prEN 17771

• Abstract:

  This document specifies a method for the determination of the total nitrogen content and the content of ammoniacal, nitric, ureic and organic nitrogen in organic and organo-mineral fertilizers.; This document is applicable to fertilizing product blends, where the blend is a mix of at least two of the following components: fertilizers, liming materials, soil improvers, biostimulants and where the following category organic fertilizers, organo-mineral fertilizers is the highest % in the blend by mass or volume, or in the case of liquid form by dry mass. If the organic fertilizer or the organo-mineral fertilizer is not the highest % in the blend, the European Standard for the highest % of the blend applies. In case a fertilizing product blend is composed of components in equal quantity, the user decides which standard to apply.; This document is applicable to products that at least contain a total nitrogen content of 1 % by mass. In case of fertilizing product blends, it is unattainable to ascertain the origin of the measured nitrogen with respect to the specific component.; NOTE 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.

• Status: Not Published
• Publication Date: 12-Sep-2027
• ICS: 65.080 - Fertilizers
• Technical Committee: CEN/TC 260 - Fertilizers and liming materials
• Drafting Committee: CEN/TC 260/WG 8 - Organic and organo-mineral fertilizers
• Current Stage: 4010 - Start of draft translation - Enquiry
• Start Date: 15-Jun-2026
• Completion Date: 11-Jun-2026
• Directive: Harmonized Standard2019/1009 - 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: oSIST prEN 17771:2026 - Organic and organo-mineral fertilizers - Determination of the nitrogen content

• Revises: CEN/TS 17771:2022 - Organic and organo-mineral fertilizers - Determination of the nitrogen content
• Effective Date: 11-Jun-2025

Overview

prEN 17771: Organic and organo-mineral fertilizers - Determination of the nitrogen content is a European draft standard developed by CEN/TC 260 “Fertilizers and liming materials”. This document outlines a standardized method for determining the total nitrogen content and the specific forms of nitrogen-including ammoniacal, nitric, ureic, and organic nitrogen-in organic and organo-mineral fertilizers. It is applicable to both individual fertilizer products and blends containing organic and organo-mineral fertilizers as the predominant component by mass or volume, aligning with EU regulatory requirements for fertilizer products.

Key Topics

• Scope of Application
  • Relevant for organic fertilizers, organo-mineral fertilizers, and their blends
  • Applies when organic or organo-mineral fertilizers make up the largest proportion by mass or volume in a blend
  • Minimum total nitrogen content of 1% by mass required
• Nitrogen Fraction Determination
  • Quantitative methods to distinguish between ammoniacal, nitric, ureic, and organic nitrogen forms
  • Considers matrix interactions in blends, ensuring reliable measurements
• Analytical Pathways
  • Four distinct analysis methods based on the modified Kjeldahl process
  • Includes digestion, distillation, and titration steps to ensure precise nitrogen determination
• Quality and Robustness
  • Harmonized methods validated through inter-laboratory testing
  • Methods robust across a broad range of product compositions, with awareness of possible matrix effects

Applications

• Fertilizer Quality Control
  • Ensures the accurate labeling of nitrogen content in organic and organo-mineral fertilizers for regulatory compliance and market acceptance
  • Helps manufacturers and laboratories consistently meet EU requirements, particularly those outlined in Regulation (EU) 2019/1009
• Blended Fertilizing Products
  • Facilitates standard analysis of fertilizer blends, including combinations containing soil improvers, liming materials, or biostimulants
  • When organic or organo-mineral fertilizer is not the primary component, other relevant European standards apply
• Regulatory Certification
  • Required for product certification and market placement within the European Union
  • Provides traceability and consistency for product approval and audit processes
• Agricultural Testing Laboratories
  • Used by testing labs for routine analysis and reporting of fertilizer nitrogen specifications
  • Supports research, development, and comparative quality studies among fertilizer products

Related Standards

For a comprehensive approach to fertilizer sampling, definitions, and analysis, refer to the following standards:

• EN 1482-2:2024 - Fertilizers, liming materials and inhibitors - Sampling and sample preparation
• EN 12944-1:1999 - Fertilizers and liming materials - Vocabulary - General terms
• EN 12944-2:1999 - Fertilizers and liming materials - Vocabulary - Terms relating to fertilizers
• Regulation (EU) 2019/1009 - Market placement of EU fertilizing products, including requirements for organic and organo-mineral fertilizers

NOTE: For fertilizer blends with equally weighted components, users must choose the appropriate standard to apply as per prEN 17771 guidance.

