Overview
ISO 8215:1985 specifies a gravimetric method for the determination of total silica content in commercial washing powders (detergents and surface-active agents). The procedure removes ethanol‑soluble material, isolates the ethanol‑insoluble fraction, digests with hydrochloric acid, and determines silica gravimetrically by ignition and weighing. The method applies to all types of washing powders except those containing acid‑insoluble materials other than silica.
Keywords: ISO 8215, washing powders, total silica, gravimetric method, silica content determination, detergent analysis, surface active agents.
Key topics and requirements
- Scope: Intended for commercial washing powders; excludes products with other acid‑insoluble matter.
- Sample size and precision: Typical test portion ~10 g (weighing accuracy 0.01 g). Reported repeatability ~0.15% and reproducibility ~0.29% for samples with ~3–7% silica.
- Main principle: Remove ethanol‑soluble organics (Soxhlet or beaker extraction), treat ethanol‑insoluble residue with hydrochloric acid and evaporate to dryness, repeat acid treatment twice, filter precipitate, and ignite to constant mass.
- Reagents: analytically pure reagents; ethanol (anhydrous/denatured), hydrochloric acid (density ~1.16–1.19 g/ml), silver nitrate solution for chloride endpoint, distilled or equivalent water, pumice as boiling regulator.
- Apparatus and conditions:
- Soxhlet extractor (500 ml flask, 200 ml extractor tube) or beaker extraction alternative.
- Porcelain filtering crucible (porosity P1–P4) or ashless filter; platinum crucible for ignition.
- Oven at 105 ± 2 °C for drying; electric furnace adjustable 900–960 °C for ignition (final ignition typically at 900 °C).
- Typical Soxhlet extraction: rapid extraction for about 2 h 30 min after first siphon.
- Calculation: Silica content expressed as mass percent = (mass of silica residue / mass of test portion) × 100.
Applications
- Quality control in detergent and washing‑powder manufacturing to monitor silica levels (fillers, anti‑caking agents).
- Regulatory compliance and product labeling where silica content is specified.
- Laboratory analysis in testing and inspection labs performing surfactant and detergent composition analyses.
- Useful for formulation development, failure investigations, and supplier verification.
Related standards
- ISO 607 - Sampling and division methods for surfactants and detergents (referenced for sample preparation).
- Laboratories should follow good analytical practice and consult current ISO editions for updates or replacements of ISO 8215:1985.
This summary helps analysts and quality managers quickly understand ISO 8215’s scope, procedure essentials, equipment/reagent needs, and practical uses for detergent silica determination.