CEN/TC 260

Date: 2025-10

prEN 15478:2026

Secretariat: DIN

Inorganic fertilizers — Determination of total nitrogen in urea, methylene-urea and urea formaldehyde

Einführendes Element — Haupt-Element — Ergänzendes Element

Élément introductif — Élément central — Élément complémentaire

CCMC will prepare and attach the official title page.

Contents Page

European foreword 3

1 Scope 4

2 Normative references 4

3 Terms and definitions 4

4 Principle 4

5 Reagents 4

6 Apparatus 5

7 Sampling and sample preparation 10

8 Procedure 10

8.1 Procedure for the determination of total nitrogen in urea 10

8.1.1 Preparation of the solution 10

8.1.2 Analysis of the solution 10

8.1.3 Blank 10

8.1.4 Control test 11

8.2 Procedure for the determination of total nitrogen in methylene-urea and urea formaldehyde 11

8.2.1 Preparation of the solution 11

8.2.2 Analysis of the solution 11

8.2.3 Blank 11

8.2.4 Control test 11

9 Calculation and expression of the result 12

9.1 Calculation and expression of the result of total nitrogen in urea 12

9.2 Calculation and expression of the result of total nitrogen in methylene-urea and urea formaldehyde 12

10 Precision 13

10.1 Precision of the method aiming to determine total nitrogen in urea 13

10.1.1 Inter-laboratory study 13

10.1.2 Repeatability 13

10.1.3 Reproducibility 13

10.2 Precision of the method aiming to determine total nitrogen in methylene-urea and urea formaldehyde 13

10.2.1 Inter-laboratory study 13

10.2.2 Repeatability 13

10.2.3 Reproducibility 13

11 Test report 14

Annex A (informative) Results of the inter-laboratory tests 15

Annex B (informative) Results of the inter-laboratory study 16

Bibliography 18

European foreword

This document (prEN 15478:2026) 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 EN 15478:2009.

prEN 15478:2026 includes the following significant technical changes with respect to EN 15478:2009:

— The scope has been broadened by adding the determination of the content of total nitrogen in methylene-urea and urea formaldehyde and the title has been adjusted accordingly;

— The method has been technically revised according to the broader scope;

— The statistical results relating to the inter-laboratory study of the determination of total nitrogen in methylene urea and urea formaldehyde have been added (10.2 and Annex B).

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.

This document specifies a method for the determination of the content of total nitrogen in urea, methylene-urea and urea formaldehyde in their pure form in inorganic fertilizers.

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

For the purposes of this document, the terms and definitions given in EN 12944‑1 and EN 12944‑2 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/

The nitrogen is transformed quantitatively into ammoniacal salt by boiling in the presence of sulfuric acid. The ammoniacal solution thus obtained is distilled through an alkaline medium, the distillate being collected in an excess of standard sulfuric acid. The excess acid is titrated by means of a standard alkaline solution.

Use only reagents of recognized analytical grade and distilled or demineralized water, free from carbon dioxide and all nitrogenous compounds, having an electrical conductivity of at least < 0,5 mS/m (at 25 °C).

5.1 Kjeldahl tablets.

5.1.1 5 g/tablet containing 100 parts K₂SO₄ to 1 part selenium.

or, in alternative,

5.1.2 5 g of pure K₂SO₄ in powder (recommended).

5.2 Sulfuric acid, concentrated (mass concentration ρ₂₀ = 1,84 g/ml).

5.3 Sodium hydroxide solution, NaOH, mass fraction of 30 %.

5.4 Sulfuric acid standard solution, amount-of-substance concentration c = 0,05 mol/l (0,10 N/l), to use for the blank test in the determination of total nitrogen in urea only.

5.5 Sulfuric acid standard solution, c = 0,25 mol/l (0,5 N/l).

5.6 Sulfuric acid standard solution, c = 0,5 mol/l (1,0 N/l).

5.7 Sodium or potassium hydroxide standard solution, carbonate free, c = 0,1 mol/l, to use for the blank test in the determination of total nitrogen in urea only.

