Combined ion-pair extraction and high-performance liquid chromatography for the determination of the biogenic amines and their major metabolites in single brain tissue samples

A combined procedure based on reversed-phase liquid chromatography with electrochemical detection has been developed for the determination in the picomole range of the monoamines dopamine, norepinephrine, epinephrine and serotonin, and their major metabolites 3,4-dihydroxyphenylacetic acid, homovanillic acid, 3-methoxy-4-hydroxyphenylethylene glycol, 5-hydroxyindoleacetic acid, normetanephrine, metanephrine and 3-methoxytyramine. Sample pretreatment consists of the extraction of the neutral and acidic metabolites with ethyl acetate, followed by the extraction into heptane of the catecholamines with tetraoctylammonium bromide as counter-ion in the presence of diphenylborate. The residual supernatant is directly injected in the chromatographic system for quantification of serotonin, normetanephrine, metanephrine and 3-methoxytyramine.