BRAIN-TISSUE AND PLASMA ASSAY OF L-DOPA AND ALPHA-METHYLDOPA METABOLITES BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ELECTROCHEMICAL DETECTION

Using reverse phase high‐performance liquid chromatography and electrochemical detection with mobile phases composed of simple acids, we have developed an assay technique to measure multiple catecholamines and their catechol metabolites in plasma or brain tissue with sensitivity to the picomole level. Ion‐pairing chromatography with nitric or trichloroacetic acid as the mobile phase permits separation and quantitation of norepinephrine, α‐methylnorepinephrine, epinephrine, dopamine, α‐methyldopamine, l‐DOPA, α‐methyldopa, carbidopa, and DOPAC. Alumina extraction selectively isolates catechols which are then separated on a reverse‐phase column and measured by a commercially available electrochemical detector. This method has been applied to measurement of L‐DOPA metabolites in patients with Parkinson's disease treated with L‐DOPA and carbidopa and to measurement of catecholamines in rat hypothalamus in the course of studies on L‐DOPA and α‐methyldopa metabolism. Dihydroxybenzylamine is added as an internal standard and standard curves are linear over two orders of magnitude in concentration with coefficients of variation averaging 3.1%. Quantitation is routinely done to 20 pmol with absolute sensitivity possible to 0.5 pmol. Copyright © 1979, Wiley Blackwell. All rights reserved