5.8 Sodium or potassium hydroxide standard solution, carbonate free, c = 0,5 mol/l.

5.9 Sodium or potassium hydroxide standard solution, carbonate free, c = 1,0 mol/l.

5.10 Indicator for ammonia nitrogen, ready for use.

5.11 Anti-bump granules, for example pumice stone, washed in hydrochloric acid and calcined.

5.12 Urea, analytical grade.

5.13 Melamine, analytical grade.

6.1 Distillation apparatus, consisting of a round-bottomed flask of suitable capacity connected to a condenser by means of a splash head.

The equipment is made of borosilicate glass.

NOTE The different types of equipment recommended for this determination are reproduced showing all the features of construction in Figures 1, 2, 3, and 4.

Automatic distillation and titration apparatus may be used as well provided that the results are statistically equivalent.

Dimensions in millimetres

Key

1 round-bottomed, long-necked flask of 1 000 ml capacity

2 distillation tube with a splash head, connected to the condenser by means of a spherical joint (No 18) (the spherical joint for the connection to the condenser may be replaced by an appropriate rubber connection)

3 funnel with a polytetrafluoroethylene (PTFE) tap (6) for the addition of sodium hydroxide

4 six-bulb condenser with spherical joint (No 18) at the entrance, and joined at the issue to a glass extension tube by means of a small rubber connection (when the connection to the distillation tube is effected by means of a rubber tube, the spherical joint may be replaced by a suitable rubber bung)

5 500 ml flask in which the distillate is collected

6 PTFE-tap (the tap may likewise be replaced by a rubber connection with a clip)

Figure 1 — Distillation apparatus 1

Dimensions in millimetres

Key

1 round-bottomed, short-necked flask of 1 000 ml capacity with a spherical joint (No 35)

2 distillation tube with a splash head, equipped with a spherical joint (No 35) at the entrance and a spherical joint (No 18) at the issue, connected at the side to a funnel with a polytetrafluoroethylene (PTFE) tap (6) for the addition of sodium hydroxide

3 six-bulb condenser with a spherical joint (No 18) at the entrance and joined at the issue to a glass extension tube by means of a small rubber connection

4 500 ml flask in which the distillate is collected

5 PTFE-tap

a enlarged description

Figure 2 — Distillation apparatus 2

Dimensions in millimetres

Key

1 round-bottomed, long-necked flask of 750 ml or 1 000 ml capacity with, a bell mouth

2 distillation tube with a splash head and a spherical joint (No 18) at the issue

3 elbow tube with a spherical joint (No 18) at the entrance, and a drip cone (the connection to the distillation tube may be effected by means of a rubber tube instead of a spherical joint)

4 six-bulb condenser joined at the issue to a glass extension tube by means of a small rubber connection

5 500 ml flask in which the distillate is collected

Figure 3 — Distillation apparatus 3

Dimensions in millimetres

Key

1 round-bottomed, long-necked flask of 1 000 ml capacity with a bell mouth

2 distillation tube with a splash head and a spherical joint (No 18), at the issue, connected at the side to a funnel with a polytetrafluoroethylene (PTFE) tap (5) for the addition of sodium hydroxide (a suitable rubber bung may be used instead of the spherical joint

3 six-bulb condenser with a spherical joint (No 18) at the entrance, joined at the issue, by a rubber connection, to a glass extension tube (when the connection to the distillation tube is effected by means of a rubber tube, the spherical joint may be replaced by a suitable rubber bung)

4 500 ml flask for the collection of the distillate

5 PTFE-tap (the tap may be replaced by a rubber connection with an appropriate clip)

Figure 4 — Distillation apparatus 4

6.2 Graduated Erlenmeyer flask, capacity 400 or 500 ml.

6.3 25 ml burettes, with a precision of 0,03 ml and a division of 0,05 ml (class AS).

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.

Sample preparation shall be carried out in accordance with EN 1482‑2.

Weigh to the nearest 0,001 g about 500 mg of the prepared sample and transfer with 10 ml demineralized water to a 800 ml Kjeldahl flask. Add, while gently swirling 30 ml sulfuric acid (5.2) and 1 Kjeldahl tablet (5.1.1).

