Overview
ISO 6650:2023 specifies a validated analytical method for the simultaneous determination of N-(n‑butyl) thiophosphoric triamide (NBPT) and dicyandiamide (DCD) in fertilizers using high‑performance liquid chromatography (HPLC). The standard targets fertilizers, soil conditioners and beneficial substances and is intended for routine laboratory analysis to support quality control, regulatory compliance and research into nitrogen stabilizers (urease and nitrification inhibitors).
Key Topics and Technical Requirements
- Scope and principle
- Simultaneous HPLC determination of NBPT (urease inhibitor) and DCD (nitrification inhibitor) using UV/PDA detection.
- Reagents and standards
- Use HPLC‑grade acetonitrile and water meeting ISO 3696; certified NBPT and DCD reference materials; stock solutions (1 000 mg/L).
- Sample preparation
- Solid fertilizers: reduce to 100 g, grind to pass 0.5 mm (ISO 8358).
- Test solution: 0.1–3 g sample in 100 mL ultrapure water, ultrasonic extraction 20 min, filter 0.45 µm.
- HPLC conditions (recommended)
- Column: 250 × 4.6 mm C18 reversed phase.
- Injection: 10 µL; flow rate: 1.0 mL/min.
- Detector: PDA (recommended) or UV - 214 nm for DCD, 205 nm for NBPT (single‑wavelength labs may use 214 nm for both).
- Eluent: acetonitrile/water gradient (starts 5% ACN → 25% ACN at 10 min → return to 5% by 17 min; total run ~31 min).
- Quantification and calculation
- Standard curves from prepared working standards (5–100 mg/L NBPT; 1–100 mg/L DCD).
- Result calculated as mass fraction (%) using measured concentration, sample mass and dilution factor; average of two replicates rounded to three significant figures.
- Precision and validation
- Repeatability (r) and reproducibility (R) expressed as functions of mass fraction w:
- DCD repeatability: r = 0.067w − 0.014
- NBPT repeatability: r = 0.074w − 0.011
- DCD reproducibility: R = 0.160w − 0.021
- NBPT reproducibility: R = 0.137w + 0.034
- Interlaboratory ring test data and typical chromatograms are provided in annexes.
Applications and Users
- Who uses ISO 6650:2023
- Fertilizer manufacturers performing product QC and formulation verification.
- Independent testing laboratories and national regulatory bodies enforcing label claims and safe use.
- Agricultural researchers studying nitrogen stabilizers (NBPT, DCD) and environmental impacts.
- Practical value
- Enables simultaneous, time‑saving analysis of NBPT and DCD, reducing solvent and waste.
- Supports product labeling accuracy, regulatory compliance, and environmental monitoring for nitrification/urease inhibitors.
Related Standards
- ISO 3696 - Water for analytical laboratory use
- ISO 8157 - Fertilizers, soil conditioners and beneficial substances - Vocabulary
- ISO 8358 - Solid fertilizers - Preparation of samples for chemical and physical analysis
Keywords: ISO 6650:2023, NBPT, DCD, HPLC method, fertilizers, soil conditioners, simultaneous determination, urease inhibitor, nitrification inhibitor, analytical standard, laboratory quality control.
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