3:30 PM - 3:45 PM
[AOS17-01] A new SI traceable silicon standard solution for certification of nutrients CRM and measurement of silicate in seawater, part two
Keywords:silicon standard solution, seawater, silicon, SI traceable, certified reference material
A new SI traceable silicon standard solution for certification of nutrients CRM and measurement of silicate in seawater was established (A-OS27-02, JpGU, 14th July 2020). This standard solution was produced by a dissolution technique with an alkaline solution and a silicon standard solution having a mass fraction of 1000 mg Si kg-1 was prepared. In June 2019 we produced 300 bottles of exp64 solution and a nominal mass fraction of solution prepared in June 2019 was 999.3 mg Si kg-1 and the certified mass fraction of this solution was 999.3 mg Si kg-1 ±2.8 mg Si kg-1 by a technology consulting system of AIST. In January 2021 we also produced 998 bottles of exp94 solution and the certified mass fraction of exp94 will be given by a technology consulting system of AIST in February 2021 again. The expanded uncertainty was 0.3 % for exp64 and this was better than the 0.5 % of NIST and Merck silicon standard solutions.
As a standard solution, homogeneity and long term stability are also essential. The homogeneity measurement result of the exp64 solution was 0.08 % in August 2019 and that of the exp94 solution was 0.07 % in January 2021. It is presumed that the long term stability might be theoretically good for a long period from a view of the chemical composition. No significant change in silicate concentration has been observed in the results of comparison between exp64 solution and certified reference materials of nutrients of lot CF of KANSO and NMIJ 7603-a.Long term storage experiment will be started soon. A small problem on production by the dissolution technique with an alkaline solution was found during our production experiments. We expected that silicon dioxide of which purity is 99.999 % should be reacted with sodium carbonate and a reaction rate of this might be very close to 100 %, however, measured silicate mass fraction showed that a reaction rate ranged from 99.29 % to 99.92 %. We need to seek the reasons for a little bit low reaction rate. We also did density measurements as a part of quality control of the production of this new silicon standard solution because we found a negative relationship between reaction rate and total mass after reaction by a dissolution technique with an alkaline solution.
This SI traceable silicon standard solution is already used to certify of nutrient CRM and is used to measure silicate concentration in seawater on the cruises of JAMSTEC worldwide. This new silicon standard solution will be provided to the coming ”IOCCP-JAMSTEC Inter-laboratory Comparison Exercise of a Certified Reference Material (CRM) for Nutrients in Seawater”, too.
As a standard solution, homogeneity and long term stability are also essential. The homogeneity measurement result of the exp64 solution was 0.08 % in August 2019 and that of the exp94 solution was 0.07 % in January 2021. It is presumed that the long term stability might be theoretically good for a long period from a view of the chemical composition. No significant change in silicate concentration has been observed in the results of comparison between exp64 solution and certified reference materials of nutrients of lot CF of KANSO and NMIJ 7603-a.Long term storage experiment will be started soon. A small problem on production by the dissolution technique with an alkaline solution was found during our production experiments. We expected that silicon dioxide of which purity is 99.999 % should be reacted with sodium carbonate and a reaction rate of this might be very close to 100 %, however, measured silicate mass fraction showed that a reaction rate ranged from 99.29 % to 99.92 %. We need to seek the reasons for a little bit low reaction rate. We also did density measurements as a part of quality control of the production of this new silicon standard solution because we found a negative relationship between reaction rate and total mass after reaction by a dissolution technique with an alkaline solution.
This SI traceable silicon standard solution is already used to certify of nutrient CRM and is used to measure silicate concentration in seawater on the cruises of JAMSTEC worldwide. This new silicon standard solution will be provided to the coming ”IOCCP-JAMSTEC Inter-laboratory Comparison Exercise of a Certified Reference Material (CRM) for Nutrients in Seawater”, too.