Digestion step

Put the Kjeldahl flask in a fume cupboard. Place on a heating device and heat until boiling, with an input that is required to bring 250 ml of water at 25 °C to a “rolling boil” in 20 min to 30 min.

Continue to heat the flask and contents for approximately 1 h, until dense white fumes of sulfuric acid are escaping for at least 15 min. Allow the flask to cool to 25 °C.

Distillation step

Measure into a 500 ml Erlenmeyer receiving flask 30,00 ml of the 0,5 mol/l sulfuric acid solution (5.6). Add 270 ml water and add four or five drops of the indicator solution (5.10) and place the Erlenmeyer flask in such a way that the end of the delivery tube is at least 3 cm below the surface of the liquid. Add 250 ml water to the Kjeldahl flask and several grains of pumice stone (5.11) in order to control the boiling.

Assemble the distillation apparatus and taking care to avoid any loss of ammonia, add to the contents of the Kjeldahl flask carefully 120 ml of the sodium hydroxide solution (5.3). Agitate the flask to thoroughly mix the contents. Apply heat increasing the rate of heating progressively until finally the contents of the flask are boiling briskly.

Most of the ammonia is expelled within 15 min. Continue the distillation until 150 ml of distillate has been collected. Then lower the Erlenmeyer flask receiver so that the end of the delivery tube is out of the liquid and continue the distillation for a few more minutes. Rinse the outside of the delivery tube with a small amount of water into the Erlenmeyer flask. Back titrate the excess of acid with the 1,0 mol/l sodium hydroxide solution (5.9) to the neutral colour of the indicator (5.10).

At the same time as the determination carry out a blank test, using the same apparatus and the same quantities of all the reagents and water, but omitting the test portion and using 20,00 ml of the 0,05 mol/l sulfuric acid solution (5.4) and back titrating with the 0,1 mol/l sodium hydroxide solution (5.7).

Before carrying out the analysis, check that the apparatus is working properly and that the correct application of the method is used, using an aliquot part of a freshly prepared solution of urea (5.12).

Weigh to the nearest 0,000 1 g about 300 mg of the prepared sample and transfer with 50 ml demineralized water to a suitable Kjeldahl flask, depending to the distillation apparatus. Add 1 Kjeldahl tablet (5.1.1) or, in alternative, 5 g of potassium sulphate (5.1.2) and add, while gently swirling, 30 ml sulfuric acid (5.2).

Digestion step

Put the Kjeldahl flask in a fume cupboard. Place on a heating device and heat gradually first until boiling, then until dense white fumes of sulfuric acid are escaping. A recommended ramp is the following: about 200 °C for 1 h, about 300 °C for 0,5 h and about 400 °C for 0,75 h.

Allow the flask to cool to 25 °C.

Distillation step

Measure with the burette (6.3) into a graduated Erlenmeyer receiving flask (6.2) 25,00 ml of the sulfuric acid solution (5.5) and add 25 ml of water.

Add fifteen drops of the indicator solution (5.10) and place the graduated Erlenmeyer flask (6.2) in such a way that the end of the delivery tube is 1 cm below the surface of the liquid. Add a suitable quantity of water to the Kjeldahl flask and several grains of pumice stone (5.11) in order to control the boiling.

Assemble the distillation apparatus taking care to avoid any loss of ammonia. If the distillation apparatus is automatic, the water is automatically added.

Add to the contents of the Kjeldahl flask carefully, manually or automatically, 120 ml of the sodium hydroxide solution (5.3). Apply heat increasing the rate of heating progressively until finally the contents of the flask are boiling briskly.

Most of the ammonia is expelled within 15 min. Continue the distillation until a total of 300 ml of distillate has been collected. Rinse the outside of the delivery tube with a small amount of water into the Erlenmeyer flask. Back titrate the excess of acid with sodium or potassium hydroxide standard solution (5.8) to the green colour of the indicator (5.10).

At the same time as the determination carry out a blank test, using the same apparatus and the same quantities of all the reagents and water, but omitting the test portion.

