INDIRECT DETERMINATION OF SOLUBLE TRACE-ELEMENTS IN CERTIFIED REFERENCE MATERIALS BY NEUTRON-ACTIVATION ANALYSIS

Since 1983 we have analyzed aqua regia extracts from environmental ref erence materials of 5 different soils and 4 different sludges by neutr on activation analysis. Aqua regia as such is not accepted for irradia tion in a nuclear reactor, and therefore the solution has to be evapor ated to dryness, mixed and dried to constant weight before an aliquot can be taken and subjected to instrumental neutron activation analysis (INAA). Results for leachable Cr and Zn were found to display greater variability than results for total contents of these elements, and th e reasons for this will be discussed. For the 1994 certification campa ign for one soil and two sludges we have chosen to determine the total content of trace elements in these reference materials by INAA before and after aqua regia leaching. The leachable contents are then found indirectly as a difference between the two results; in this way we eli minate the sources of uncertainty associated with the drying and handl ing of the aqua regia extracts, and we reduce the contributions from c ounting statistics.