CCQM-P111 study on traceable determination of practical salinity and mass fraction of major seawater components

The first part of the study assessed the equivalence of practical salinity measurement results of a slightly diluted seawater sample from the North Atlantic, which were traceable to the SI. The study shows that the practical salinity reference value S _RV (here S _RV = 34.967) can be determined with a relative standard uncertainty of 3×10⁻⁴. This quantifies the uncertainty range, in which long-term comparability of practical salinity measurement results can be guaranteed currently. In the second part of the study, eight laboratories determined the mass fractions of five seawater components to quantify the equivalence of these measurement results. The results were: Na⁺ (10.726 ± 0.134) g/kg, Mg²⁺ (1.288 ± 0.018) g/kg, Sr²⁺ (0.00755 ± 0.00011) g/kg, Cl⁻ (19.360 ± 0.047) g/kg, SO₄ ²⁻ (2.650 ± 0.025) g/kg. The investigation confirmed the reference composition mass fractions of sodium, magnesium and chloride ions, but it showed a disagreement for strontium and sulphate ions.