ISO 6844:1983

Overview

ISO 6844:1983 specifies a titrimetric method for the determination of mineral sulfate content in surface active agents (surfactants). The procedure uses a buffered acetone medium and a standard volumetric lead(II) nitrate solution with dithizone as the end-point indicator. ISO 6844 is intended for anionic surfactants containing sodium, ammonium and alkanolamine sulfates and provides laboratory instructions, calculation formulae and precision data for routine quality control.

Key topics and requirements

• Principle: titration of a buffered acetonic solution of the test portion with a standard volumetric Pb(NO3)2 solution in the presence of dithizone; endpoint is a stable brick‑red color.
• Applicability: suitable for anionic surface active agents with sodium, ammonium or alkanolamine sulfates. Not applicable when interfering species are present (e.g., phosphates, large amounts of chloride, or large quantities of salts of weak acids such as soaps or monoesters of sulfosuccinic acid).
• Reagents and conditions: acetone solvent, dithizone indicator (0.5 g/L in acetone, store in dark), ammonium dichloroacetate buffer to control apparent pH (~4.1 ± 0.2 in acetone), and a prepared standard lead(II) nitrate solution. The method requires an acetone content of about 70–85% (V/V) in the final titration mixture.
• Procedure overview: prepare a laboratory sample, dissolve and dilute the test portion, take an aliquot, add dithizone, adjust apparent pH (NaOH / HNO3), add buffer and acetone, then titrate with lead(II) nitrate until the stable brick‑red endpoint is reached (stable for ~15 s).
• Results and precision: the standard provides the calculation for percent sodium sulfate and reports inter‑laboratory precision data (examples for low and moderate sulfate contents with given repeatability and reproducibility statistics).

Applications and users

• Quality control laboratories in detergent and surfactant manufacturing for routine sulfate determination.
• Raw material inspection and incoming goods testing where quantifying mineral sulfate content is required.
• Regulatory and compliance testing where standardized, traceable methods are needed.
• Analytical chemistry labs specializing in volumetric analysis and titrimetric methods.

Related standards

• ISO 607 - Sample division for surface active agents and detergents
• ISO 1042 - One‑mark volumetric flasks
• ISO 648 / ISO 835‑2 - Pipettes
• ISO 385‑2 - Burettes

Follow ISO 6844:1983 exactly for reagent concentrations, buffer preparation and calculation inputs. This ensures accurate, reproducible mineral sulfate results for anionic surfactants.