IOCCP-JAMSTEC 2018 Inter-laboratory calibration exercise of a certified reference material for nutrients in seawater

AOYAMA MICHIO; 82 AUTORES MÁS; SOLIS M.E.; 20 AUTORES MÁS

Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

Año: 2018 p. 214

978-4-901833-37-0

In 2017, the International OceanCarbon Coordination Project (IOCCP) and the Japan Agency for Marine-EarthScience an Technology (JAMSTEC) decided to conduct the 6th InternationalInter-Calibration Exercise, the ?2017/18 inter laboratory comparison exerciseof Certified Reference Materials of Nutrients in Seawater, CRM?. As was thecase with the previous four inter-comparison (IC) studies organized by MRI-JMAand the previous IOCCP-JAMSTEC IC exercise in 2015, the aim of this IC exercisewas to improve the level of comparability by exchanging knowledge amongparticipating laboratories. The scale of the study was expanded. One hundredseven laboratories in 33 countries across five continents received a letter ofinvitation to the IC exercise, and 71 laboratories in 30 countries agreed toparticipate in this IC exercise. Results were returned from 69 laboratories in30 countries. The data were statistically analyzed and the results aredescribed in this report.The agreement between consensusmedian/mean and certified values was within uncertainty for all five samplesused in this IC exercise. Only small discrepancies existed among corelaboratories that reported close- to-consensus values and certified values.Normalized cumulative distributionsfor nitrate and phosphate obtained in 2018 were better (i.e., flatter) than thenormalized cumulative distributions obtained from previous IC exercisesconducted in 2008, 2012, and 2015. The indication is that comparability ofnitrate and phosphate analysis among the laboratories has gradually improvedfrom 2008 to 2018. In contrast with the nitrate and phosphate results, thenormalized cumulative distribution for silicate obtained in 2018 was similar tothe distributions in previous years. The indication is that comparability of silicateanalysis among the laboratories has not changed during these years.The results of this IC exercise alsoshowed that nonlinearity of the calibration curves for the nutrient analyses ineach laboratory is still a significant source of reduced comparability ofnutrient data. Analysis of ranked scatter plots led to this conclusion. Theimplication is that we need to use a set of nutrient CRMs, the concentrationsof which cover the whole range of nutrient concentrations in the world´s oceansto maintain comparability of results.Thirty-eight laboratories among 69used CRM/RM. The remaining 31 laboratories did not use a CRM/RM or did notreply to the questionnaire. It is obvious that the number of the laboratoriesthat use CRMs has been increasing since 2008. In general, the reported resultsfrom laboratories that used CRMs were located in the central part of the rankedplots and showed Z-scores, as expected. The results of this IC exercise implythat the majority of the participating laboratories are very capable ofmeasuring nutrient concentrations in seawater, and using CRMs will furtherincrease the comparability of results. The results may be SI traceable in thenear future.