Introduction

In the early days of liquid chromatography (LC), the most commonly used stationary phase was silica gel, which was usually loaded with water and employed with a hydrocarbon mixture such as petroleum ether as the mobile phase. To change the selectivity of the distribution system, the hydrocarbon was sometimes adsorbed on the silica, and water or an aqueous alcohol mixture was used as the mobile phase. For obvious reasons, the latter was termed a reversed-phase system. Since that time, the reversed phase has been defined in a number of different ways: in this article, it is regarded as consisting of hydrocarbon moieties chemically bonded to a silica matrix. Reversed phases are considered to exhibit predominantly dispersive interactions with any solute or solvent with which they are in contact.

The first reversed phase was synthesized by Halasz and Sebastian in 1969 by refluxing silica with a suitable alcohol (e.g. n-octanol) to form the silyl ester, the hydrocarbon chain being linked to the silica by carbon-oxygen-silicon bonds. This bonding proved to be labile, as the hydrocarbon moiety was easily removed by hydrolysis, but was sufficiently stable to allow the potential of such phases to be established. The next year Kirkland and DeStefano used chloro-silane reagents to attach the hydrocarbon chain to the silica by a silicon-oxygen-silicon bond which proved to be far more stable, at least between pH 4 and pH 8.

Subsequently, other silyl reagents, such as the silyl esters, were also shown to react with silica. Some of these reagents are now commonly used in the production of reversed phases.

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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