kSIST FprEN 17765:2026

• Abstract:

  This document specifies a method for the determination of the biuret content by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detector.; This document is applicable to organic and organo-mineral fertilizers containing urea.; This document is applicable to fertilizing products blends where a blend is a mix of at least two of the following products: fertilizers, liming materials, soil improvers, growing media, inhibitors, plant biostimulants and where organic matter is present in at least one of the products in the blend. In case a fertilizing product blend is composed only of inorganic products, the European Standard for inorganic fertilizers applies. Variations in analytical methods for fertilizing product blends can lead to differing results as some components or matrix interactions can affect the outcome. Validation procedures have shown that developed standard methods are robust and reliable across diverse product compositions, but possible interferences and unexpected results when analysing fertilizing product blends are possible.; NOTE 1 This method was tested only for one fertilizing product blend during the inter-laboratory study. The product tested was a liquid organo-mineral mixture of a liquid organic fertilizer, a growing medium and a non-microbial plant biostimulant.; NOTE 2 Nowadays, there is a method standardized as EN 15479 that allows the determination of biuret in urea by spectrophotometric detection. Organic and organo-mineral fertilizers contain organic matter and other compounds apart from urea that would interfere in a spectrophotometric method. HPLC allows an accurate determination of biuret by separating it from possible interfering compounds [2] [5].

• Status: Not Published
• Public Enquiry End Date: 01-Apr-2026
• ICS: 65.080 - Fertilizers
• Technical Committee: KAT - Soil quality
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 02-Nov-2026
• Due Date: 21-Dec-2026
• Directive: 2019/1009 - Regulation (EU) 2019/1009 of the European Parliament and of the Council of 5 June 2019 laying down rules on the making available on the market of EU fertilising products and amending Regulations (EC) No 1069/2009 and (EC) No 1107/2009 and repealing Regulation (EC) No 2003/2003 (Text with EEA relevance)
• Mandate: M/564 - Fertilising products in support of Regulation (EU) 2019/1009
• Mandate: M/564 AMD 1 - amending Implementing Decision C(2020) 612 as regards certain harmonised standards and standardisation deliverables, deadlines for their adoption and the duration of the validity of the standardisation request
• Mandate: M/564 AMD 2 - Commission Implementing decision amending Implementing Decision C(2020)612 as regards harmonised standards, the deadlines for the adoption of those standards and the duration of the validity of the standardisation request to the European Committee for Standardisation as regards the EU fertilising products in support of Regulation (EU) 2019/1009 of the European Parliament and of the Council
• Ref Project: FprEN 17765 - Organic and organo-mineral fertilizers - Determination of biuret content by high-performance liquid chromatography (HPLC)

• Revises: SIST-TS CEN/TS 17765:2023 - Organic and organo-mineral fertilizers - Determination of the biuret content by high-performance liquid chromatography (HPLC)
• Effective Date: 01-Mar-2026

kSIST FprEN 17765:2026 is the SIST publication identical to prEN 17765:2026, a draft European Standard from CEN. It specifies an HPLC method with UV detection for determining biuret in organic and organo-mineral fertilizers containing urea, and it also applies to fertilizing product blends with organic matter. It is aimed at laboratories and control teams that need a chromatographic method for matrices where spectrophotometric measurement can be affected by other compounds.

What does kSIST FprEN 17765:2026 specify?

kSIST FprEN 17765:2026 specifies the method, the reagents and apparatus, the sample preparation, the calculation of results, the precision statement, and the test report for biuret determination. The document is organized in clauses 1 to 10, with informative Annex A on interlaboratory precision and informative Annex ZA on the link to EU fertilising-product legislation.

Annex	What it covers
Annex A	Results of the interlaboratory study for precision
Annex ZA	Relationship with Regulation (EU) 2019/1009 and the corresponding essential requirements

The scope covers organic and organo-mineral fertilizers containing urea, plus fertilizing product blends where organic matter is present in at least one component. It also notes that blends made only of inorganic products fall under the European Standard for inorganic fertilizers. Sampling is handled outside the method itself, with references to other sampling standards.

What are the key requirements of kSIST FprEN 17765:2026?

kSIST FprEN 17765:2026 is built around extracting biuret, separating it chromatographically, and quantifying it against external standards. In practice, the user has to control the sample matrix, the calibration, and the chromatographic separation carefully because these factors drive the result.

• Clause 4, principle - The sample is extracted with an aqueous acetonitrile solution, separated by reversed-phase liquid chromatography, and detected with a UV detector. This matters because the chromatographic step isolates biuret from interfering compounds before measurement.
• Clauses 5 and 6, reagents and apparatus - The method uses analytical-grade reagents, HPLC-grade acetonitrile, water of specified conductivity, a biuret reference material, an HPLC system with UV detector, and an amino or amino-propyl column. This means the lab needs suitable solvent quality and a column that gives the required separation.
• Clauses 7.1 to 7.4, sampling and preparation - Sampling is outside the method, but the laboratory sample must be representative, prepared according to EN 1482-2, ground to pass a 0.50 mm sieve, extracted, diluted, and filtered; centrifugation is allowed if the filter loads too quickly. This is the stage where poor handling can distort the result.
• Clauses 7.2, 7.6 and 7.7, calibration and measurement - A six-level calibration set is prepared every day, each calibration solution is measured twice, and the test solution is analysed with the same procedure as the standards. This gives a daily external-standard calibration curve for converting peak area into biuret mass.
• Clause 7.5, HPLC conditions - The document gives recommended operating conditions, including column type, flow rate, injection volume, column temperature, detector wavelength, and run time, while allowing other conditions if they give the same separation effect. This flexibility is useful, but the separation must remain clean enough to avoid overestimation from overlapping compounds.
• Clause 8, calculations - Results are reported as g/kg of biuret, and a dry-matter expression is also provided using the dry matter content from prEN 17773. This lets users compare products on the same basis when moisture content differs.
• Clause 9 and Clause 10, precision and reporting - The method includes repeatability and reproducibility statements from an interlaboratory study, and the report must identify the sample, the method used, the result, sampling details if known, and any relevant deviations. This supports traceable quality control and defensible reporting.

What terms does kSIST FprEN 17765:2026 define?

• Biuret - Imidodicarbonic diamide, a condensed urea formed from two urea molecules.
• HPLC - High-performance liquid chromatography, the separation technique used here to isolate biuret before detection.
• UV detector - The detector used to measure the chromatographic peaks at the specified wavelength.
• Calibration curve - The relationship between known standard amounts and measured peak area, used to calculate biuret in the sample.
• Repeatability - The closeness of two results obtained under the same laboratory, operator, equipment, and short time interval.
• Reproducibility - The closeness of results obtained in different laboratories with different operators and equipment.
• Dry matter content - The sample dry matter used to convert results to a dry-matter basis.

Who uses kSIST FprEN 17765:2026?

kSIST FprEN 17765:2026 is used by fertilizer laboratories, quality-control teams, and manufacturers of organic and organo-mineral fertilizers. It is also relevant to conformity assessment bodies and regulators working on EU fertilising products. The method is especially useful for products containing urea, where biuret has to be measured in complex organic matrices and in product blends.

What changed in kSIST FprEN 17765:2026 from the previous edition?

kSIST FprEN 17765:2026 supersedes CEN/TS 17765:2022. The European foreword states three significant technical changes: the technical specification has been adopted as a European Standard with the addition of Annex ZA, the scope has been updated with clarification on fertilizing product blends, and Clause 9 on precision together with Annex A on interlaboratory results has been added.

Which standards are used with kSIST FprEN 17765:2026?

Standard	Contribution
EN 12944-1:1999	General fertilizer and liming-material vocabulary
EN 12944-2:1999	Fertilizer-specific vocabulary
EN 1482-2:2024	General sample preparation provisions
prEN 17773:2026	Dry matter content used for dry-matter-based results
EN 1482-1:2024	Recommended general sampling provisions
EN 1482-3:2024	Recommended sampling of static heaps
EN 15479	Spectrophotometric biuret method for urea, noted as less suitable for organic matrices
ISO 5725-1	General principles for precision statistics
ISO 5725-2	Repeatability and reproducibility calculation method

What does the kSIST FprEN 17765:2026 document contain?

kSIST FprEN 17765:2026 contains a full laboratory method rather than only a definition of the analyte. Clause 7 gives the working procedure for calibration, sample extraction, HPLC analysis, and system washing after the run. Clause 8 gives the formulas for reporting biuret as received and on a dry-matter basis. Clause 9 summarizes precision from an interlaboratory study, while Annex A gives the study design, sample set, and statistical results. Annex ZA maps the method to the essential requirements of Regulation (EU) 2019/1009 for EU fertilising products.

