This paper describes for the first time the mechanism of adsorption of different dissolved mercury species onto gold surfaces directly from aqueous solutions. The surface morphology of the gold collector is critical for the adsorption behaviour of the different mercury species. Smooth gold surfaces selectively trap elemental mercury (Hg⁰), whereas nano-structured gold surfaces quantitatively retain all dissolved mercury species (Hg⁰, Hg²⁺, and MeHg⁺) from aqueous solutions. The mechanism of Hg²⁺ and MeHg⁺ adsorption can be explained by the catalytic activity of the nano-structured gold surface, whereas Hg⁰ adsorption is an amalgamation process. Nano-structured gold surfaces can easily be generated from gold collectors with smooth surfaces by adsorbing and thermally desorbing Hg⁰. Both types of gold collectors, selective collectors (smooth surface) for species specific trapping of Hg⁰ and active collectors (nano-structured) for the preconcentration of all Hg species can be used for quantitative analysis with recoveries of 97.0 ± 6.8% in ocean water after thermal desorption at 700 °C and atomic fluorescence spectrometric detection. This preconcentration method for the determination of total dissolved mercury in natural waters offers significant advantages over existing methods because no reagents are needed for sample pre-treatment, preconcentration or desorption and therefore the risk of contamination is minimized and blank values are lowered. This results in low detection limits for Hg²⁺ and MeHg⁺ of 101 pg L⁻¹ and 144 pg L⁻¹, respectively, using a sample volume of only 7 mL, and good reproducibility, with uncertainties less than 3.7% (n = 5). In addition the preparation of the active phases is very straightforward.