Inter-comparison of radium analysis in coastal sea water of the Asian region

• Lab inter-calibration is for assessing the accuracy of the analytical data.
• Most of the data reported by labs is within two standard deviations of the mean.
• The labs measured 226Ra with a relative confidence interval of 6–11%.
• A significant difference was higher extraction efficiency for the Asian exercise.

Laboratory inter-comparison is one of the methods used for regularly assessing the accuracy of the analytical data produced by laboratories for particular measurements. A working group at the 2010 GEOTRACES Asia Planning Workshop in Taipei recommended that a Ra inter-comparison experiment be conducted in the surface sea water of the Asian coastal region. In May 2011, we organized the Asian Ra Inter-comparison experiment. Analytes included 223Ra, 224Ra, 226Ra, 228Ra, and 228Th. Nine laboratories joined this activity. One sample set was collected in the coastal region of the Yellow Sea, near Qingdao, China (YS1, YS2) and another in Tolo Harbor of Hong Kong (HK1, HK2). These waters are relatively high in Ra and low in suspended matter and can be considered representative of coastal waters in the region. The results show that most of the data reported by different labs is within two standard deviations of the mean. Radium extraction efficiencies based on two Mn-fiber columns attached in series averaged 95–99%. Results for 226Ra, 223Ra, and 228Th in the Asia Inter-comparison are considerably less scattered than in the GEOTRACES Atlantic Inter-comparison. For 228Ra the Asia and GEOTRACES results are similar; but for 224Ra, the Asia results are considerably more scattered than the GEOTRACES results.