SLOVENSKI STANDARD
oSIST prEN 17765:2026
01-marec-2026
Organska in organsko-mineralna gnojila - Določanje biureta s tekočinsko
kromatografijo visoke ločljivosti (HPLC)
Organic and organo-mineral fertilizers - Determination of biuret content by high-
performance liquid chromatography (HPLC)
Organische und organisch-mineralische Düngemittel - Bestimmung des Biuretgehalts
mittels Hochleistungs-Flüssigkeitschromatographie (HPLC)
Engrais organiques et organo-minéraux - Détermination de la teneur en biuret par
chromatographie liquide à haute performance (HPLC)
Ta slovenski standard je istoveten z: prEN 17765
ICS:
65.080 Gnojila Fertilizers
oSIST prEN 17765:2026 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 17765:2026
oSIST prEN 17765:2026
DRAFT
EUROPEAN STANDARD
prEN 17765
NORME EUROPÉENNE
EUROPÄISCHE NORM
January 2026
ICS 65.080 Will supersede CEN/TS 17765:2022
English Version
Organic and organo-mineral fertilizers - Determination of
biuret content by high-performance liquid
chromatography (HPLC)
Engrais organiques et organo-minéraux - Organische und organisch-mineralische Düngemittel -
Détermination de la teneur en biuret par Bestimmung des Biuretgehalts mittels Hochleistungs-
chromatographie liquide à haute performance (HPLC) Flüssigkeitschromatographie (HPLC)
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 260.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17765:2026 E
worldwide for CEN national Members.

oSIST prEN 17765:2026
prEN 17765:2026 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 6
5 Reagents . 6
6 Apparatus . 6
7 Procedure . 7
7.1 Sampling . 7
7.2 Calibration solutions . 7
7.3 Preparation of the sample . 8
7.4 Extraction of the sample and preparation of the test solution. 8
7.5 HPLC conditions . 8
7.6 Preparation of the standard curve . 9
7.7 Determination of biuret in the test solutions . 9
8 Calculations . 9
9 Precision . 10
9.1 Inter-laboratory study . 10
9.2 Repeatability . 10
9.3 Reproducibility . 10
10 Test report . 11
Annex A (informative) Results of the interlaboratory study . 12
A.1 Interlaboratory tests . 12
A.2 Statistical results for the determination of biuret . 13
Annex ZA (informative) Relationship between this European Standard and the essential
requirements of Regulation (EU) 2019/1009 making available on the market of EU
fertilising products aimed to be covered . 14
Bibliography . 15

oSIST prEN 17765:2026
prEN 17765:2026 (E)
European foreword
This document (prEN 17765:2026) has been prepared by Technical Committee CEN/TC 260 “Fertilizers
and liming materials”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede CEN/TS 17765:2022.
Compared to the previous edition, prEN 17765:2026 includes the following significant technical changes:
— the CEN Technical Specification has been adopted as a European Standard including the addition of
Annex ZA;
— the Scope (Clause 1) has been updated including a clarification on fertilizing product blends;
— Clause 9 (Precision) and Annex A (Results of the interlaboratory study) have been added.
This document has been prepared under a Standardization Request addressed to CEN by the European
Commission. The Standing Committee of the EFTA States subsequently approves these requests for its
Member States.
For the relationship with EU Legislation, see informative Annex ZA, which is an integral part of this
document.
oSIST prEN 17765:2026
prEN 17765:2026 (E)
Introduction
This document defines a test method for the determination of the biuret content to be used for organic
and organo-mineral fertilizers.
When heating urea near or above its melting point (132 °C) during the manufacturing of urea, ammonia
slowly evolves and several different substances, including biuret, are formed. Excessively high
concentrations of biuret can have detrimental effects on plants growth.

