CEN/TC 260
Date: 2025-10
prEN 17403:2026
Secretariat: DIN
Inorganic fertilizers — Determination of cold water insoluble nitrogen and hot water insoluble nitrogen in solid urea formaldehyde and methylene urea slow-release fertilizers and determination of the solubility of nutrient polymers in phosphate buffer solution with a pH of 7,5 at 100 °C
Einführendes Element — Haupt-Element — Ergänzendes Element
Élément introductif — Élément central — Élément complémentaire
CCMC will prepare and attach the official title page.
Contents Page
4 Sampling and sample preparation 7
5 Determination of the mass fraction of CWIN in solid UF/MU 7
5.5 Calculation and expression of results 8
6 Determination of the mass fraction of HWIN in solid UF/MU 8
6.5 Calculation and expression of results 9
Annex A (informative) Results of the inter-laboratory study 12
This document (prEN 17403:2026) has been prepared by Technical Committee CEN/TC 260 “Fertilizers and liming materials”, the secretariat of which is held by DIN.
This is currently submitted to CEN Enquiry.
This document will supersede CEN/TS 17403:2021.
prEN 17403:2026 includes the following significant technical changes with respect to CEN/TS 17403:2021:
a) The CEN Technical Specification has been adopted as a European Standard.
b) Normative references (Clause 2) and Terms and definitions (Clause 3) have been updated.
c) The type of quantitative filter paper has been better specified.
d) The use of the combustion method to determine the residue on the filter has been contemplated.
e) The method for determining total nitrogen has been specified.
f) Clause 8 on precision has been added.
g) Annex A with the results of the inter-laboratory study has been added.
h) The Bibliography has been updated.
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.
Solid urea formaldehyde and methylene urea slow-release fertilizers are non-coated and chemically synthesized nitrogen fertilizers with slow-release effect. In 1924, the first slow-release fertilizer patent in the world was issued to urea formaldehyde (UF) and in 1955, UF was put into commercial production as the oldest slow-release fertilizer.
WARNING — Users of this document should be familiar with normal laboratory practice. This document does not purport to address all of the safety issues, if any, associated with its use. It is the responsibility of the user to establish appropriate health and safety practices and to ensure compliance with any national regulatory conditions.
IMPORTANT — It is absolutely essential that tests conducted according to this document are carried out by suitably trained staff.
1.0 Scope
This document specifies a method for the determination of the cold and hot water insoluble nitrogen content in solid urea formaldehyde and methylene urea slow-release fertilizers and for the determination of the solubility of nutrient polymers in a phosphate buffer solution with a pH of 7,5 at 100 °C, in their pure form in inorganic fertilizers.
This document is not applicable to the following nutrient polymers: liquid methylene urea.
2.0 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 1482-2, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part 2: General sample preparation provisions
EN 12944-1,[1] Fertilizers, liming materials and inhibitors — Vocabulary — Part 1: General terms
EN 12944-2,[2] Fertilizers, liming materials and inhibitors — Vocabulary — Part 2: Terms relating to fertilizers
EN 15478, Inorganic fertilizers — Determination of total nitrogen in urea, methylene-urea and urea formaldehyde
ISO 5315, Fertilizers — Determination of total nitrogen content — Titrimetric method after distillation
3.0 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 12944-1 and EN 12944-2 and the following apply.
ISO and IEC maintain terminology 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/
3.1
urea formaldehyde
UF
slow-release nitrogenous fertilizer obtained by the reaction between urea and formaldehyde to produce molecular chains of general formula NH2-CO-NH(CH2NHCONH)nH
3.2
methylene urea
MU
slow-release nitrogenous fertilizer obtained by the reaction between urea and formaldehyde to produce oligomers such as MDU (methylendiurea), DMTU (dimethylentriurea), TMTU (trimethylentetraurea), TMPU (tetramethylenpentaurea) and higher counterparts
3.3
nutrient polymers
component material of fertilizing products consisting of polymers exclusively made up of virgin material substances and mixtures, where the purpose of the polymerisation is to control the release of nutrients from one or more of the monomer substances
3.4
virgin material substances and mixtures
component material of fertilizing products consisting of virgin material substances and mixtures
Note 1 to entry: Excluded are the following products: waste and by-products according to [4], materials formerly having constituted in waste or by-products, animal by-products or derived products and polymers.
