A Rational Approach to the Development of Solid Phase Extraction Methods for Drugs in Biological Matrices

Summary

There are many types of solid phase extraction cartridge, and many different priming, washing and eluting solvents can be used. So many are the possibilities for a new assay that sensible choice of available options may appear impossible. Whilst a method of extraction can usually be developed quickly, especially if the ubiquitous C18 phase is used, a more selective and robust method can usually be achieved if a range of options is properly explored.

An approach that fulfils this is presented. The scheme includes:

• 1. Identification of extraction requirements;

• 2. Screening of cartridges to identify effective phases;

• 3. Optimisation of adsorption, rinsing and elution stages to achieve best selectivity and robustness;

• 4. Validation for routine application.

The need to consider all phases and achieve a contrast with subsequent chromatography is emphasised. The utility of the approach is illustrated for different types of drugs and metabolites.