Spectrophotometric pH measurement in estuaries using thymol blue and m-cresol purple |
| |
| Authors: | Luke M Mosley Shamus LG Husheer Keith A Hunter |
| |
| Institution: | Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand |
| |
| Abstract: | The conditional acid dissociation constants (pKa′) of two sulfonephthalein dyes, thymol blue (TB) and m-cresol purple (mCP), were assessed throughout the estuarine salinity range (0<S<40) using a tris/tris–HCl buffer and spectrophotometric measurement. The salinity dependence of the pKa′ of both dyes was fitted to the equations (25 °C, total proton pH scale, mol kg soln−1):The estimated accuracy of pH measurements using these calculated pKa′ values is considered to be comparable to that possible with careful use of a glass electrode (±0.01 pH unit) but spectrophotometric measurements in an estuary have the significant advantage that it is not necessary to calibrate an electrode at different salinities. pH was measured in an estuary over a tidal cycle with a precision of ±0.0005 pH unit at high (S>30) salinity, and ±0.002 pH unit at low (S<5) salinity. The pH increased rapidly in the lower salinity ranges (0<S<15) but less rapidly at higher salinities. |
| |
| Keywords: | pH pKa Estuaries Absorption spectroscopy Sulfonephthalein indicators |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
