Thymol Blue (sodium)

Thymol Blue sodium is an acid-base indicator used to indicate changes in pH. Thymol Blue sodium fades from red to yellow at pH 1.2 to 2.8 and from yellow to blue at pH 8.0 to 9.6. Quantitative detection is achieved through the absorption peak shift (435 nm/596 nm) of the UV-visible spectrum. Thymol blue sodium 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]. In Vitro:Guide (The following is our recommended experimental protocol. This protocol is for reference only and should be modified according to your specific needs).
Thymol Blue acid-base indicator protocol (solution state)^[1]:
1. Solution preparation
Dissolve Thymol Blue sodium salt in ethanol (or water/ethanol mixed solvent) to prepare a 0.1% (w/v) stock solution.
2. pH response test
Take the solution to be tested and add 1-2 drops of Thymol Blue indicator:
Acidic conditions (pH<1.7) The solution turns red (HI^- form).
Neutral to weakly alkaline (1.7≤pH≤8.9: the solution is yellow (intermediate state.
Strongly alkaline (pH>8.9): the solution is blue (I^2- form).
3. Quantitative detection
Use a spectrophotometer to measure the absorbance at 435 nm (HI^-) and 596 nm (I^2-), calculate the ratio R=A₅₉₆/A₄₃₅, and calculate the pH value using the ionization formula.