Methods for measuring dopamine release

HPLC with electrochemical detection

Biological samples are mixtures of many compounds. The assay of biological samples usually begins with separation of the mixture into its components. Classically, dopamine and its metabolites have been separated from tissue samples by extraction into organic solvents or by ion exchange. During the past 25 years, the preferred method of separation of dopamine and its metabolites has been HPLC. Using this technique, dopamine, its acidic metabolites, and its amino acid precursors can be separated from extracts of brain tissue, or in samples of extracellular fluid acquired by cerebral microdialysis. Once this separation has been obtained, the separate analytes must be detected by some means, either due to the presence of a radioactive label, or on the basis of some other inherent property.

The chemical structure of dopamine is based upon catechol, an aromatic ring in which two adjacent ring protons are replaced with hydroxyl groups. The catechol structure imparts critical properties related to the interactions between dopamine and its receptors, but also reduces the chemical stability of molecules bearing it. The catechol group is highly oxidizable, meaning that electrons are readily withdrawn by other molecules or by catalytic surfaces. Exposure of a catechol to an electric field with a potential difference of one volt causes an oxidation reaction in which four electrons are transferred to the surface of the electrode, with the production of an oxidized quinone molecule.