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Phenol red powder is an organic compound with the chemical formula C19H12O8S, CAS 143-74-8. It is a red crystalline powder, odorless, tasteless, insoluble in water, and soluble in organic solvents such as ethanol, acetone, chloroform, benzene, and alkaline solution. It is an acidic indicator that appears yellow under acidic conditions and red under alkaline conditions. It has a certain degree of oxidation-reduction ability and can be oxidized by oxidants or reduced by reducing agents. Phenol red indicators have various uses, including acid-base indicators, biological laboratory indicators, optical instrument cleaning agents, chemical synthesis intermediates, disinfectants and preservatives, laboratory extractants, ion exchangers, redox indicators, adsorbents, photometric determination of certain metals, pharmaceutical synthesis intermediates, and molecular biology research. These uses demonstrate the importance and application value of the phenol red pH indicator in different fields.
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Chemical Formula |
C19H14O5S |
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Exact Mass |
354.06 |
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Molecular Weight |
354.38 |
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m/z |
354.38, m/z: 354.06 (100.0%), 355.06 (20.5%), 356.05 (4.5%), 356.06 (2.0%), 356.06 (1.0%) |
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Elemental Analysis |
C, 64.40; H, 3.98; O, 22.57; S, 9.05 |
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Phenol Red, also known as phenolphthalein or sulfobromophthalein, is a triphenylmethane type organic reagent. Its appearance is a deep red crystalline powder that is soluble in ethanol, sodium hydroxide, and sodium carbonate solutions, slightly soluble in water, and insoluble in chloroform and ether. Phenol red has shown wide application value in various fields such as medical diagnosis, biological experiments, environmental monitoring, and industrial analysis due to its unique chemical properties and color change characteristics.
1.Renal function testing
Phenol red is a classic diagnostic reagent for renal function, and its monosodium salt form is used to detect renal tubular excretion function after intravenous injection. After injecting phenol red into the human body, more than 90% is excreted through the renal tubules. By measuring the time of appearance and total excretion of phenol red in urine, renal tubular function can be evaluated. For example, in normal adults, after intravenous injection of 0.1g phenol red, the excretion within 15 minutes should be ≥ 25%, and the total excretion within 2 hours should be ≥ 55%. This detection method is still a routine method for screening renal function abnormalities in primary medical institutions due to its simple operation and low cost.
2. Liver function test
Phenol red sodium salt can be used as a liver function test reagent and participate in quantitative analysis of serum bilirubin.
After binding with bilirubin, it forms a colored complex, and the absorbance is measured by spectrophotometry, which can indirectly reflect the metabolic capacity of the liver. In the improved Jendrassik Grof method, phenol red was used as a chromogenic reagent to increase the detection sensitivity to 0.1mg/dL.
3. Blood carbon dioxide measurement
Phenol red powder is a key reagent for blood gas analysis, used to determine arterial partial pressure of carbon dioxide (PaCO ₂). In the Van Slyke method, phenol red reacts with bicarbonate to form a red complex, and the PaCO ₂ value is quantified by color intensity, providing a basis for the diagnosis of respiratory failure, metabolic acidosis, and other diseases.
1.Cell culture monitoring
Phenol red is an essential pH indicator in cell culture media, with a color change range (pH 6.8-8.4) covering the physiological range of cell growth. Under neutral conditions, it appears red, while in acidic environments (such as metabolic acid production) it turns yellow, and in alkaline environments (such as abnormal CO ₂ concentration) it turns purple. For example, in breast cancer cell culture, the concentration of phenol red is usually controlled at 11mg/L, which can not only effectively indicate the pH change, but also avoid the potential impact of high concentration on cell proliferation. It is worth noting that phenol red has weak estrogenic activity and should be used carefully in the culture of hormone sensitive cells (such as MCF-7 breast cancer cells).
2. Microbial metabolism detection
Phenol red is a commonly used indicator for microbial culture media, which reflects the metabolic type of microorganisms through color changes. For example:
Screening of Urea Decomposing Bacteria: Decomposing urea to produce ammonia increases the pH of the culture medium, causing phenol red to turn from yellow to red. Identification of Proteus and Klebsiella.
Acid producing bacteria detection: Lactic acid bacteria ferment to produce lactic acid, and the culture medium is acidified. Phenol red changes from red to yellow and is used for quality control of yogurt fermentation agents.
Double sugar iron culture medium: a composite culture medium composed of phenol red, sodium thiosulfate, and lactose/glucose, used to identify intestinal bacteria through color changes (red → yellow) and gas production (H ₂ S black precipitate).
3. Enzyme assay
Phenol red can be used for detecting catalase activity. In the supernatant of macrophage culture, phenol red reacts with hydrogen peroxide under peroxidase catalysis to produce oxidized phenol red (yellow). The concentration of hydrogen peroxide can be quantified by measuring the absorbance at 600-610nm. This method has a sensitivity of 0.1 μ mol/L and is widely used in the evaluation of immune cell function.
Practical tools in the field of environmental monitoring
1. Water quality acidity and alkalinity testing
Phenol red is a portable reagent for rapid water quality detection, and its aqueous solution (0.04%) exhibits a yellow red gradient within the pH range of 6.8-8.4. For example, in river pollution monitoring, phenol red test strips can be used to determine the acidity and alkalinity of water bodies on site, assisting in determining whether industrial wastewater discharge exceeds the standard.
2. Soil acidity and alkalinity assessment
Phenol red can be used for rough determination of soil pH. Mix soil samples with phenol red solution and determine acidity or alkalinity through color changes: yellow (pH<6.8), orange (6.8-7.6), red (pH>7.6).
