Distinguishing catecholamines: Dopamine determination in the presence of epinephrine in water/acetonitrile mixtures

Several neural circuits within the hypothalamus, cerebellum and frontal cortex are simultaneously regulated by multiple catecholamines (CA). Yet, analytical methods that allow determination of CA either have low time resolution (microdialysis) or have poor selectivity (electrochemistry). In this study we used the structural difference between dopamine (DA) and epinephrine (EP) (primary amine group vs. methylated amine) as a distinguishable feature for the electrochemical detection of DA in DA/EP mixtures. Primary amino group of DA was activated in acetonitrile-water mixtures which provided an additional oxidation peak absent in the methylated amino group from EP. First, a systematic study of the effect of the water content in water/acetonitrile mixtures on the electrochemical response of DA is presented. It was found that the electrochemical reversibility of the main redox processes of DA is affected by the water content in acidified (1.0 mM HClO4) water/ACN mixtures. Decreasing the water content from 100% to 5% results in a progressive decrease of the DA reversibility and more importantly, promotes the appearance of a new redox signal, presumably associated to the oxidation of the amine center. That oxidation signal was used to achieve a simultaneous determination of DA and EP in water/acetonitrile mixtures (5% H2O) using square wave voltammetry. Results show an accurate determination of DA while offering an estimate of the concentration of EP. Our study opens up a new strategy for simultaneous electrochemical detection of either DA-EP or NE-EP, which in the future could be applied to surface modified microelectrodes for in vivo applications using the time resolution provided by fast-scan cyclic voltammetry, FSCV. (C) 2020 Elsevier Ltd. All rights reserved.