BROMOCRESOL GREEN: CHARACTERISTICS, PREPARATION, USES - BIOLOGY - 2024

The bromocresol green is an organic dye belonging to the family of triphenylmethane. Its scientific name is 3,3 ', 5,5'-tetrabromo m-cresolsulfonphthalein. Its chemical formula is C ₂₁ H ₁₄ Br ₄ O ₅ S. This substance meets the characteristics and properties of a pH indicator. For this reason it is used for this purpose.

It has the ability to react to change in pH in the range 3.8 to 5.4, where it changes from yellow to blue-green. The bromocresol green pH indicator is synthesized from the addition of various bromine molecules to purple cresol; process known as bromination.

Structure of bromocresol green and spectrum of colors according to pH. Source: top image: en.wikipedia.org/wiki/User:Nevermore78 Nevermore78] -Permission = free -other_versions =}} / Bottom image: Natan Consigli.

It is used as a pH indicator for volumetric analysis in chemistry laboratories. It is also useful for coloring the running front in the separation of proteins and DNA in the agarose gel electrophoresis technique. Likewise, bromocresol green is used in the thin-layer chromatography technique.

Finally, it is important to note that this substance should not come into direct contact with skin and mucous membranes, as it is an irritant substance. It can also generate toxic fumes in the event of fires.

characteristics

Bromocresol green occurs as a greenish-brown crystalline solid. It has a molecular mass of 698.04 g / mol, a melting point between 217-218 ° C and its density is 0.979 kg / L. Bromocresol green decomposes at 225 ° C.

It is slightly soluble in water, moderately soluble in benzene, and soluble in ethanol, diethyl ether, ethyl acetate, and NaOH.

On the other hand, the bromocresol green pH indicator has an isosbestic point at 515 nm. This means that at that wavelength the substance maintains its absorbance, regardless of the pH in which it is found.

Preparation

Bromocresol Green 0.01%

Weigh 0.10 g of bromocresol green and dissolve in 7.2 ml of 0.020 M NaOH. Make up to 250 ml with distilled water.

It should be stored at room temperature, in a well ventilated place.

Bromocresol Green 0.04%

Weigh 40 mg of bromocresol green and dissolve in 17 ml of absolute ethanol and 0.58 ml of 0.1 mol / L NaOH. Make up the volume with distilled water up to 100 ml.

Applications

Chemical Substance Assessment

It is used in chemistry laboratories as a pH indicator for volumetric analysis.

Agarose gel electrophoresis

Bromocresol green has been used to color the running front in the separation of proteins and DNA in the agarose gel electrophoresis technique.

Thin layer chromatography

This technique is used for the separation of complex mixtures.

Bromocresol green is used as a developer, especially for substances that contain carboxylic acids and sulfonic acids or also to separate substances that have a pKa below 5.

Determination of deoxyribonucleic acids (DNA)

Chen et al. Described a technique for detecting DNA using bromocresol green and a common spectrofluorometer to measure the intensity of scattering of resonance light. They got good results.

Optical biosensors

A biosensor is an electronic device to which a telltale substance has been attached. This, when reacting with a certain biological substance, converts the biochemical signal into an electrical signal that can be measurable.

There are optical biosensors to which bromocresol green has been attached for the determination of serum albumin. The biosensor has a detector cell that captures the absorption of light at a wavelength of 630 nm.

The reaction detects the color change from yellow to green when bromocresol green binds to serum albumin at a pH of 3.8.

Toxicity

Health risks

Different international organizations consider bromocresol green as a product with a health risk 2. This means that it presents a moderate risk. Regarding flammability and reactivity, it is classified with a 1 and a 0 respectively; that is, there is a slight risk of flammability and there is no risk of reactivity.

Depending on the type of exposure with the compound, certain health problems can occur. Among them are the following: inhalation of vapors, direct contact with skin and mucous membranes, among others.

In this sense, the inhalation of vapors produces inflammation in the respiratory tract. If there is contact with the skin, irritation occurs in the affected area.

Eye contact can cause irritation of the ocular mucosa, and if absorbed it can cause nausea, vomiting, headaches, vertigo and drunkenness.

In case of fires it is important to know that bromocresol green can generate some toxic vapors, such as hydrogen bromide and sulfoxides.

First aid

Wash the affected area with plenty of water for 15 minutes in case of contact with the skin. If the substance has splashed on the ocular mucosa, it should be washed with plenty of water with the eyes open.

As an adjunct treatment, an emollient cream can be used on the affected skin to relieve irritation. If irritation persists, see a dermatologist.

In case of inhalation, move the patient to an airy place; and if there are signs of suffocation, give assisted breathing.

Incompatibility with other substances

Bromocresol green cannot be close to the following substances, as they are incompatible:

- Organic nitrogen compounds.

- Alkaline earth metals.

- Perchloric, chromosulfuric and nitric acids.

- Perchlorates.

- Halogenates.

- Chromium trioxide.

- Halogenoxides.

- Nitrogen and non-metallic oxides.

Impact on the environment

In case the substance is accidentally spilled, it must be collected mechanically with absorbent materials. Dispose of in an appropriate container. It should not be poured down the drain.

Although the effect of this substance on the environment and on human health is not known, it is recommended not to dump its waste directly on the ground, or into water sources without first having been treated.

In this sense, Guarín and Mera studied the effect of heterogeneous photocatalysis, using a titanium dioxide catalyst, together with a discontinuous reactor (Batch type), and under artificial UV radiation.

They obtained a high degradation and mineralization of the bromocresol green (84% and 82.5%) respectively. Therefore, these types of procedures are recommended for the treatment of liquid waste containing bromocresol green.

References

1. Guarín C, Mera A. Heterogeneous photocatalysis with TIO ₂ for the treatment of liquid waste with the presence of the green indicator of bromocresol. Engineering Magazine Universidad de Medellín. 2011; 10 (19): 79-88. Available at: web.archive.org.
2. "Bromocresol green." Wikipedia, The Free Encyclopedia. 16 May 2018, 14:07 UTC. 26 May 2019, 22:12. wikipedia.org
3. PanReac Appli Chem ITW Reagens. Bromocresol Green Safety Data Sheet. Available at: itwreagents.com/
4. "Thin layer chromatography." Wikipedia, The Free Encyclopedia. 28 Apr 2019, 11:21 UTC. 26 May 2019, 23:44 en.wikipedia.org.
5. Tianjin Red Cliff Chemical Reagent Factory. Bromocresol green. 2011.Available at: en.made-in-china.com
6. Favela Pro SA Products for laboratories and aquaculture. Bromocresol green. Available at: javeriana.edu.co/documents
7. Chen X, Cai C, Zeng J, Liao Y, Luo H. Study on bromocresol green-cetyltrimethylammonium-deoxyribonucleic acids system by resonance light scattering spectrum methods. Spectrochim Acta A Mol Biomol Spectrosc.2005; 61 (8): 1783-8. Available in: ncbi.nlm.nih.gov