Overview
ISO 20702:2017 - "Fertilizers and soil conditioners - Determination of microamounts of inorganic anions in fertilizers by ion chromatography" - specifies a validated analytical method to determine trace, water‑soluble inorganic anions in fertilizers and soil conditioners. The standard targets six anions: fluoride (F−), chloride (Cl−), bromide (Br−), iodide (I−), nitrite (NO2−) and thiocyanate (SCN−) using ion chromatography (IC) with suppressed conductivity detection. It provides requirements for sample preparation, reagents, instrumentation and reporting to ensure reliable, high‑throughput screening of microamounts in fertilizer matrices.
Key technical topics and requirements
- Scope: Determination of microamounts of water‑soluble inorganic anions in fertilizers (ISO 20702:2017).
- Analytical principle: Extraction by sonication, centrifugation and clean‑up (SPE‑C18, Ba‑ion and Ag/H filter columns), 0.22 μm filtration, separation by ion‑exchange chromatography and measurement by suppressed conductivity detector; quantitation via calibration curves.
- Sample preparation:
- Grind sample to pass 0.5 mm sieve; prepare 1–2 g test portions in 100 ml.
- Sonicate 30 min, centrifuge (≈4 000 r/min for 5–10 min), filter and pass through activated SPE and ion filter columns.
- Reagents and eluents:
- Potassium hydroxide eluent for gradient IC; carbonate/acetone eluent for isocratic IC.
- Stock solutions and anion working standards covering typical calibration ranges (0.2–20 mg/l per anion).
- Safety note: acetone and methanol are flammable/toxic - use fume hood and SDS guidance.
- Apparatus: Ion chromatograph with conductivity detector, ultrasonic cleaner, centrifuge, syringe‑driven 0.22 μm filters, SPE‑C18, Ba‑ion and Ag/H filter columns.
- Quality and precision: Method includes procedures for calibration, duplicate measurements, ring test evaluation and reporting of repeatability (r) and reproducibility (R).
Practical applications and users
ISO 20702:2017 is intended for:
- Analytical and environmental laboratories performing fertilizer quality control.
- Fertilizer and soil conditioner manufacturers for product compliance and specification control.
- Regulatory bodies and certification agencies monitoring contaminant levels in fertilizers.
- Soil scientists and agronomists assessing potential adverse effects from inorganic anions on crops and soil health.
Benefits include rapid, high‑throughput determination of trace anions, improved interference control via selective pre‑treatment, and harmonized reporting for regulatory and commercial use.
Related standards
- ISO 8157 - Fertilizers and soil conditioners - Vocabulary (normative reference in ISO 20702:2017).
Keywords: ISO 20702:2017, ion chromatography, fertilizers, soil conditioners, inorganic anions, fluoride, chloride, nitrite, thiocyanate, analytical method, fertilizer QA/QC.