Solid-phase extraction in clinical biochemistry

In order to measure low concentrations of analytes in plasma and urine, it is often necessary to extract and concentrate them. With solid-phase extraction (SPE), this is achieved by partitioning the analytes between a solid and a liquid or headspace vapour. A wide range of high-quality materials is now available to do this, offering a variety of separation modes for different applications. These include partitioning using reversed-phase, normal-phase, ion-exchange, restricted-access and immunoaffinity sorbents or molecularly imprinted polymers and, increasingly, combinations of these processes. Solid-phase microextraction was introduced to analyse volatile and semi-volatile compounds. The range of sampling formats has expanded from simple packed syringes to cartridges, disks, SPE pipette tips and 96-well plates. These developments have facilitated automated off- and on-line sample processing. The basic principles of SIDE and the recent innovations are reviewed here. This is a technological growth area. Some of the developments are finding application in clinical toxicology. However, they could also be of wider value in clinical chemistry for example, for analyses of volatile and non-volatile metabolites, peptides, radioactive elements and trace metal speciation.