Practical Value

By adhering to prEN 17771, fertilizer producers, laboratories, and regulatory bodies gain:

• Confidence in Results: Approved and validated test methods support reliable, repeatable, and reproducible results for all nitrogen forms.
• Compliance and Trade: Assures compliance with EU fertilizers legislation, strengthening market access and consumer trust.
• Versatility: Suitable for solids and liquids, individual fertilizers, and blends, making it a vital tool for diverse product portfolios.
• Transparency: Heightened transparency in fertilizer composition, supporting environmental sustainability and agronomic performance.

Keywords: organic fertilizers, organo-mineral fertilizers, nitrogen determination, nitrogen content, fertilizer blends, fertilizer testing, CEN standards, EU fertilizer regulation, nutrient analysis, laboratory standards.

SLOVENSKI STANDARD
01-september-2026
Organska in organsko-mineralna gnojila - Določanje dušika
Organic and organo-mineral fertilizers - Determination of the nitrogen content
Organische und organisch-mineralische Düngemittel - Bestimmung des
Stickstoffgehaltes
Ta slovenski standard je istoveten z: prEN 17771
ICS:
65.080 Gnojila Fertilizers
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2026
ICS 65.080 Will supersede CEN/TS 17771:2022
English Version
Organic and organo-mineral fertilizers - Determination of
the nitrogen content
Organische und organisch-mineralische Düngemittel -
Bestimmung des Stickstoffgehaltes
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 17771:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Principle . 5
5 Reagents . 7
6 Apparatus . 10
7 Sampling and sample preparation . 10
8 Procedure . 10
8.1 General. 10
8.2 Standard unit operations . 11
9 Calculation and expression of the results . 13
9.1 Calculation of the nitrogen fractions . 13
9.2 Calculation of the maximum ammonium nitrate content . 14
10 Verification of the result . 14
11 Precision . 14
11.1 Inter-laboratory study . 14
11.2 Repeatability . 15
11.3 Reproducibility . 15
12 Test report . 15
Annex A (informative) Results of the interlaboratory study . 16
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 . 22
Bibliography . 24

