Chemically Bonded Layers

An ever-expanding line of special phases, many developed first for use in HPLC, are now available as a thin layer. Although their use is not widespread, there are many reasons for using them since they can be excellent scouting tools for HPLC or the reverse - taking a HPLC method and using the solvent systems on the equivalent bonded layer can give a rapid screening tool. Thus, little method development is required, with the exception of some re-ratioing of the mobile-phase components on the thin-layer plate.

The most commonly used HPLC phases are made of silica bonded with various-length alkyl chains, C18, C8, C4, CN (cyanopropyl) or aromatic rings, e.g. phenyl. All of these bonded phases are available on a TLC plate for reversed-phase chromatography. They are used as any TLC plate, but often need some organic component in the spotting solvent, since an entirely aqueous solution will not penetrate the bonded hydrophobic surface of some of these layers. The usual methanol-water, acetonitrile-water, tet-rahydrofuran-water mobile phases or other combinations of organic solvent-water with acids, bases or buffers can be used. Some highly bonded layers from certain manufacturers need a higher percentage of organic solvent to work well, and to ensure that the layers will not lift away from the support. If a higher percentage of water needs to be used with such layers, the water portion can be made up of 0.5-1 molL"1 NaCl to help the layer remain intact through the development. Some manufacturers have produced reversed-phase layers that are compatible with solvents containing up to 100% water in the mobile phase.

Other polar bonded layers, like NH2 (amino-propyl), CN and Diol (propanediol) are often used as a substitute for silica gel with the same type of - mostly nonpolar - mobile phases, but they can also be used with polar mobile phases to accomplish different separations and selectivities.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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