Overview
EN ISO 23157:2022 (ISO 23157:2021) specifies a laboratory procedure for the determination of the silanol group content on the surface of fumed silica (pyrogenic silicon dioxide) using a reaction gas chromatographic method. Adopted by CEN from ISO, this standard provides a validated, reproducible route to quantify surface silanol groups - a key surface-chemistry parameter that affects dispersion, reactivity and performance of fumed silica in downstream applications.
Key Topics and Requirements
- Scope: Measurement of silanol groups on fumed silica by reaction gas chromatography (headspace GC of reaction-generated methane).
- Principle: Chemical reaction of surface silanol groups to generate a measurable gaseous product, analyzed by gas chromatography.
- Reagents and chemicals: Includes use of solvents (e.g., toluene), a Grignard reagent and calibration substances as specified in the method.
- Apparatus: Requirements cover a gas chromatograph with headspace system, oven, capillary column, sample vials, analytical balance and gas collection accessories.
- Sample pre-treatment: Procedures for drying and determining volatile matter (e.g., matter volatile at 105 °C) prior to reaction.
- Reaction and analysis: Detailed steps for conducting the reaction, headspace conditions, GC conditions, identification and calibration.
- Calculations and expression of results: Formulas to convert measured methane to surface silanol content and to correct for volatile components.
- Precision and quality: The document includes precision data, repeatability and reproducibility guidance, and annexes with representative chromatograms and precision information.
- Normative context: Prepared by ISO/TC 256 and adopted by CEN/TC 298; the EN version is identical to ISO 23157:2021.
Applications and Who Uses It
- Product manufacturers: Fumed silica producers use the method for product characterization and quality control.
- R&D and surface modification: Laboratories developing surface-treated silica for improved compatibility (silicone rubber, coatings, adhesives, sealants) rely on accurate silanol quantification.
- Quality assurance/testing labs: Ensures consistency between batches and supports specification compliance for pigments and extenders.
- Regulatory and procurement: Enables clear communication of material surface properties between suppliers and end-users.
Practical benefits include higher sensitivity and better reproducibility compared with some alternative approaches, making this method preferred where precise surface silanol data are required.
Related Standards
- Alternative analytical approaches mentioned in the standard include titration, thermogravimetry (TG) and infrared spectroscopy (IR) for silanol assessment. EN ISO 23157:2022 provides the gas chromatographic route as a standardized, high-sensitivity option.