To check that the apparatus is working properly and that the correct application of the method is used, perform two analysis simultaneously using melamine (5.13) as standard.

Express the result of the analysis as a percentage of nitrogen (N) contained in the fertilizer as received for analysis.

Calculate the mass fraction of total nitrogen, w_N in percent, using the following Formula:

(1)

where

30 is the volume, in ml of the 0,5 mol/l sulfuric acid solution (5.6);

20 is the volume, in ml of the 0,05 mol/l sulfuric acid solution (5.4);

V₁ is the volume, in ml of the 1,0 mol/l sodium hydroxide solution (5.9) used for the determination;

V₂ is the volume, in ml of the 0,1 mol/l sodium hydroxide solution (5.7) used for the blank test;

t₁ is the titre of H₂SO₄ 0,5 mol/l;

t₂ is the titre of NaOH 1,0 mol/l;

t₃ is the titre of H₂SO₄ 0,05 mol/l;

t₄ is the titre of NaOH 0,1 mol/l;

m is the mass, in mg, of the sample taken for the determination.

Express the result of the analysis as a percentage of total nitrogen (N) contained in the fertilizer as received for analysis.

Calculate the mass fraction of total nitrogen w_N, in percent, using the following formula:

(2)

where

V₁ is the volume of the 0,5 mol/l sodium or potassium hydroxide standard solution (5.6) used for the determination, in ml;

V₂ is the volume of the 0,5 mol/l sodium or potassium hydroxide standard solution (5.6) used for the blank test, in ml;

m is the mass, of the sample taken for the determination, in mg.

An inter-laboratory study was carried out in 2004 with 19 laboratories participating and one sample of urea. This test yielded the data given in Annex A. Repeatability and reproducibility were calculated according to ISO 5725‑1.

The values derived from this inter-laboratory test might not be applicable to concentration ranges and matrices other than those given in Annex A.

The absolute difference between two independent single test results, obtained with 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 exceed the values of r given in Table 1.

The absolute difference between two single test results, obtained with the same method on identical test material in different laboratories by different operators using different equipment, will in no more than 5 % of the cases exceed the values of R given in Table 1.

Table 1 — Mean value, repeatability and reproducibility limit for Urea

Details of inter-laboratory studies on the precision of the method are summarized in Annex B. Repeatability and reproducibility were calculated according to ISO 5725‑1 and ISO 5725‑2.

It is possible that the values derived from this study are not applicable to concentration ranges and matrices other than those given.

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 2.

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 2.

Table 2 — Mean values, repeatability and reproducibility limits for liquid and solid methylene-urea

The test report shall contain at least the following information:

a) all information necessary for the complete identification of the sample;

b) test method used with reference to this document, including its year of publication;

c) test results obtained expressed as the percentage mass fraction of total nitrogen in the fertilizer;

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 that occurred when performing the method which might have influenced the test result(s).

1. 
   (informative)
   
   Results of the inter-laboratory tests

The precision of the method was established in 2004 by Working Group 7 “Chemical analysis” of CEN/TC 260 “Fertilizers and liming materials” in an inter-laboratory test evaluated in accordance with ISO 5725‑1. The statistical results are given in Table A.1.

Table A.1 — Statistical results of the inter-laboratory test for urea

1. 
   (informative)
   
   Results of the inter-laboratory study
   1. Inter-laboratory study

The precision of the method has been determined in the year 2025 in an inter-laboratory study with 10 laboratories participating and carried out on 2 samples of inorganic fertilizers.

The statistical results are given in Table B.1.

The statistical results for the samples are given in Table B.1.

• 1. Statistical results for the determination of total nitrogen according to this document

Table B.1 — Statistical results for the determination of total nitrogen in inorganic fertilizers

Bibliography

[1] EN 1482‑1, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part 1: General sampling provisions

[2] ISO 5725‑1, Accuracy (trueness and precision) of measurement methods and results — Part 1: General principles and definitions

[3] 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

1. A revision is under preparation. Stage at the time of preparation: prEN 12944-1:2026 ↑

2. A revision is under preparation. Stage at the time of preparation: prEN 12944-2:2026 ↑