Electrolytic conductivity in aqueous solutions is one of the most used electrochemical measurement techniques in industry - it is relatively simple, cheap, and robust and is performing with a low measurement uncertainty compared with most other analytical techniques.
Since electrolytic conductivity is a sensitive measure of amount of ions dissolved in the solution a limit value for conductivity is a clear and simple quality specification for purity of water in general but also for high purity water. The relevant measuring range is below 2 mS/m (0.05 to 20 µS/cm at 25 °C). The European Pharmacopoeia as well as the Japanese and United States have indeed specified the demand for purified water, highly purified water and water for injection for the pharmaceutical industry based on conductivity. Sectors that also use conductivity limits for water purity are electrical power production, food industry, electronic industry and analytical laboratories.
At these low levels it is not feasible to circulate water samples due to contamination. The main contamination is coming from carbon dioxide in ambient air. In Euramet 898 (2006-2007) a comparison based on using a transfer standard calibrated at each laboratory were performed with PTB and SP as participants. In iMERA project T2J10 a direct comparison made at SP with conductivity cells from PTB and DFM. The outcome was that further comparisons are needed in the range 5 µS/m - 200 µS/m (0.05 - 20 µS/cm).
The proposal is to use a new system built with a closed loop for contamination of ultrapure water at PTB. The contaminant will be pure KCI. All participants will come to PTB with their calibrated instruments (primary or secondary). The participant cell will be put in the loop with the PTB and the electrical conductivity will be measured. The range will be from 5 µS/m - 2000 µS/m (0.05 - 20 µS/cm) and the measurements will be performed at a temperature of 25 °
Final Report 2014-08-19
The comparison has been completed and results are published in the KCDB.