Solid‐Phase Extraction

Solid-phase extraction (SPE) is a common sample preparation method that involves the interaction between an aqueous sample and a solid phase (or sorbent). An important variable in any SPE system is the choice of sorbent. Generally, SPE sorbents can be divided into two generic classes: silica-based sorbents and unmodified substrates. Irrespective of SPE format, the method of operation is the same and can be divided into several steps. Each step is characterized by the nature and type of solvent used, which in turn, is dependent upon the characteristics of the sorbent and the sample. The steps are explained in the context of a reversed-phase SPE system using a C18 sorbent, and with a vacuum manifold applied. The general methodology to be followed for off-line SPE is described using generic examples with emphasis on reversed phase, normal phase, ion exchange, and mixed mode systems.