European foreword
This document (prEN 17771:2026) 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 17771:2022.
CEN/TS 17771:2022:
— The CEN Technical Specification has been adopted as a European Standard including the addition of
Annex ZA;
— Scope (Clause 1) updated including a clarification on fertilizing product blends;
— Normative references and Bibliography revised;
— Annex A (Results of the interlaboratory study) added;
— Annex ZA 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.
Introduction
Regulation (EU) 2019/1009 [1] lays down the rules on the making available on the market of EU
fertilizing products and the specific safety and quality requirements for the defined product function
categories (PFCs). Organic and organo-mineral fertilizers have been classified as PFC 1(A) and PFC 1(B).
This document defines test methods for the determination of the nitrogen content to be used for organic
and organo-mineral fertilizers in order to measure the compliance with the related requirement in
Regulation (EU) 2019/1009 [1].
The inter-laboratory study reflects the final statistical characteristics of the method for the determination
of the specific forms of nitrogen present in the sample.
1 Scope
This document specifies a method for the determination of the total nitrogen content and the content of
ammoniacal, nitric, ureic and organic nitrogen in organic and organo-mineral fertilizers.
This document is applicable to fertilizing product blends, where the blend is a mix of at least two of the
following components: fertilizers, liming materials, soil improvers, biostimulants and where the
following category organic fertilizers, organo-mineral fertilizers is the highest % in the blend by mass or
volume, or in the case of liquid form by dry mass. If the organic fertilizer or the organo-mineral fertilizer
is not the highest % in the blend, the European Standard for the highest % of the blend applies. In case a
fertilizing product blend is composed of components in equal quantity, the user decides which standard
to apply.
This document is applicable to products that at least contain a total nitrogen content of 1 % by mass. In
case of fertilizing product blends, it is unattainable to ascertain the origin of the measured nitrogen with
respect to the specific component.
NOTE 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.
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 1482-2:2024, Fertilizers, liming materials and inhibitors - Sampling and sample preparation - Part 2:
General sample preparation provisions
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
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 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/
4 Principle
The fertilizer sample shall be analysed according to four different analytical pathways to quantify the
different forms of nitrogen in the sample. The nitrogen content determined by the four analytical
pathways is representative for:
a) total nitrogen content;
As impacted by EN 12944-1:1999/AC:2000.
As impacted by EN 12944-2:1999/AC:2000.
b) total nitrogen content with exception of nitric nitrogen;
c) ammoniacal nitrogen content;
d) ammoniacal nitrogen and ureic nitrogen content.
The analysis results that are obtained by the determination of nitrogen according to these four pathways
shall be used to calculate the content of ammoniacal, nitric, ureic, and organic nitrogen in the sample
(see 9.1).
All four analytical pathways are based on or derived from the Kjeldahl principle. First, a pretreatment
and/or digestion shall be performed to convert the nitrogen of a certain fraction of nitrogenous
compounds to ammonia. Next, the ammoniacal nitrogen shall be distilled into a known volume and
concentration of hydrochloric acid. Finally, the ammoniacal nitrogen shall be quantified by titration of
excess amount of acid in the receiving flask with sodium hydroxide.
The procedures that shall be performed for the pretreatment, digestion and distillation depend on the
analytical pathway, as schematically shown in Figure 1.
When performing analytical pathway 1, the total nitrogen content shall be determined by a reduction
with the aid of reduced iron and stannous chloride to convert nitric nitrogen to ammonia, followed by
Kjeldahl digestion of the sample. Subsequently, the ammonia shall be distilled after addition of sodium
hydroxide.
NOTE For the determination of the total nitrogen content, the Dumas method can also be applied if it is proven
to be as accurate and precise as the Kjeldahl method.
When performing analytical pathway 2, the total nitrogen with the exception of nitric nitrogen shall be
determined by a Kjeldahl digestion with ferrous sulfate. Then, the ammonia shall be distilled after
addition of sodium hydroxide.
When performing analytical pathway 3, the ammoniacal nitrogen content shall be determined by a mild
distillation after addition of magnesium oxide.
Performing pathway 4, the ureic and ammoniacal nitrogen content shall be determined by a pretreatment
with urease. Subsequently, the ammonia shall be distilled by a mild distillation after addition of