3.5
cold water insoluble nitrogen
CWIN
insoluble nitrogen fractions in urea formaldehyde or methylene urea products that are insoluble in phosphate buffer solution (pH 7,5) or distilled water at 25 °C during a 15 min period
[SOURCE: ISO 19670:2017, 3.2]
3.6
cold water soluble nitrogen
CWSN
soluble nitrogen fractions in urea formaldehyde or methylene urea products that are soluble in phosphate buffer solution (pH 7,5) or distilled water at 25 °C during a 15 min period
Note 1 to entry: CWSN = Total nitrogen − CWIN.
[SOURCE: ISO 19670:2017, 3.3]
3.7
hot water insoluble nitrogen
HWIN
insoluble nitrogen fractions in urea formaldehyde or methylene urea products that are insoluble in phosphate buffer solution (pH 7,5) at 100 °C during a 30 min period
[SOURCE: ISO 19670:2017, 3.4]
3.8
hot water soluble nitrogen
HWSN
soluble nitrogen fractions in urea formaldehyde or methylene urea products and in nutrient polymers that are soluble in phosphate buffer solution (pH 7,5) at 100 °C during a 30 min period
Note 1 to entry: HWSN = Total nitrogen − HWIN.
[SOURCE: ISO 19670:2017, 3.5, modified – “and in nutrient polymers” has been added to the definition.]
3.9
hot water soluble nitrogen only
HWSN only
soluble nitrogen fractions in urea formaldehyde or methylene urea products that are soluble in phosphate buffer solution (pH 7,5) at 100 °C during a 30 min period and insoluble in phosphate buffer solution (pH 7,5) or distilled water at 25 °C during a 15 min period
Note 1 to entry: HWSN only = HWSN − CWSN = CWIN − HWIN.
[SOURCE: ISO 19670:2017, 3.6]
4.0 Sampling and sample preparation
4.1 Sampling
Sampling is not part of the method specified in this document. A recommended sampling method is given in EN 1482-1 [1].
It is important that the laboratory receives a sample that is representative of both the product under consideration and the given analysis. The sample should not have been damaged or changed during transport or storage.
4.1.1 Sample preparation
Sample preparation shall be carried out in accordance with EN 1482-2.
For the size reduction of samples to be used for the determinations according to Clause 5 and Clause 6 the laboratory sample shall be reduced to 100 g. Grind this test sample in the grinder. Avoid any warming of the sample on grinding. Take the portion of the grinded sample that passed at 0,500 mm sieve and pass it through a 0,212 mm sieve; use only the portion of the grinded sample that does not pass the 0,212 mm sieve. Put the prepared samples into clean and dry bottles to be used for further analysis.
5.0 Determination of the mass fraction of CWIN in solid UF/MU
5.1 Principle
Extraction of the test portion in phosphate buffer solution (pH 7,5) or distilled water at 25 °C. Filtration of the insoluble residue, washing and determination of the nitrogen content in the insoluble residue.
5.1.1 Reagents
5.2.1 Distilled water.
5.2.2 Phosphate buffer solution, pH 7,5.
Dissolve 14,3 g KH2PO4 and 91,0 g K2HPO4 in water and dilute to 1 l. Dilute 100 ml of this solution to 1 l.
5.2.3 Anhydrous ethanol.
5.2.4 Reagents listed in ISO 5315 for the determination of the nitrogen content.
5.1.2 Apparatus
5.3.1 Usual laboratory apparatus.
5.3.2 Water bath, capable of being maintained at (25 ± 2) °C.
5.3.3 Quantitative filter paper (intermediate speed), nitrogen free [3]
5.3.4 Apparatus listed in ISO 5315 for the determination of the nitrogen content.
5.1.3 Procedure
5.4.1 Two analyses shall be performed simultaneously for the determination.
5.4.2 Place 1 g to 1,4 g test portion (accurate to 0,000 1 g) in a 50 ml beaker and wet the test portion with ethanol (5.2.3). Add 20 ml phosphate buffer solution (5.2.2) or distilled water (5.2.1) and let stand for 15 min in the water bath maintained at (25 ± 2) °C (5.3.2) and stir at 5 min intervals during standing. Transfer the supernatant to a piece of filter paper (5.3.3) in long-stem funnel and wash the residue four or five times by decanting with water (5.2.1) at (25 ± 2) °C. Finally, transfer all the residue to the filter paper and complete washing with water (5.2.1) at (25 ± 2) °C until the filtrate measures 250 ml. Determine the nitrogen content in the filter paper and the residue in accordance with ISO 5315.
Alternatively, a combustion method can be used.
5.4.3 Carry out a blank test at the same time as the determination, using the same procedure, using the same reagents, but omitting the test portion.
