Results of the 1997/98 interlaboratory comparison on the determination of I-131 in milk.

Following the accident in Chernobyl in 1986 the number of equipments available for monitoring radioactivty, especially for gamma spectrometry, has been increased considerably in the Federal Republic of Germany. Futhermore, new legislation requires that all official monitoring laboratories verify the quality of their analytical technique by participating in interlaboratory comparison studies organized by Federal institutions. Such a study was therefore organized in 1997/98 by the Institute of Chemistry and Physics at the Federal Dairy Research Centre Kiel. 79 laboratories collaborated on the analysis of I-131 in milk. This paper describes the statistical evaluation of 101 sets of data for I-131, 15 sets for I-131 pre-concentrated with an anion exchange resin and 60 sets for K-40. As expected the results of the study were good. After eliminating a few discordant data, the average deviation of the laboratory means from the overall mean was 5.5 % for I-131: 7.0 % for pre-concentrated I-131 and 4.0 % for K-40. Such good results imply that experienced personnel are efficiently operating modern sophisticated equipment and software.