A study of the electrochemistry of mercury and organo mercury complexes with cysteine indicated the formation of stable complexes which can be utilized for the determination of the species in environmental matrices. A technique based on capillary electrophoresis and amperometric detection (CE-AD) has been developed for the speciation of mercury with a newly developed cross hair design electrochemical detector. This technique has the capability to detect mercury species that are electrochemically active. For CE-AD the detection limits were 0.005 +/- 0.002 mu g L-1 for Hg2+ and 0.4 +/- 0.05 mu g L-1 for MeHg+. These detection sensitivities are very attractive for environmental monitoring and the method was utilized for the determination of mercury in coal. (C) 2009 Published by Elsevier Ltd.