Comparison of primary measurement procedures for pH

Project Description

The purpose of this comparison is to assess the degree of equivalence of the national primary measurement procedures used to determine the pH of primary standard buffer solution. The measurement results obtained in the comparison will allow estimation of the capability of the participants to determine the pH of a phthalate buffer at different temperatures. The comparison is restricted to the use of hydrogen electrode/silver/silverchloride cells without liquid junctions (Harned cells). The pH determination are to be carried out at 15 °C, 25 °C and 37 °C. A batch of buffer solution will be produced by PTB. Each participant will receive three litre sample solution. The hydrochloric acid and the sodium chloride needed for the measurements will not be provided but individual laboratory material of stated high quality should be used. A description of the primary measurement method for pH has been described in the CCQM discussion paper on pH measurements (proceedings of the 6th CCQM meeting, BIPM 1999). The estimation of the measurement uncertainty must be conform to the ISO document: Guide to the expression of Uncertainty in Measurement (1993) 1st edn, ISO, Geneva. A suggestion for a summary table (Excel sheet)is given to the participants. The deadline for sending the results is the 15 April 2003. A draft report will be circulated for comment within one month after the deadline fixed for the receipt of the individual results.

The pH buffer solution of unknown composition used in this comparison resembles the sample used in  CCQM-K17. The measurement protocol is the same for both comparisons.

Final Report 2003-06-30

The comparison has been completed and the results are available in the KCDB.