Final report on CCQM-K91: Key comparison on pH of an unknown phthalate buffer

Results of the CCQM-K91 key comparison on pH of an unknown phthalate buffer with a nominal pH value of pH ~ 4.01 at 25 ?C are reported. Measurements are performed at 15 ?C, 25 ?C and 37 ?C and optional also at 5 ?C and 50 ?C. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).