magnesium oxide.
Figure 1 — The four analytical pathways for the determination of the different nitrogen
fractions
5 Reagents
The following reagents shall be used. All reagents should be of recognized analytical grade.
5.1 Water, with a specific conductivity not higher than 0,2 mS/m at 25 °C, free from the elements to be
determined.
5.2 Reduced iron.
Iron powder reduced by hydrogen.
5.3 Standard iodine solution (I substance concentration, c = 0,05 mol/l).
2,
5.4 Stannous chloride solution (SnCl , c = 0,532 mol/l)
For the preparation of the stannous chloride solution, the following tasks shall be performed:
— Weigh 120 g of stannous chloride dihydrate and transfer it into a 1 l volumetric flask;
— Add 400 ml concentrated hydrochloric acid (mass concentration at 20 °C, ρ = 1,18 g/ml) to the
flask;
— Bring to volume with water and shake the flask until all stannous chloride is dissolved.
The solution shall be clear and prepared immediately before use.
It is essential to check the reducing power of stannous chloride dihydrate. In order to check the reducing
power, the following steps shall be performed:
— Weigh 0,5 g of stannous chloride dihydrate and transfer it into a 50 ml volumetric flask;
— Add 2 ml concentrated hydrochloric acid (ρ = 1,18 g/ml) to the flask;
— Bring to volume with water and shake the flask until all stannous chloride is dissolved;
— Transfer the content of the volumetric flask into a glass beaker;
— Weigh 5 g of Rochelle salt (potassium sodium tartrate) and transfer into the glass beaker;
— Add sufficient quantity of sodium bicarbonate for the solution to be alkaline to litmus paper.
Titrate this solution with an iodine solution (I ) (5.3) in the presence of a starch solution as an indicator.
1 ml of the iodine solution corresponds to 0,011 28 g of stannous chloride dihydrate. At least 80 % of the
total tin present in the solution thus prepared shall be in bivalent form.
Therefore, at least 35 ml of the iodine solution should be required for the titration.
5.5 Defoaming agent
Octyl alcohol shall be used as defoaming agent, or any other non-nitrogen containing agent.
5.6 Ferrous sulfate
Crystalline ferrous sulfate heptahydrate (FeSO ·7 H O).
4 2
5.7 Sulfuric acid (c = 18 mol/l)
Concentrated sulfuric acid (H SO ), ρ = 1,84 g/ml.
2 4 20
5.8 Hydrochloric acid solution (c = 6 mol/l)
For the preparation of this hydrochloric acid solution gradually add one volume of concentrated
hydrochloric acid (ρ = 1,18 g/ml) to one volume of water.
5.9 Hydrochloric acid solution (c = 0,1 mol/l)
For the preparation of this hydrochloric acid solution, the following tasks shall be performed:
— Fill a 1 l volumetric flask about three-quarters with water;
— Add 8,5 ml of concentrated hydrochloric acid (ρ = 1,18 g/ml);
— Bring to a volume of 1 l.
5.10 Sodium hydroxide solution (c = 7,5 mol/l)
For the preparation of the sodium hydroxide solution of about 30 % (mass concentration), the following
tasks shall be performed:
— Fill a 1 l flask about three-quarters with water.
— Weigh 300 g sodium hydroxide and gradually add it to the flask.
— Stir the solution until all sodium hydroxide is dissolved.
— Bring to a volume of 1 l.
5.11 Sodium hydroxide solution (c = 0,1 mol/l)
Certified standard solution of sodium hydroxide 0,1 mol/l.
5.12 Phosphate buffer (c = 0,15 mol/l, pH 6,8)
— Weigh 12,60 g NaH PO and transfer into a 1 l volumetric flask;
2 4
— Weigh 6,38 g Na HPO ·2 H O and transfer into the 1 l volumetric flask;
2 4 2
— Bring to volume with water and shake until all sodium phosphate is dissolved;
— Adjust the pH to 6,8 by adding hydrochloric acid solution (5.9) or sodium hydroxide (5.11).
5.13 Urease solution
For the preparation of the urease solution the following tasks shall be performed:
— Suspend 5 g of active urease, with an activity of at least 5 U/mg in 1 l of phosphate buffer pH 6,8
(5.12).
— Adjust the pH to 6,8 by adding hydrochloric acid (5.9) or sodium hydroxide solution (5.11).
5.14 Catalyst
A mixture of: (a) 10 g of potassium sulfate (K SO ) and 0,3 g of copper oxide (CuO) or (b) 10 g of
2 4
potassium sulfate and 1 g of copper sulfate pentahydrate (CuSO ·5H O) shall be used as catalyst for the
4 2
digestion, possibly in the form of tablets containing similar amount of the chemicals mentioned.
5.15 Indicator solutions
The following tasks shall be performed to prepare the indicator solutions:
5.15.1 Indicator solution I
— Weigh 1 g of methyl red and transfer it into a 1 l volumetric flask;
— Add 0,5 ml of sodium hydroxide solution 7,5 mol/l (5.10);
— Bring to volume with water and shake the flask until all methyl red is dissolved.
5.15.2 Indicator solution II
— Weigh 1 g of methylene blue and transfer into a 1 l volumetric flask;
— Bring to volume with water and shake the flask until all methylene blue is dissolved.
5.15.3 Combined indicator solution
— Mix one volume of indicator solution I (5.15.1) with two volumes of indicator solution II (5.15.2).
The combined pH indicator (5.15.3) changes colour from violet to green between pH 4,4 and pH 6,2 and
