Bromothymol blue (also known as bromothymol sulfone phthalein and BTB ) is a pH indicator. It's mostly used in applications that require measurement of substances that will have a relatively neutral pH (close to 7). A common use is to measure the presence of carbonic acid in liquids. Usually sold in solid form such as sodium salt from acid indicator.
Video Bromothymol blue
Structure and properties
Bromothymol blue acts as a weak acid in solution. Thus it can be in protonated or deprotonated form, appear yellow or blue, respectively. It is a bright aquamarine by itself, and a turquoise blue in neutral solution. Neutral form prototon produces highly conjugated structures, explaining color differences. An intermediary of the deprotonation mechanism is responsible for the greenish color in neutral solutions.
The protonated bromothymol blue form has a peak absorption at 427 nm to emit yellow light in acidic solutions, and the deprotonation form has a peak absorption at 602 nm to emit blue light in a more basic solution.
The common blue carbon bromothymol framework is common to many indicators including red chlorophenol, blue thymol, and green bromocresol.
The presence of a moderate group of electrons (bromine atoms) and two moderate donor groups (alkyl substituents) is responsible for the active indication of bromothymol blue from pH 6.0 to 7.6. While conjugations are responsible for the length and nature of the color change ranges, these substituent groups are ultimately responsible for the active range of the indicator.
Bromothymol blue is slightly soluble in oil, but soluble in water, ether, and aqueous alkaline solution. It is less soluble in nonpolar solvents such as benzene, toluene, and xylene, and practically insoluble in petroleum ether.
Maps Bromothymol blue
Getting Started
To prepare the solution for use as a pH indicator, dissolve 0.10 g in 8.0 cm 3 N/50 NaOH and dilute with water up to 250 cm 3 . To prepare the solution for use as an indicator in volumetric work, dissolve 0.1 g in 100 º cm 3 50% (v/v) ethanol.
Usage
Bromothymol blue can be used to observe photosynthetic activity, or as a respiratory indicator (yellow as CO 2 is added). The general demonstration of the BTB pH indicator property involves blowing through the tube into the BTB neutral solution. When carbon dioxide is absorbed from the breath into the solution, forming carbonic acid, the solution changes color from green to yellow. Thus, BTB is usually used in science classes to show that the more muscles used, the greater the CO 2 output.
Bromothymol blue has been used in conjunction with red phenols to monitor the activity of the asparaginase fungus enzymes with red pink and blue blue bromothymol turning blue phenols showing elevated pH and enzyme activity. However, a recent study shows that methyl red is more useful in determining activity because of the form of bright yellow rings in the zone of enzyme activity.
It can also be used in the lab as a biological slide stain. At this point, it is blue, and a few drops are used on the water slide. The slip cover is placed over the water droplets and specimens inside, with mixed blue dye. Sometimes it is used to determine the cell wall or core under a microscope.
Bromothymol is used in obstetrics to detect premature rupture of the membranes. The amniotic fluid usually has a pH & gt; 7.2, bromothymol will therefore become blue when in contact with fluid leaking from the amnion. Because the vaginal pH is usually acidic, blue color indicates the presence of amniotic fluid. This test may be false-positive in the presence of other alkaline substances such as blood or semen, or in the presence of bacterial vaginosis.
See also
- pH indicator
- Litmus
- Fenolftalein
- Methyl orange
- Universal indicator
References
External links
- J.T.Baker MSDS
- Bromothymol Blue (Sodium Salt) -Sigma Aldrich
Source of the article : Wikipedia
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