**Determination of Volatile Phenols in Water – 4-Aminoantipyrine Spectrophotometric Method**
**Keywords**: Determination of volatile phenols in water; 4-aminoantipyrine spectrophotometry; US analytical instruments; UV-1100; UV-1200
Volatile phenols are organic compounds that can be distilled with water vapor, typically having boiling points below 230°C. They are mostly monohydric phenols and commonly found in industrial wastewater from processes like refining, gas washing, coking, papermaking, and chemical manufacturing. These substances are highly toxic and can cause acute poisoning if ingested in large amounts. Long-term exposure to even low concentrations (0.1–0.2 mg/L) may lead to symptoms such as dizziness, skin rashes, and nervous system disorders. High concentrations (>1 mg/L) can result in severe health issues or even death. Additionally, phenols in water can produce a fishy odor and chlorinated by-products that create unpleasant smells.
The 4-aminoantipyrine spectrophotometric method is widely used for the determination of volatile phenols. When the concentration exceeds 0.5 mg/L, the direct method is applied, while lower concentrations require extraction with chloroform for better accuracy.
For sample collection, glass containers are recommended. After collection, samples should be tested for oxidants. If present, excess ferrous sulfate is added, followed by phosphoric acid to adjust the pH to 4.0 using methyl orange as an indicator. A small amount of copper sulfate (1 g/L) is also added to prevent microbial oxidation. The samples must be stored at 5–10°C and analyzed within 24 hours.
Before analysis, pre-distillation is performed to remove color and turbidity. If interfering substances like oxidants, sulfides, or oils are present, they must be removed through appropriate pretreatment steps. For example, oxidants can be neutralized with ferrous sulfate, sulfides can be removed by adjusting pH and adding copper sulfate, and oils can be extracted using carbon tetrachloride.
In the 4-aminoantipyrine direct photometric method, phenolic compounds react with 4-aminoantipyrine in a basic medium (pH 10.00±0.2) in the presence of iron, forming a red indophenol dye. This compound absorbs maximally at 510 nm. The reaction is influenced by substituents on the phenol ring, with certain groups like nitro or hydroxy affecting the color development. The detection limit for phenol using a 20 mm cuvette is 0.1 mg/L.
Reagents required include a phenol standard stock solution, buffer solution (pH 10), 2% 4-aminoantipyrine solution, 8% iron solution, copper sulfate, phosphoric acid, and 5% ferrous sulfate. Calibration curves are prepared using different concentrations of phenol standards, and absorbance is measured at 510 nm. Blank samples are also analyzed to correct for background interference.
For the extraction method, the same reaction occurs, but the resulting dye is extracted into dichloromethane and measured at 460 nm. This method is suitable for drinking water, surface water, groundwater, and industrial wastewater. It has a lower detection limit (0.002 mg/L) and a higher upper limit (0.12 mg/L).
This method is efficient, accurate, and widely used in environmental monitoring. Proper handling of reagents and safety precautions, especially when working with organic solvents like ether, are essential. Always work in a fume hood and avoid open flames.
By following these procedures, laboratories can reliably determine the levels of volatile phenols in water samples, ensuring compliance with safety and environmental regulations.
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