Overview
SIST ISO 7875-2:1996 specifies an internationally recognized method for the determination of non-ionic surfactants in water using the Dragendorff reagent. This standard is part of the broader ISO 7875 series that addresses the analysis of surfactants critical to assessing water quality. It focuses on detecting trace amounts of non-ionic surfactants, particularly those composed of alkylphenol-alkylene oxide and alcohol-alkylene oxide adducts, commonly found in sewage influents and effluents, wastewaters, and surface waters.
The method centers on the air stripping of surfactants, their collection in ethyl acetate, and subsequent chemical analysis through precipitation and potentiometric titration. It includes detailed procedures to isolate surfactants and quantify them via their bismuth content, offering a reliable laboratory technique for environmental monitoring and wastewater management.
Key Topics
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Scope and Application
Applies to the measurement of low concentrations of bismuth-active substances correlated to non-ionic surfactants in aqueous samples. Suitable for influents, effluents, and potentially large-volume surface water samples to achieve detection limits as low as 0.05 mg/L.
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Principle of the Method
- Surfactants are stripped from the water sample using air or nitrogen.
- Collected in ethyl acetate and precipitated with Dragendorff reagent (a bismuth-based reagent).
- The precipitate undergoes dissolution, followed by titration with sodium pyrrolidin-1-yl dithiocarboxylate to determine bismuth concentration potentiometrically-a measure of non-ionic surfactants.
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Sample Handling and Preparation
Includes guidelines on sample volumes, handling suspended solids, and recommendations for preservation (e.g., cooling to 4 °C, use of formaldehyde or chloroform for storage). Emphasizes cleanliness and avoidance of contamination.
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Reagents and Apparatus
Specifies analytical-grade reagents like sodium chloride, sodium hydrogencarbonate, ethyl acetate, methanol, and bismuth oxynitrate. Apparatus includes gas-stripping equipment, ion exchange columns, and potentiometric titration devices with suitable electrodes.
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Interference and Separation
Details on removal of cationic surfactants, which can interfere by mimicking non-ionic types, using cation exchange resins. Anionic surfactants up to tenfold excess do not interfere significantly.
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Calculation and Reporting
Results are expressed in mg/L as an equivalent of nonyl phenol with 10 ethylene oxide units (NP10), encompassing the differences in surfactant chemical structures via an empirical factor. Instructions are provided for calculating concentrations and including relevant data in test reports.
Applications
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Wastewater Treatment Monitoring
Monitoring influents and effluents from sewage treatment plants to assess surfactant contamination levels, ensuring regulatory compliance and treatment efficacy.
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Surface Water Quality Assessment
Evaluating natural water bodies for pollution by synthetic cleaning agents containing non-ionic surfactants, which can affect aquatic ecosystems.
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Environmental Research
Conducting studies related to surfactant fate, transport, and biodegradability in aquatic environments.
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Industrial Effluent Testing
Screening wastewater discharges from manufacturing or cleaning industries using surfactant-rich products.
This method supports environmental protection agencies and laboratories in accurately quantifying surfactant pollution, essential for water pollution control, ecosystem health, and public safety.
Related Standards
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ISO 7875-1:1984 – Determination of anionic surfactants in water by the methylene blue spectrometric method. Complements Part 2 by addressing anionic surfactant analysis for a comprehensive surfactant profile.
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ISO 5667 Series
- Part 2: Guidance on sampling techniques for water quality.
- Part 3: Guidance on the preservation and handling of water samples.
These standards provide critical background for sampling accuracy, preserving sample integrity before analysis.
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ISO/TC 147 – Water Quality Technical Committee
The parent committee responsible for the development of ISO 7875, which addresses broader aspects of chemical testing and water quality standards.
Keywords: ISO 7875-2, non-ionic surfactants analysis, water quality testing, Dragendorff reagent method, surfactant determination, wastewater influent and effluent analysis, environmental monitoring, bismuth active substances, ion exchange resin, potentiometric titration, surfactant pollution detection.
