**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. They are typically monohydric phenols with boiling points below 230°C. These substances are commonly found in industrial wastewater from processes such as oil refining, gas washing, coal coking, papermaking, ammonia synthesis, and wood preservation. Their presence in water is a serious environmental concern due to their high toxicity.
Exposure to even low concentrations of phenols (0.1–0.2 mg/L) can cause an unpleasant fishy odor in water, while higher concentrations (>1 mg/L) may lead to acute poisoning. Long-term consumption of contaminated water can result in symptoms like dizziness, skin rashes, itching, and nervous system disorders. In agriculture, water with high phenol content is unsuitable for irrigation, as it can harm crops or reduce yields. Additionally, when chlorinated, trace amounts of phenols can produce a distinct chlorophenol smell.
The most widely used method for determining volatile phenols is the 4-aminoantipyrine spectrophotometric method. When the concentration is above 0.5 mg/L, the direct method is applied. For lower concentrations (<0.5 mg/L), the chloroform extraction method is preferred.
To collect water samples, glass containers are recommended. After collection, the sample should be checked 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 inhibit microbial oxidation. The sample should then be stored at 5–10°C and analyzed within 24 hours.
Before analysis, pre-distillation is performed to remove interferences such as color, turbidity, and other contaminants. If oxidants, sulfides, or oils are present, appropriate pretreatment steps must be taken. For example, oxidants can be neutralized with ferrous sulfate, sulfides can be removed by adjusting the 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 the presence of iron at a pH of 10.00 ± 0.2, forming an orange-red indophenol dye. This compound absorbs strongly at 510 nm. The minimum detectable concentration of phenol is 0.1 mg/L using a 20 mm pathlength cuvette.
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. All reagents should be stored properly, especially solid ones, which should be kept in desiccators.
The analytical procedure involves preparing a calibration curve using known concentrations of phenol, followed by measuring the absorbance of the water sample. The blank value is subtracted to correct for background interference. The final concentration is calculated using the regression equation derived from the calibration curve.
For cases where lower detection limits are needed, the 4-aminoantipyrine extraction spectrophotometric method is used. The dye formed during the reaction can be extracted into dichloromethane and measured at 460 nm. This method is suitable for analyzing drinking water, surface water, groundwater, and industrial wastewater, with a detection limit of 0.002 mg/L and an upper limit of 0.12 mg/L.
By following these procedures, laboratories can accurately determine the levels of volatile phenols in water samples, ensuring compliance with environmental and health standards.
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