AbstractThe sensitivity of the determination of iron in natural waters, including seawater, using cathodic stripping voltammetry (CSV) with adsorptive collection of complexes with 1‐nitroso‐2‐naphthol is greatly enhanced by catalytic reoxidation in the presence of hydrogen peroxide. The limit of detection is lowered to 0.16 nM Fe (using an adsorption time of 60 s) and further to 0.03 nM Fe by increasing the adsorption time to 10 min. Interference from an increase in the background current, brought about by catalysis of the hydrogen evolution, is overcome by addition of an anionic surfactant (sodium dodecyl sulfate (SDS)). Optimal conditions include a hydrogen peroxide concentration of 1.8 mM and 5 ppm SDS. Procedures to purify the reagents from contaminant levels of iron are described. The method is successfully applied to certified seawater and samples from the North Atl