AbstractTube‐excited energy‐dispersive X‐ray fluorescence with Mo K and Ti K secondary target radiation proves to be a rapid, precise and accurate method for the multielement analysis of phytoplankton collected on membrane filters. Using 150–750 ml water samples it is possible to determine the concentration of 11–16 elements among the 22 elements which can be systematically searched for in the spectra. The study area is an estuarine water body on the Gulf of Finland and an archipelago outside th