ISO 6845:1989

Overview

ISO 6845:1989 specifies a laboratory procedure for the determination of the mean relative molecular mass of alkane monosulfonates and the alkane monosulfonate content in technical alkane sulfonates. The method is applicable to alkali metal salts produced by sulfochlorination and sulfoxidation of straight-chain paraffins (C12–C20) provided the sample does not contain significant paraffinic impurities. The procedure integrates solvent extraction, ion-exchange cleanup, neutralization and gravimetric determination to support surfactant analysis and quality control.

Key Topics

• Sample preparation: Test portion is dissolved in ethanol and acidified to convert salts to alkane monosulfonic acids.
• Liquid–liquid extraction: Alkane monosulfonic acids are separated from disulfonates and sulfate ions by extraction with light petroleum using a liquid–liquid extractor.
• Evaporation & redissolution: The petroleum phase is evaporated; the residue is dissolved in ethanol for further cleanup.
• Cation-exchange cleanup: Traces of alkali are removed by passage through a strongly acidic cation-exchange resin to avoid titration interferences.
• Neutralization & titration: Eluate is neutralized with carbonate-free sodium hydroxide and the sodium alkane monosulfonates are isolated.
• Gravimetric determination: The sodium alkane monosulfonates are dried under defined conditions and weighed to obtain mass for calculations.
• Calculations: From the mass and titration data the mean relative molecular mass (Mr) and the alkane monosulfonate content (% m/m) are calculated as specified.
• Precision data: Interlaboratory precision figures are provided in the standard (example: mean Mr ≈ 320 with reproducibility SD ≈ 6.49; mean monosulfonate content ≈ 16.92% with reproducibility SD ≈ 0.29).

Safety note: Volatile solvents and petroleum fractions must be evaporated in a well‑ventilated fume cupboard; follow local laboratory safety rules.

Applications

This ISO method is intended for laboratories and manufacturers performing:

• Quality control of technical alkane sulfonates and related surfactant products.
• Batch release testing to verify monosulfonate content and compositional consistency.
• Regulatory and compliance testing where a standardized, reproducible method is required.
• Research and development investigations into surfactant formulations derived from paraffins.

The procedure supports reliable surfactant analysis by combining solvent extraction, ion-exchange cleanup and gravimetric measurement to yield robust mass- and molar-based results.

Related Standards

• ISO 607 (Sample division for surface active agents and detergents) - for correct laboratory sampling.
• ISO 385-1 (Laboratory glassware - Burettes) - for volumetric apparatus quality.

Refer to the full ISO 6845:1989 text for detailed apparatus dimensions, reagent preparations, stepwise procedure, calculation formulae and test reporting requirements.