Bromothymol Blue is a pH indicator used for measuring pH around 7 in pools and fish tanks. It operates in the pH range 6.0 to 7.6 due to the presence of an electron withdrawing and donating groups like bromine atoms and alkyl substitutents respectively. In the laboratory, it is used as a biological slide stain as well as used in obstetrics for detecting premature rupture of membranes. Further, it is used for the observation of photosynthetic activities and a respiratory indicator. In addition to this, it is used to define cell walls or nuclei under the microscope.

This Thermo Scientific Chemicals brand product was originally part of the Alfa Aesar product portfolio. Some documentation and label information may refer to the legacy brand. The original Alfa Aesar product / item code or SKU reference has not changed as a part of the brand transition to Thermo Scientific Chemicals.