Final report of key comparison CCQM - K105 'Electrolytic conductivity at 5.3 S⋅m^-1'

Abstract

The aim of key comparison CCQM-K105 was to demonstrate the measurement capabilities of the participating institutes with respect to the conductivity of multi-component aqueous salt solutions. Practical salinity results are currently not traceable to metrological references consistent with the International System of Units (SI). Nevertheless, salinity is one of the most important input quantities for oceanographic models, whose measurement data must be accurate on very long timescales. Thus, in order to determine the practical salinity value, there is a strong interest on the part of oceanographic researchers in establishing the traceability to the SI of conductivity measurements. To this end, the conductivity of a standard seawater sample, provided by the support laboratory (PTB), was measured in a way that was traceable to the SI. The nominal conductivity values of the solution were 5.3 S m-1 at 25 °C and 4.3 S m-1 at 15 °C. Thirteen institutes taking part in the comparison had to measure the conductivity values of the sample at both temperatures. The median was chosen for both values as an estimator for the KCRV, evaluated on the basis of the Monte Carlo method. An institute requested to be excluded from the determination of the KCRV because of contact problems of its cell. At 25 °C the KCRV is 5.3024 S m-1 with an interval of confidence (at the 95.45% level of significance) from 5.3005 S m-1 to 5.3044 S m-1. At 15 °C the KCRV is 4.2892 S m-1 with an interval of confidence (at the 95.45% level of significance) from 4.2877 S m-1 to 4.2907 S m-1. For the 'how far the light shines' statement the CMCs can cover the range 1 S m-1 to 15 S m-1 for the values 5.3 S m-1 at 25 °C and 4.3 S m-1 at 15 °C. This comparison is a follow-up of the CCQM Pilot Study P111. Main text. To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM.