ISO 25705:2016

Overview

ISO 25705:2016 specifies validated analytical methods for the determination of urea condensates in fertilizers by high-performance liquid chromatography (HPLC). It covers two methods:

• Method A - quantification of isobutylidene diurea (IBDU) and crotonylidene diurea (CDU);
• Method B - determination of methylene‑urea (MU) oligomers (soluble oligomers such as MDU, DMTU, TMTU and urea).

The standard applies to fertilizers that do not contain interfering organic compounds and supports regulatory declaration of these substances and their contribution to nitrogen content.

Key topics and technical requirements

• Sample preparation: Follow ISO 14820-2 guidance; for Method A a representative ground sample (<0.2 mm) is typically extracted (example: 1 g → 1 000 ml water), treated in an ultrasonic bath and stirred prior to dilution and filtration.
• HPLC conditions (Method A example):
  • Column: C18 reversed-phase (silica-based)
  • Detector: UV, 200 nm
  • Mobile phase: acetonitrile/water 10/90 (v/v)
  • Flow: 1.0 ml/min, injection 20 µl, ambient temperature
• Calibration and quantification: Use stock solutions of pure IBDU/CDU and prepare calibration standards (e.g., 10, 25, 50 mg/l). Calculations can be manual or PC‑aided; conversion factors to nitrogen content are provided (IBDU: 0.322; CDU: 0.326).
• Method B specifics: MU oligomers are extracted with boiling water and separated by HPLC; characteristic peaks include urea, methylene‑diurea, dimethylene‑triurea and trimethylene‑tetraurea.
• Quality & performance: The standard contains inter‑laboratory precision data, repeatability and reproducibility information, and detailed instructions for calibration, measurement and reporting.
• Limitations: Not intended for fertilizers containing interfering organic compounds that co-elute or affect detection.

Applications and users

ISO 25705 is used by:

• Analytical laboratories performing fertilizer composition testing
• Fertilizer manufacturers for quality control and product specification
• Regulatory bodies and conformity assessors verifying compliance with nutrient labeling and fertilizer regulations (e.g., Regulation (EC) 2003/2003)
• R&D teams developing controlled‑release or urea‑based fertilizer formulations

Benefits include reliable quantification of urea condensates, traceable HPLC procedures, and standardised reporting for market and regulatory acceptance.

Related standards

• ISO 3696 - Water for analytical laboratory use
• ISO 14820-2 - Sampling and sample preparation for fertilizers
• EN 12944‑1 / EN 12944‑2 - Vocabulary related to fertilizers and liming materials

Keywords: ISO 25705, fertilizers, urea condensates, HPLC, IBDU, CDU, methylene‑urea, MU oligomers, fertilizer testing, nutrient analysis.