Bromothymol Blue

25th October 2018



An image showing Bromothymol Blue in a 500ml container

Why Buy Bromothymol Blue Online from ReAgent Chemicals?

We supply bromothymol blue online in 5 kg and 25 kg containers. We also produce ready-made 0.04% bromothymol blue solutions. Discounts are available for bulk buying.

Weak Acid in Solution

Bromothymol blue, C27H28Br2O5S, is also known as bromthymol blue or bromothymol sulfone phthalein and is a popular pH indicator for weak acids and bases. Below pH 6 it remains yellow, changing to blue at pH above 7.6.

This means it’s commonly used to measure how neutral a solution is, or in other words, to measure around pH 7. For example, it’s used to measure the pH in fish tanks and swimming pools.

This compound behaves as a weak acid in solution, which can be both protonated and deprotonated, resulting in the yellow or blue solutions respectively. Around pH 7, it acquires a blue/green colouration. Bromothymol blue dissolves in water with difficulty, but it’s highly soluble in alcohol and ether or in alkaline solutions.


Taking advantage of its pH indicator properties, bromothymol blue has a few applications, including:

  • Studies in photosynthesis and respiration: This compound turns from green to yellow in the presence of CO2, as carbonic acid is formed.
  • Slide stain: A drop is added on top of the specimen to be analysed and the coverslip placed above. It can be used to mark cell walls or nuclei.
  • Obstetrics: Use to determine the premature rupture of membranes. As amniotic fluid has a pH higher than 7, bromothymol blue will turn blue if there’s fluid leaking from the amion. However, the test may be misleading, as it also turns blue in the presence of blood or infections.

Exceptional Customer Service

At ReAgent, we are very proud of our exceptional customer service. A member of staff will assist you before, during and after your purchase, as needed. To find out more about bromothymol blue or any other product, simply call us for a quote or technical question.


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