Overview
ISO/TS 20917:2023 specifies an ICP-OES (inductively coupled plasma–optical emission spectrometry) method for determining ammonium citrate, disodium‑EDTA soluble phosphorus and potassium in inorganic fertilizers. The Technical Specification covers the citrate‑EDTA extraction (0.11 M ammonium citrate / 0.033 M disodium‑EDTA, pH 7) and subsequent ICP‑OES analysis to quantify P and K in extract solutions. It is applicable to all inorganic fertilizer products (compound, complex, blends and straight concentrated fertilizers) and is intended primarily as an efficient screening method for high‑throughput laboratories.
Key topics and requirements
- Scope & applicability: Designed for inorganic fertilizers; not recommended for organic materials or phosphite‑containing liquids where phosphorus species differentiation is required.
- Extraction principle: Neutral ammonium citrate extracts soluble phosphate; EDTA chelates Ca/Mg/other cations to minimize interference and eliminate a water‑wash step.
- Extraction solution: Citrate‑EDTA solution prepared to pH 7.00 ± 0.02; shelf life limited (microbial degradation) - store in dark and use within ~3 weeks.
- ICP‑OES analysis: Nebulization of extract to plasma; element-specific emission wavelengths measured. Instrument conditions, calibration, wavelength selection and splitting are specified.
- Standards and reagents: Instructions for preparing calibration standards from reagent salts or commercial stocks and for internal standard/ionization buffer (e.g., Sc in CsCl + nitric acid; Be or Li alternatives noted).
- Quality control: Use of reference materials, duplicates, calibration checks, rinse solutions and internal standards. Sections on precision, repeatability and reproducibility are included.
- Sampling & sample prep: References ISO 14820‑1 and ISO 14820‑2 for sampling and preparation requirements.
Applications and who uses it
- Fertilizer testing laboratories seeking a rapid, multi‑element screening method for soluble P and K.
- Manufacturers and quality control teams for routine batch screening and production monitoring.
- Regulatory bodies and inspection labs using ICP‑OES for high sample throughput screening prior to confirmatory testing.
- Research groups evaluating soluble nutrient fractions in inorganic fertilizer formulations.
Benefits include automation, simultaneous multi‑element determination, reduced hazardous waste, and increased productivity compared with some traditional wet‑chemistry methods.
Related standards
- Sampling/sample preparation: ISO 14820‑1, ISO 14820‑2
- Vocabulary: ISO 8157
- Comparative methods and context: other fertilizer P/K test methods (e.g., EN 15959, EN 15477, ISO 22018) are referenced as having different precision characteristics - ISO/TS 20917:2023 is targeted for efficient screening rather than definitive compliance testing.
Keywords: ISO/TS 20917:2023, ICP‑OES method, ammonium citrate disodium‑EDTA, soluble phosphorus, soluble potassium, inorganic fertilizers, fertilizer testing, citrate‑EDTA extraction.