Thymol blue

Thymol blue is a reversible pH indicator that responds to the pH of the solution through structural changes of protonation and deprotonation. Thymol blue is red (HI- form) under acidic conditions and blue (I2- form) under alkaline conditions. Quantitative detection is achieved through the absorption peak shift (435 nm/596 nm) of the UV-visible spectrum. Thymol blue selectively responds to pH changes, changing from red to yellow at pH 1.2-2.8 and from yellow to blue at pH 8.0-9.6. Thymol blue can be fixed in a silica gel matrix through sol-gel technology to form a solid-state sensor for in-situ pH measurement in the marine environment and acid-base monitoring in the biomedical field[1][2].