The ions of the nuclides to be analysed in general make only a very small part of the total number of ions present in an aqueous sample. One thus needs a method concentrating the ions of interest selectively. Selective extraction can be used with liquid scintillation counting (LSC) or as a first step to make thin films by electrodeposition. Direct selective adsorption on thin films and subsequent measurement with a semiconductor detector avoids time consuming and expensive chemical steps. Energy resolution is still far better than with liquid scintillation measurements. (units)