The electrochemical behaviour of a Fe(III)/Fe(II) redox couple in the presence of various amino acids and neurotransmitters such as monoaminergic neurotransmitters (dopamine, adrenaline and noradrenaline) has been studied. Ammonium iron(II) sulfate served as a source of iron. Solubility required that studies being conducted at low pH values. Cyclic voltammetry experiments revealed the capability of amino acids and neurotransmitters to interact with free iron and, hence, change its electrochemical behaviour. In addition to confirm complexation reactions occurring between Fe(II) and amino acids and neurotransmitters potentiometric studies have been carried out. Calvin-Bjerrum pH-titration technique as used by Irving and Rossotti has been applied to determine stability constants at 25 degrees C. (C) 2014 Elsevier Ltd. All rights reserved.