Overview
ISO 11048:1995 - Soil quality: Determination of water‑soluble and acid‑soluble sulfate - specifies standardized laboratory procedures to extract and quantify sulfate from air‑dried soils and soil‑like materials. The standard defines preparation of water and dilute‑acid extracts and a gravimetric determination in which barium chloride is added to form barium sulfate (BaSO4), the precipitate is dried and weighed, and sulfate content is calculated from masses used.
Key topics and technical requirements
- Scope and applicability: Applicable to all types of air‑dried soils (agricultural, polluted site materials, etc.). Includes provisions on sample pretreatment.
- Sample preparation: Air‑drying, removal of >2 mm material where appropriate, subdividing (riffle or equivalent), and milling to required particle sizes (examples: pass 2 mm, mill to 250 μm for some tests). Test samples dried at ≤40 °C; dry‑matter determination follows ISO 11465 (≤75–80 °C).
- Extraction procedures:
- Water extractions at soil:water ratios of 1:5 and 1:2 (sections 3 and 4) with controlled agitation and filtration.
- Acid extraction using dilute hydrochloric acid (section 5) to determine acid‑soluble sulfate.
- Analytical method: Gravimetric precipitation with barium chloride (section 6) - precipitate BaSO4 dried and weighed. Method sensitivity is applicable to solution sulfate ≥10 mg/L.
- Performance limits: Minimum detectable concentrations in air‑dried soil for the gravimetric route are approximately 50 mg/kg (1:5 extraction), 20 mg/kg (1:2), and ~500 mg/kg for acid‑soluble sulfate. Practical maximum extractable amounts are also discussed (e.g., ~7 205 mg/kg for 1:5 extraction, ~2 882 mg/kg for 1:2).
- Limitations & interferences: Soils with gypsum, sulfides or multiple sulfur species, or high levels of competing ions may require special handling or alternative methods. The standard notes that other analytical techniques (ion chromatography, ICP/AES, titrimetry, turbidimetry) exist but are outside its scope.
- Precision and reporting: Includes precision information and recommended test report contents (section 7 and annexes).
Applications and users
ISO 11048 is used for:
- Routine soil testing in agricultural and environmental labs (sulfate availability and mobility).
- Pollution assessment and monitoring of former industrial sites (gasworks, collieries) where sulfur speciation matters.
- Construction and materials assessment, e.g., evaluating sulfate attack potential on concrete and building materials.
- Regulatory and research laboratories, agronomists, environmental consultants, and civil engineers requiring a validated sulfate determination protocol.
Related standards
- ISO 11464 - Pretreatment of samples for physico‑chemical analyses
- ISO 11465 - Dry matter and water content (gravimetric)
- ISO 3696 - Water for analytical laboratory use (purity grades)
- ISO 9280 - Sulfate determination (gravimetric using barium chloride)
Keywords: ISO 11048, soil quality, water‑soluble sulfate, acid‑soluble sulfate, gravimetric method, barium sulfate, soil testing, sulfate determination, soil analysis standards.
