Published in “The Spectrophotometric Calibration of pH electrodes in Seawater Using Purified m-Cresol Purple, Environmental Science and Technology by Dr Regina A. Easley and Dr. Robert H. Byrne.
This demonstrates the vast color variability of m-Cresol Purple.
Aquatic chemists use dyes rather than pH paper or often electrodes to measure pH because it is much more stable and reliable. Electrodes for measuring pH can drift easily and an environment with strong electromagnetic flux like a research vessel can easily throw all your measurements off. Even a crew member walking by with a walkie-talkie can destroy all your hours of calibration.
This paper demonstrated a method of performing these calibrations effectively with new purified MCP.
Easley, R.A., Byrne, R. H. (2012), Spectrophotometric Calibration of pH Electrodes in Seawater Using Purified m-Cresol Purple, Environ. Sci. Technol., 46(9): 5018-5024 doi: 10.1021/es300491s