Overview
ISO 10084:1992 specifies a gravimetric method for the determination of mineral‑acid‑soluble sulfate content in solid fertilizers. The method is designed for fertilizers with sulfate contents, expressed as SO3, in the range 3% to 50% (dm). It defines the analytical principle, required reagents, apparatus, sample preparation references and calculation and reporting rules for routine laboratory determination.
Key topics and technical requirements
- Analytical principle: dissolve acid‑soluble sulfates in hydrochloric acid, precipitate sulfate as barium sulfate (BaSO4) using barium chloride, filter, wash, dry, ignite and weigh the precipitate (gravimetric determination).
- Reagents: analytical‑grade reagents including hydrochloric acid, barium chloride dihydrate (c = 122 g/l), and silver nitrate solution for chloride testing.
- Apparatus: common laboratory equipment supplemented by:
- electric hot‑plate,
- filter crucibles with porcelain disc (porosity grade P10),
- ovens capable of 120 °C and 800 °C,
- desiccator.
- Sample preparation: prepare laboratory sample according to ISO 8358 and take an adequate test portion so the SO3 in the test portion is 200–600 mg (select test portion mass per clause/table guidance).
- Procedure highlights: boiling in HCl, dilution and filtration, controlled precipitation at ~60 °C with BaCl2, thorough washing to remove chlorides (verified with AgNO3), drying at 120 °C, ignition at 800 °C, and weighing to 0.1 mg.
- Calculation: mineral‑acid‑soluble sulfate as SO3 is calculated using:
Ws = 85.75 × m1 / m0
where m1 = mass of dried/ignited BaSO4 precipitate (g) and m0 = mass of test portion (g). Results are rounded to 0.01% (dm).
- Precision: method precision established by inter‑laboratory studies (ISO 5725). Repeatability and reproducibility limits are defined by formulae in the standard:
- r = 0.042% + 0.0091 × Es (repeatability)
- R = 0.098% + 0.0284 × Ws (reproducibility)
Applications and users
- Quality control and production testing in fertilizer manufacturing.
- Regulatory compliance testing where official sulfate content certification is required.
- Analytical and contract laboratories performing routine fertilizer chemical analysis.
- Agronomists and R&D groups verifying sulfate supply in soil conditioners and fertilizer blends.
- Standardization bodies and proficiency testing organizers using validated gravimetric procedures.
Related standards
- ISO 8358 - Preparation of samples for chemical and physical analysis of solid fertilizers (sample splitting and lab sample).
- ISO 5725 - Precision of test methods (used to establish repeatability and reproducibility).
Keywords: ISO 10084:1992, solid fertilizers, mineral‑acid‑soluble sulfate, gravimetric method, sulfate determination, BaSO4 precipitation, fertilizer analysis, ISO 8358, ISO 5725.