oSIST prEN 17765:2026
prEN 17765:2026 (E)
1 Scope
This document specifies a method for the determination of the biuret content by high-performance liquid
chromatography (HPLC) with ultraviolet (UV) detector.
This document is applicable to organic and organo-mineral fertilizers containing urea.
This document is applicable to fertilizing products blends where a blend is a mix of at least two of the
following products: fertilizers, liming materials, soil improvers, growing media, inhibitors, plant
biostimulants and where organic matter is present in at least one of the products in the blend. In case a
fertilizing product blend is composed only of inorganic products, the European Standard for inorganic
fertilizers applies. Variations in analytical methods for fertilizing product blends can lead to differing
results as some components or matrix interactions can affect the outcome. Validation procedures have
shown that developed standard methods are robust and reliable across diverse product compositions,
but possible interferences and unexpected results when analysing fertilizing product blends are possible.
NOTE 1 This method was tested only for one fertilizing product blend during the inter-laboratory study. The
product tested was a liquid organo-mineral mixture of a liquid organic fertilizer, a growing medium and a non-
microbial plant biostimulant.
NOTE 2 Nowadays, there is a method standardized as EN 15479 that allows the determination of biuret in urea
by spectrophotometric detection. Organic and organo-mineral fertilizers contain organic matter and other
compounds apart from urea that would interfere in a spectrophotometric method. HPLC allows an accurate
determination of biuret by separating it from possible interfering compounds [2] [5].
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 12944-1:1999, Fertilizers and liming materials — Vocabulary — Part 1: General terms
EN 12944-2:1999, Fertilizers and liming materials — Vocabulary — Part 2: Terms relating to fertilizers
EN 1482-2:2024, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part
2: General sample preparation provisions
prEN 17773:2026, Organic and organo-mineral fertilizers — Determination of the dry matter content
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12944-1:1999 and
EN 12944-2:1999 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp/
— IEC Electropedia: available at https://www.electropedia.org/

As impacted by EN 12944-1:1999/AC:2000.
As impacted by EN 12944-2:1999/AC:2000.
Under preparation.
oSIST prEN 17765:2026
prEN 17765:2026 (E)
3.1
biuret
imidodicarbonic diamide
member of the class of condensed ureas, formed by the condensation of two molecules of urea
Note 1 to entry: Condensed ureas are the compounds formed by the condensation of two or more molecules of
urea.
4 Principle
The biuret content of the fertilizer sample is extracted with an aqueous acetonitrile solution and
separated by reversed-phase liquid chromatography. Detection of peaks is performed using an UV
detector. Quantification is performed with calibration curve using external standards.
5 Reagents
All reagents shall be of recognized analytical grade.
5.1 Water.
All water shall have a specific conductivity of not more than 0,2 ms/m at 25 °C and shall be free of the
compounds to be detected.
5.2 Acetonitrile, HPLC grade, ≥ 99,9 %.
5.3 Biuret.
The purity of these reagents shall be ≥ 97 %, and the calculation of biuret content within fertilizer should
be based on the purity claimed on the label.
5.4 Eluent, used for HPLC (mobile phase), acetonitrile: water 85 : 15 (volume fraction).
For the preparation of the eluent, the following tasks shall be performed:
a) mix 150 ml water (5.1) with 850 ml acetonitrile (5.2);
b) filter the solution by 0,22 µm membrane filter (6.5) as pretreatment;
c) ultrasonic degas (6.4) for 10 min before used, alternatively an in-line degasser can be used.
5.5 Biuret standard solution (0,5 mg/ml).
For the preparation of the biuret standard solution (0,5 mg/ml), the following tasks shall be performed:
a) weigh approximately 0,50 g to the nearest 0,1 mg of biuret (5.3) and dissolve it by mobile phase (5.4);
b) transfer it into a 1 l volumetric flask;
c) bring to volume with mobile phase (5.4) and mix it thoroughly.
6 Apparatus
6.1 High performance liquid chromatograph, with UV detector.
6.2 Chromatographic column, amino column or amino-propyl column.
6.3 Injection loop.
oSIST prEN 17765:2026
prEN 17765:2026 (E)
6.4 Ultrasonic bath.
6.5 Membrane filter, for organic solvents, pore size of 0,22 µm.
6.6 Micro-syringe, with a volume between 5 µl and 50 µl.
The micro-syringe is only necessary in case of using manual injection.
6.7 Syringe-driven filter, syringe with membrane filter for organic solvents (for example
Polytetrafluoroethylene, PTFE), pore size of 0,22 µm.
6.8 Centrifuge.
6.9 Sieve, aperture size of
...