137Cs low-level determination in drinking water using a silica gel impregnated with molybdophosphate (ASG adsorbent)

137Cs released to the biosphere has to be determined in water samples to study subsequent pathways of this element to man. This radioisotope is usually only present in drinking water at extremely low concentrations and complex radiochemical procedures are necessary before the 137Cs concentration can be determined by gamma ray spectrometry. In this paper, an improved method has been developed in order to reduce the cost of analysis and the required time. In this procedure 137Cs is removed from water by using adsorption on silica gel impregnated with molybdophosphate (ASG adsorbent). The analytical procedure has been validated according to the quality requirements of the ISO 17025 Standard by evaluating the following parameters: selectivity, minimum detected activity (MDA), precision, accuracy and expanded uncertainty. The method has been applied to different samples taken from the Barcelona (Spain) water supply. (orig.)