NATIONAL BUREAU OF STANDARDS NOTES.
[J. P. I.
pH range, 7 to IO. Potassium p-phenolsulfonate is a good buffer for the pH range of 8. 4 to 9.2, and for spectrophotometric pH work with certain indicators. Since the purified product is not commercially available and since quantitative tests for indicating its purity have not been reported, an investigation covering the purification, assaying, and ultraviolet absorption spectra of potassium p-phenolsulfonate was undertaken by Elizabeth E. Sager, Marjorie R. Schooley, and S. F. Acree at the Bureau. Several recrystallizations from water of a commercial product gave a pure compound. A quantitative method of analysis by bromometric titration was developed, and it was found that two molecules of bromine react quantitatively with one molecule of p-phenolsulfonate in molar hydrochloric acid at o ยฐ C. within 5 minutes.
Ultraviolet absorption spectra were obtained for the impure compound and for the successive portions of the material su.bjected to six recrystallization steps. The spectrophotometric data agreed with the results of bromine analyses. The spectrophotometric curves obtained for the secondary salt of the p-phenolsulfonate are quite different from those for the primary salt. The absorption spectra of the compound in water and in diluted hydrochloric acid indicate that the sulfonate group is almost completely ionized.
The detailed report on this work will be published in the October Journal of Research.