Although the accuracy of this method is not as good as pH meters, it is easy to operate and suitable for rapid screening in farmland.
3. Water pollution warning
Phenol red is sensitive to heavy metal ions such as Pb ² ⁺ and Cd ² ⁺, and can form colored complexes with certain metals. For example, in lead contaminated water, phenol red forms a red complex with Pb ² ⁺, and the absorbance is linearly related to the lead concentration, with a detection limit of 0.01mg/L, providing early warning for heavy metal pollution in water.
Innovative applications in the field of agricultural technology
1.Plant growth regulator
Phenol red powder has plant hormone like activity, which can promote seed germination and seedling growth. Research has shown that treatment with 0.1mmol/L phenol red can increase wheat seed germination rate by 15% and root length by 20%. Its mechanism of action may be related to regulating cell membrane permeability and enhancing antioxidant enzyme activity.
2. Pesticide residue detection
Phenol red is used for rapid screening of organophosphorus pesticides. In the acetylcholinesterase inhibition method, phenol red acts as a chromogenic reagent and reacts with iodothioacetylcholine to form a red complex.
Pesticide residues inhibit enzyme activity, resulting in a lighter color. The pesticide concentration can be quantified by colorimetric method, with a detection limit of 0.01mg/kg.
3. Fertilizer quality assessment
Phenol red is used to determine the water-soluble phosphorus content in compound fertilizers. In the molybdenum antimony colorimetric method, phenol red is used as a masking agent to eliminate the interference of iron and aluminum ions, making the color development of phosphorus molybdenum blue more stable and improving the measurement accuracy.
Potential value in the food industry sector
1. Food acidity regulation
Phenol red is used as a food grade pH indicator to monitor the acidity of fermented foods. For example, in yogurt production, phenol red can reflect the degree of lactic acid bacteria fermentation in real time, avoiding excessive acidification and quality decline.
2. Food additive testing
Phenol red is used to detect alkaline dyes illegally added to food. Some illegal vendors add Sudan Red to chili powder, and phenol red can undergo color reaction with Sudan Red. Through thin layer chromatography (TLC) separation and identification, it provides technical support for food safety supervision.
3. Beverage quality control
Phenol red is used for the determination of carbon dioxide content in carbonated beverages. In the pressure digestion method, phenol red reacts with bicarbonate to form a red complex, and the CO ₂ concentration is quantified by color depth to ensure consistency in beverage taste.
There are two common synthesis methods for Phenol Red Powder .
Method 1: Phenol Red Method
(1) Reaction principle
The phenol red method uses phenol as the raw material and generates phenol red by reacting with sulfuric acid and formaldehyde. The principle of reaction can be expressed as:
C6H5OH + HCHO + H2SO4 → C19H12O8S + H2O
(2) Reaction steps
① Mix phenol with formaldehyde and add an appropriate amount of sulfuric acid for reaction. At this point, phenol and formaldehyde undergo a condensation reaction under the action of sulfuric acid, producing the intermediate product hydroxymethylphenol.
② Control the reaction temperature and time to ensure that the reaction proceeds fully. At a certain temperature, hydroxymethylphenol undergoes sulfonation reaction with sulfuric acid to produce phenol sulfonic acid.
③ Slowly add formaldehyde solution while stirring. Formaldehyde undergoes condensation reaction with phenol sulfonic acid to produce phenol red.
④ After the reaction is complete, filter out the generated phenol red crystals and wash them with an appropriate amount of water. After washing, the crystals are dried to obtain phenol red products.
(3) Precautions
In the synthesis process of phenol red method, the following points need to be noted:
① Strictly control the reaction temperature and time to avoid the occurrence of side reactions.
② Ensure that the amount of sulfuric acid is appropriate to avoid the generation of excessive by-products.
③ When adding formaldehyde solution, it is necessary to ensure that the temperature and concentration of the solution are appropriate to avoid generating too many by-products.
Method 2: Catechol method
(1) Reaction principle
The catechol method uses catechol as the raw material and generates phenol red by reacting with sulfuric acid and formaldehyde. The principle of reaction can be expressed as:
C6H4(OH)2 + HCHO + H2SO4 → C19H12O8S + H2O
(2) Reaction steps
① Mix catechol with sulfuric acid and heat to a certain temperature. At this temperature, catechol undergoes sulfonation reaction with sulfuric acid to produce catechol sulfonic acid.
② Slowly add formaldehyde solution while stirring. Formaldehyde undergoes a condensation reaction with catechol sulfonic acid to produce phenol red.
③ Control the reaction temperature and time to ensure that the reaction proceeds fully. At a certain temperature, after the condensation reaction is completed, the generated phenol red will crystallize and precipitate.
④ After the reaction is complete, filter out the generated phenol red crystals and wash them with an appropriate amount of water. After washing, the crystals are dried to obtain Phenol Red Powder products.
(3) Precautions
In the synthesis process of catechol method, the following points need to be noted:
① Strictly control the reaction temperature and time to avoid the occurrence of side reactions.
② Ensure that the amount of sulfuric acid is appropriate to avoid the generation of excessive by-products.
③ When adding formaldehyde solution, it is necessary to ensure that the temperature and concentration of the solution are appropriate to avoid generating too many by-products. At the same time, slowly add formaldehyde solution to avoid the occurrence of local overheating caused by the instantaneous generation of a large amount of heat During the crystallization process, it is necessary to control the crystallization temperature and time to obtain high-quality phenol red crystals. At the same time, it is necessary to prevent the occurrence of crystal decomposition and deliquescence.
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