Chromatography

One Stationary Phase, Three Modes of Separation: Reversed Phase and Normal Phase Separations on the Same Column

Aug 05 2006

Author: Joseph J. Pesek, Maria T. Matyska on behalf of Unassigned Independent Article

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The most commonly used support material for HPLC packings are spherical, micro porous particles of silica and these are amorphous (i.e. non-crystalline) in nature. The surface of the silica particles shows poor homogeneity, being a mixture of silanols (Si-OH) of varying degrees of activity, and siloxane groups (Si-O-Si). This makes subsequent surface modifications to produce bonded phases greatly reliant on the nature of the base silica. Early silicas, made from sodium silica sols, were referred to as type A silicas. The more recent ’ultra pure’ silicas (exhibiting much lower levels of transition metal ions and better surface homogeneity - resulting in more reproducible and better chromatographic performance) , made from organic sols, are referred to as type B silicas. In this article Joe Pesek and Maria Matyska discuss a type C silica which is designed to reduce problems associated with types A&B silicas when modified.

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