(HPC), which do not necessitate the preventive coating of the capillary wall due to their ability to dynamically coat the inner surface of the capillary, resulting in suppressed EOE and sample interactions with the capillary wall. 

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