5.1.4 Calculation and expression of results
The CWIN content, w1, expressed as a mass fraction in percent, is given by Formula (1):
(1)
where
V1 is the volume, in ml, of sodium hydroxide standard solution used for the blank test;
V2 is the volume, in ml, of sodium hydroxide standard solution used for the determination;
c1 is the concentration, in mol/l, of sodium hydroxide standard solution used;
m1 is the mass, in g, of the test portion.
The calculation results are accurate to two digits after the decimal point. The determination result is the arithmetic average of the duplicate determination results.
6.0 Determination of the mass fraction of HWIN in solid UF/MU
6.1 Principle
Extraction of the test portion in phosphate buffer solution (pH 7,5) (5.2.2) at 100 °C. Filtration of the insoluble residue, washing and determination of the nitrogen content in the insoluble residue.
6.1.1 Reagents
6.2.1 Reagents listed in 5.2.
6.2.2 Celite.
6.1.2 Apparatus
6.3.1 Usual laboratory apparatus.
6.3.2 Water bath, capable of being maintained at (100 ± 2) °C.
6.3.3 Apparatus listed in 5.3.3 and 5.3.4.
6.1.3 Procedure
6.4.1 Two analyses shall be performed simultaneously for the determination.
6.4.2 Place 0,5 g of the test portion (accurate to 0,000 1 g) in a 250 ml tall-form beaker. Add 100 ml of the phosphate buffer solution (5.2.2) at 100 °C using a graduated cylinder to the test portion, stir, cover with a watch glass and immerse promptly in a boiling water bath (6.3.2) so that the liquid in the beaker is below the water level in the water bath. Maintain the water bath at 100 °C, check with a thermometer and stir at 10 min intervals. After exactly 30 min, remove the beaker from the water bath and filter promptly through a piece of filter paper (5.3.3). If filtration takes more than 4 min, discard determination: in this case repeat the determination adding 1 g celite (6.2.2) as filter-aid just before removing the beaker from the water bath, stir and filter.
6.4.3 Wash the insoluble residue completely onto the filter paper with boiling water (5.2.1) and continue washing with water (5.2.1) at (100 ± 2) °C until the total volume used is 100 ml. Complete washing before the filtrate becomes cloudy or its temperature drops to below 60 °C. Determine total nitrogen in the filter paper and residue in accordance with ISO 5315.
Alternatively, a combustion method can be used.
6.4.4 Carry out a blank test at the same time as the determination, using the same procedure and reagents, but omitting the test portion.
6.1.4 Calculation and expression of results
The HWIN content, w2, expressed as a mass fraction in percent, is given by Formula (2):
(2)
where
V3 is the volume, in ml, of sodium hydroxide standard solution used for the blank test;
V4 is the volume, in ml, of sodium hydroxide standard solution used for the determination;
c2 is the concentration, in mol/l, of sodium hydroxide standard solution used;
m2 is the mass, in g, of the test portion.
The calculation results are accurate to two digits after the decimal point. The determination result is the arithmetic average of the duplicate determination results.
7.0 Determination of the solubility of nutrient polymers in phosphate buffer solution with a pH of 7,5 at 100 °C
The HWSN content, w3, expressed as a mass fraction in percent, shall be calculated in accordance with Formula (3):
(3)
where
w2 is the HWIN content, expressed as a mass fraction, in %;
w4 is the total nitrogen content, expressed as a mass fraction, in %, determined in accordance with EN 15478.
8.0 Precision
8.1 Inter-laboratory study
Details of inter-laboratory studies on the precision of the method are summarized in Annex A. Repeatability and reproducibility were calculated according to ISO 5725-2 and ISO 5725-3.
It is possible that the values derived from this study are not applicable to concentration ranges and matrices other than those given.
8.1.1 Repeatability
The absolute difference between two independent single test results, obtained using the same method on identical test material in the same laboratory by the same operator using the same equipment within a short interval of time, will in no more than 5 % of the cases be greater than the repeatability limit r given in Table 1.
8.1.2 Reproducibility
The absolute difference between two independent single test results, obtained using the same method on identical test material in different laboratories with different operators using different equipment, will in no more than 5 % of the cases be greater than the reproducibility limit R given in Table 1.
