Bromothymol Blue - Uses

Uses

Bromothymol blue may be used for observing photosynthetic activities, or as a respiratory indicator (turns yellow as CO₂ is added). A common demonstration of BTB's pH indicator properties involves exhaling through a tube into a neutral solution of BTB. As carbon dioxide is absorbed from the breath into the solution, forming carbonic acid, the solution changes color from green to yellow. Thus, BTB is commonly used in middle school science classes to demonstrate that the more that muscles are used, the greater the CO₂ output.

It may also be used in the laboratory as a biological slide stain. At this point it is already blue, and a drop or two is used on a water slide. The cover slip is placed on top of the water droplet and the specimen in it, with the blue coloring mixed in. It is sometimes used to define cell walls or nuclei under the microscope.

Bromothymol is used in obstetrics for detecting premature rupture of membranes. Amniotic fluid typically has a pH > 7.2, bromothymol will therefore turn blue when brought in contact with fluid leaking from the amnion. As vaginal pH normally is acidic, the blue color indicates the presence of amniotic fluid. The test may be false-positive in the presence of other alkaline substances such as blood, semen, or in the presence of bacterial vaginosis.