Overview
ISO 6439:1990 - "Water quality - Determination of phenol index - 4‑Aminoantipyrine spectrometric methods after distillation" specifies standardized laboratory procedures to determine the phenol index in waters. The methods apply to drinking water, surface water, brines (saline waters), domestic waters and industrial waters. After a preliminary distillation, sampled phenolic compounds are measured either by a direct colorimetric method (Method A) or by a chloroform extraction/concentration method (Method B) using the 4‑aminoantipyrine reaction and spectrometric measurement at ~510 nm. Results are reported as milligrams of phenol per litre (mg/L phenol).
Key topics and technical requirements
- Scope: Phenol index measurement in various water types after steam distillation.
- Two methods:
- Method A (Direct colorimetric): suitable for samples with >0.10 mg/L phenol in the aqueous phase (no chloroform extraction).
- Method B (Chloroform extraction): concentrates colored product into chloroform phase; extends measurement range down to about 0.002–0.10 mg/L (practical detection limits noted around 0.01 mg/L in practice).
- Chemical reaction: steam‑distillable phenolic compounds react with 4‑aminoantipyrine and potassium hexacyanoferrate(III) at pH ~10 to form a red antipyrine dye measured spectrometrically at ~510 nm.
- Sample preservation & interferences:
- Acidify and add copper(II) sulfate at sampling to inhibit biological degradation and prevent sulfide formation.
- Remove oxidizing agents (e.g., ascorbic acid addition), manage oils/tar and sulfur compounds, and consider amine or reducing‑agent interferences.
- Apparatus & reagents: all‑glass distillation setup, spectrometer (10–100 mm cell path), pH meter; use analytical‑grade reagents and specified standard phenol solutions.
- Expression of results: interpolate absorbance on a calibration graph and convert to mg/L phenol equivalent.
Practical applications
- Routine laboratory testing of water quality for environmental monitoring, wastewater treatment control, industrial effluent testing and compliance checks where a phenol index is required.
- Useful for laboratories needing an ISO‑referenced spectrometric procedure for phenol determination after distillation and for comparative studies of phenolic contamination in different water matrices.
Who uses this standard
- Environmental testing laboratories, municipal water laboratories, industrial process and effluent labs, research institutions and quality assurance teams responsible for phenol monitoring and water safety assessments.
Related standards
Keywords: ISO 6439:1990, phenol index, 4‑aminoantipyrine spectrometric methods, water quality, phenol determination, distillation, chloroform extraction, spectrophotometer, drinking water testing.
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