Table 1 — Mean values, repeatability and reproducibility limits
Sample |
| r | R |
% | % | % | |
Solid methylene urea, cold water insoluble nitrogen | 20,9 | 0,9 | 2,7 |
Solid methylene urea, hot water insoluble nitrogen | 9,1 | 0,6 | 2,7 |
Solid urea formaldehyde, cold water insoluble nitrogen | 30,0 | 0,3 | 1,0 |
Solid urea formaldehyde, hot water insoluble nitrogen | 20,0 | 1,4 | 1,6 |
9.0 Test report
The test report shall contain at least the following information:
a) all information necessary for the complete identification of the sample;
b) the test method used with reference to this document, including its year of publication;
c) the test results obtained;
d) date of sampling and sampling procedure (if known);
e) date when the analysis was finished;
f) whether the requirement of the repeatability limit has been fulfilled;
g) all operating details not specified in this document, or regarded as optional, together with details of any incidents occurred when performing the method, which might have influenced the test result(s).
The precision of the method has been determined in the year 2025 in an inter-laboratory study with 5 laboratories participating and carried out on 2 samples of inorganic fertilizers. The statistical results are given in Table A.1 and Table A.2.
Table A.1 — Statistical results for determination of cold-water insoluble nitrogen in inorganic fertilizers
Sample | Solid methylene urea | Solid urea formaldehyde |
L | 5 | 5 |
LA | 5 | 5 |
N | 20 | 20 |
NA | 20 | 20 |
O | 0 | 0 |
x̿ | 20,9 | 30,0 |
sR | 1,0 | 0,4 |
sr | 0,3 | 0,1 |
sI | 0,3 | 0,2 |
RSDR | 4,6 | 1,2 |
RSDr | 1,4 | 0,3 |
R | 2,7 | 1,0 |
r | 0,9 | 0,3 |
HorRat | 1,8 | 0,5 |
Key |
| |
L | number of participating laboratories; | |
LA | number of laboratories after elimination of outliers; | |
N | number of all analytical values; | |
NA | number of analytical values after rejection of outliers; | |
O | percentage of outliers, in %; | |
x̿ | total mean of results (without outliers), in %; | |
sR | reproducibility standard deviation in %; | |
sr | repeatability standard deviation in %; | |
sI | intermediate standard deviation in %; | |
RSDR | relative reproducibility standard deviation, in %; | |
RSDr | relative repeatability standard deviation, in %; | |
R | reproducibility limit (2,77 sR), in %; | |
r | repeatability limit (2,77 sr), in %; | |
HorRat | HorRat index. | |
Table A.2 — Statistical results for determination of hot water insoluble nitrogen in inorganic fertilizers
Sample | Solid methylene urea | Solid urea formaldehyde |
L | 5 | 5 |
LA | 5 | 5 |
N | 20 | 20 |
NA | 20 | 20 |
O | 0 | 0 |
x̿ | 9,1 | 20,0 |
sR | 0,9 | 0,6 |
sr | 0,2 | 0,5 |
sI | 0,3 | 0,5 |
RSDR | 10,4 | 2,9 |
RSDr | 2,5 | 2,5 |
R | 2,7 | 1,6 |
r | 0,6 | 1,4 |
HorRat | 3,6 | 1,1 |
Key |
| |
L | number of participating laboratories; | |
LA | number of laboratories after elimination of outliers; | |
N | number of all analytical values; | |
NA | number of analytical values after rejection of outliers; | |
O | percentage of outliers, in %; | |
x̿ | total mean of results (without outliers), in %; | |
sR | reproducibility standard deviation in %; | |
sr | repeatability standard deviation in %; | |
sI | intermediate standard deviation in %; | |
RSDR | relative reproducibility standard deviation, in %; | |
RSDr | relative repeatability standard deviation, in %; | |
R | reproducibility limit (2,77 sR), in %; | |
r | repeatability limit (2,77 sr), in %; | |
HorRat | HorRat index. | |
[1] EN 1482-1, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part 1: General sampling provisions
[2] ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method
[3] ISO 5725-3, Accuracy (trueness and precision) of measurement methods and results — Part 3: Intermediate precision and alternative designs for collaborative studies
[4] 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
[5] Directive 2008/98/EC of the European Parliament and of the Council of 19 November 2008 on waste and repealing certain Directives
[6] ISO 19670:2017, Fertilizers and soil conditioners — Solid urea aldehyde slow release fertilizer — General requirements
[7] Method BNL-N-12, Determination of the activity index and of nitrogen insoluble in cold water
[8] ISO 20620, Fertilizers and soil conditioners — Determination of total nitrogen by combustion
A revision is under preparation. Stage at the time of preparation: prEN 12944-1:2026 ↑
A revision is under preparation. Stage at the time of preparation: prEN 12944-2:2026 ↑
Whatman Grade 2 and Sartorius Grade 391 are examples of suitable products available commercially. This information is given for the convenience of users of this European Standard and does not constitute an endorsement by CEN of these products. ↑
