Letter
to
the
pH Controversy revisited Analytical Chemistry recently published a "Letter to the Editor" by W. F. Koch on the longstanding controversy regarding pH standardization in IUPAC Commission V.5 (1). In this letter, Koch replied to a news story on an IUPAC announcement (2). His invitation of comments has prompted us to supply the following additional information. We are well aware that the "compromise" IUPAC Recommendations 1985 (3) are metrologically and legally intolerable. They recommend two alternative, incompatible protocols for assigning standard pH values to buffer solutions, and they contain further serious metrological errors (4). In view of this situation, we have started the following activities toward new IUPAC recommendations. In 1995, Renate Naumann initiated an IUPAC Project, "Calibration Traceability of pH Measurement, Recommended Procedures and Definitions." In 1996, Naumann initiated an Interdivisionary Working Party (WP) on pH at the meeting of IUPAC Commission V.5 in order to definitely reach a decision on the 20-year-old pH controversy. In 1997, this WP was formally establlshed at the IUPAC General Assembly in Geneva. It consists of members of Commissions V.5 and 1.3 and of experts from outside IUPAC including the authors of this letter. A joint proposal entitled "Proposal: Work schedule for Working party on pH IUPAC Commission V 5" favoring the multiprimary standard protocol was submitted In 1996, Petra Spitzer organized the 126th PTB-Seminar 'Traceability of pH Measurement". The intention of this seminar was to give international experts on pH the opportunity to present their opinions. Friedrich G. K Baucke gave a critical analysis of the IUPAC Recommendations 1985 226 A
Editor
and presented the new principles for scientifically correct, metrologically and legally sound, and easily practicable new recommendations on pH (4,5). K. W. Pratt reported on NIST's viewpoint (6). A. K. Covington gave a paper entitled 'Towards a Unified pH Scale for the 21st Century"(7). The term "unified pH scale" is also used in the IUPAC announcement and the news story (3). We think that this term, as well as the story's title, "pH—still to be defined", are misleading because they suggest that the two incompatible protocols can be unified and that an entirely new pH concept is envisioned. As we have already proposed, what is urgently needed at present is a new, twopart document. The first part, replacing Recommendations 1985, should be based on the metrologically and legally correct principles of one pH definition (8) and the multiprimary standard protocol. It can speedily be prepared, since the multiprimary standard protocol has already been accepted by most countries. This is, for instance, shown by two recent EUROMET Programs (9 10) and a third on that is presently underway. In addition this work will not be delayed by an application of the Pitzer equations since this treatment yields no improvements of currently applied standard pH values (11) The second parr ,o bb drafted subsequentiv should extend the multiprimary standards protocol to solutions with high ionic strength and at temperatures above 50° C. Friedrich G. K. Baucke Schott Glas (Mainz, Germany) Petra Spitzer PTB (Braunschweig, Germany) Renate Naumann Merck (Darmstadt, Germany)
Analytical Chemistry News & Features, April 1, 1998
(1) Koch, W. F. Anal. Chem., 1997, 69, 700 A. (2) Anal. Chem., 1197, 69, 521 A. (3) Covington, A. K.; Bates, R. G.; Durst, R. A. Pure Appl. Chem. 1985, 57, 531-42. (4) Baucke, F.G.K., in Traceability ofpH Measurementt PTB Bericht W-68, P. Spitzer, Ed.; PTB: Braunschweig, 1997; pp. .0-20. (5) Naumann, R.; Baucke, F.G.K., Spiizer, P. ibid, pp. .8-56. (6) Pratt, K. W. .bid, pp. 28-37. (7) Covington, A K.; Caraoes, M. F.. Ferra, M. I. ibid, pp. 21-27. (8) Sorensen, S.P.L; Linderstrom-Lang, K. Compt. Rend. Lab. Carlsberg b924,15, 6, 1-40. (9) Spitzer, P. Metrologia a196,33,95-96. (10) Spitzer, P. Metrologia 1997,34,375-76. (11) Covington, A K.; Ferra, M. A J. Soll Chem.. 1 9 9 4 , 2 3 , 1 .
Letters to the Editor We welcome your comments regarding published articles or other topics of interest to analytical chemists. Letters may be submitted by e-mail (
[email protected]), fax (202-872-4574), or regular
mail (Analytical Chemistry, ACS, 1155 16th S t , N.W., Washington, DC 20036). Please include your full address, signature, and daytime phone number. Letters should be brief and may be edited for clarity or space.
