ISO 18643:2016

Overview

ISO 18643:2016 specifies a standardized HPLC method for the determination of biuret content in liquid and solid urea-based fertilizers. The method defines sample preparation, reagents, HPLC operating conditions and calculation/reporting rules for quantitative measurement of biuret, a urea-condensation by‑product known to cause plant damage at elevated levels. The standard favors an acetonitrile–water mobile phase for extraction and reversed-phase separation on an amino/aminopropyl column, with UV detection.

Key topics and requirements

• Scope: Applicable to urea-based fertilizers (liquid and solid) using an HPLC procedure.
• Principle: Extract biuret with the acetonitrile/water mobile phase and separate by reversed‑phase HPLC; detect by UV.
• Reagents & safety: Uses HPLC‑grade acetonitrile (flammable, toxic) and water conforming to ISO 3696. Work in a fume hood and follow SDS guidance.
• Typical HPLC conditions: amino/aminopropyl column (4.6 × 250 mm, 5 µm), flow 1.0–1.3 ml/min, injection 10 µl, column temp 35 °C, detector wavelength 195 nm.
• Sample prep: Homogenize sample (sieving where required), dissolve 0.1–0.5 g test portion in mobile phase, ultrasonic extraction, filter prior to injection.
• Calibration & quantitation: Prepare biuret working standards from a stock solution, build a standard curve (duplicate injections), and calculate biuret mass fraction from peak areas.
• Precision: Ring test results and precision limits are provided; repeatability r = 0.022% (mass fraction) and reproducibility R = 0.102% (mass fraction).
• Alternatives & annexes: Annex B describes an acetonitrile‑free alternative with scope limitations; Annex A reports ring‑test data.
• Reporting: Test report must reference ISO 18643, include sample ID, results, sampling/analysis dates, and note if repeatability limits were met.

Applications

• Quality control and batch release testing for urea-based fertilizers.
• Regulatory compliance testing where limits on biuret are enforced.
• Supplier certification, specification verification, and incoming materials inspection.
• Research and development to monitor biuret formation in urea production or coating processes.
• Laboratory accreditation and inter‑laboratory comparisons (ring tests).

Who should use this standard

• Fertilizer manufacturers and production QC laboratories
• Commercial and government analytical laboratories
• Regulatory agencies and conformity assessment bodies
• Agronomists and product formulators concerned with plant safety

Related standards

• ISO 3696 - Water for analytical laboratory use (referenced for reagent water quality)
• ISO 5725‑2 - Used for statistical evaluation of precision in ring tests (precision assessment)

ISO 18643:2016 delivers a reproducible, HPLC-based protocol for accurate measurement of biuret, supporting product safety, regulatory compliance and consistent quality control in the fertilizer sector.