is grey at the equivalence point (pH 5,2). A quantity of 0,5 ml (10 drops) of this indicator solution should
be used.
5.15.4 Methyl red indicator solution
— Weigh 1 g of methyl red and transfer it into a 1 l volumetric flask;
— Add 0,5 l of ethanol;
— Bring to volume with water and shake the flask until all methyl red is dissolved;
— Filter the solution if necessary.
This pH indicator changes colour from red to yellow between pH 4,4 and pH 6,2 and may be used instead
of that described in 5.15.3. A quantity of four or five drops of this indicator solution should be used.
5.15.5 Phenolphthalein solution
— Weigh 1 g phenolphthalein and transfer it into a 100 ml volumetric flask;
— Add 50 ml of ethanol;
— Bring to volume with water and shake the flask until all phenolphthalein is dissolved.
This pH indicator changes from colourless to pink between pH 8,3 and pH 10,0.
5.16 Magnesium oxide
5.17 Indicator paper
5.18 Potassium thiocyanate
5.19 Potassium nitrate.
5.20 Ammonium sulfate
5.21 Urea
5.22 Bovine serum albumin
Lyophilized, crystalized bovine serum albumin.
6 Apparatus
Disposable equipment is acceptable in the same way as reusable glassware if the specifications are
similar. Ordinary laboratory equipment, and:
6.1 Analytical balance, capable of reading to the nearest 0,001 g or better.
6.2 Common laboratory glass ware, e.g. volumetric flasks.
6.3 Boiling chips.
6.4 pH-meter, with glass electrode.
6.5 Automated apparatuses.
In order to facilitate automatization, commercially available automated apparatuses can be used if equal
reaction conditions (e.g. reagents, temperature) are attained. Furthermore, the operations shall comply
with the necessary safety precautions, including the precautions that are required for the avoidance of
ammonia loss. If automated equipment is used then it shall be proven to be as accurate and precise as the
method here described.
7 Sampling and sample preparation
Sampling is not part of the method specified in this document. Recommended sampling methods are
given in EN 1482-1 [5] and/or EN 1482-3 [6]. It is important that the laboratory receives a sample that is
representative of the product under consideration and the given analysis, respectively. The sample
should not have been damaged or changed during transport or storage.
Sample preparation shall be carried out in accordance with EN 1482-2:2024.
Nitrogen might be lost due to ammonia volatilization throughout the procedure, depending mainly on pH
and temperature. When needed appropriate precautions shall be taken.
8 Procedure
8.1 General
The fertilizer sample shall be analysed according to four different analytical pathways to quantify the
different forms of nitrogen that are present in the sample. Table 1 shows the standard unit operations
that shall be carried out to obtain the results for the four analytical pathways. The results of the four
analytical pathways shall be used to determine total nitrogen content and the contribution of the
individual nitrogen fractions.
Table 1 — Unit operations
Pathway Pretreatment Digestion Distillation Titration
1 8.2 a) 8.2 e) 8.2 f) 8.2 g)
(Method A: Distillation)
2 8.2 b) 8.2 e) 8.2 f) 8.2 g)
(Method A: Distillation)
3 8.2 c) - 8.2 f) 8.2 g)
(Method B: Mild distillation)
4 8.2 d) - 8.2 f) 8.2 g)
(Method B: Mild distillation)
Be sure to take into account the safety of the fertilizing product to avoid harm due to explosions, caking,
foaming, bumping, toxic gases, toxic compounds for people.
8.2 Standard unit operations
The following tasks shall be performed:
a) Pretreatment for the determination of total nitrogen by reduction of nitric nitrogen to
ammoniacal nitrogen
— Weigh to the nearest 0,001 g an amount of the sample not exceeding 40 mg of nitrogen or a maximum
of 650 mg organic matter;
— Transfer the sample into a Kjeldahl tube e.g. 250 ml;
— Add 0,5 g of reduced iron (5.2) and 40 ml of stannous chloride solution (5.4);
— Shake the flask and leave it to stand for 0,5 h. During this half hour, stir a few times. If necessary, add
a few drops of defoaming agent (5.5);
— Proceed with the digestion described in 8.2 e).
b) Pretreatment for the determination of total nitrogen with exception of nitric nitrogen
— Weigh to the nearest 0,001 g an amount of the sample not exceeding 40 mg of nitrogen or a maximum
of 650 mg organic matter;
— Mix the sample in a Kjeldahl tube e.g. 250 ml with 50 ml water;
— Add 5 g of ferrous sulfate (5.6) and 5 ml of sulfuric acid (5.7);
— Proceed with the digestion described in 8.2 e).
c) Pretreatment for the determination of ammoniacal nitrogen content
— Weigh to the nearest 0,001 g an amount of the sample containing a maximum of 40 mg of ammoniacal
nitrogen;
— Mix the sample in a distillation flask with water;
— Directly after proceed with the mild version of the distillation described in 8.2 f).
If the distillation cannot be carried out immediately afterwards, add 5 ml of hydrochloric acid solution
(5.8).
d) Pretreatment using the urease method
— Weigh to the nearest 0,001 g an amount of the sample containing a
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