prEN 17776

SLOVENSKI STANDARD
01-marec-2026
Organska in organsko-mineralna gnojila - Določanje celotnega organskega ogljika
(TOC) s suhim sežigom
Organic and organo-mineral fertilizers - Determination of the total organic carbon (TOC)
content by dry combustion
Organische und organisch-mineralische Düngemittel - Bestimmung des Gehalts an
gesamtem organischem Kohlenstoff (TOC) durch trockene Verbrennung
Engrais organiques et organo-minéraux - Détermination de la teneur en carbone
organique total (COT) par combustion sèche
Ta slovenski standard je istoveten z: prEN 17776
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
January 2026
ICS 65.080 Will supersede CEN/TS 17776:2022
English Version
Organic and organo-mineral fertilizers - Determination of
the total organic carbon (TOC) content by dry combustion
Engrais organiques et organo-minéraux - Organische und organisch-mineralische Düngemittel -
Détermination de la teneur en carbone organique total Bestimmung des Gehalts an gesamtem organischem
(COT) par combustion sèche Kohlenstoff (TOC) durch trockene Verbrennung
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 17776:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Principle . 7
4.1 Method A (direct method): . 7
4.2 Method B (indirect method): . 7
5 Applicability . 7
6 Interferences . 7
7 Sampling and sample preparation . 8
8 Reagents . 8
9 Apparatus . 9
10 Procedure . 9
10.1 General. 9
10.2 Method A - determination of the TOC – direct method . 9
10.2.1 Preparation of solid samples . 9
10.2.2 Preparation of liquid samples . 10
10.2.3 Removal of inorganic carbon and determination of the TOC . 10
10.2.4 Calibration . 11
10.2.5 Control measurements . 11
10.3 Method B – determination TC and TIC - indirect method . 12
10.3.1 Determination of the TC . 12
10.3.2 Calibration TC. 12
10.3.3 Determination of the TIC . 12
10.3.4 Calibration TIC . 12
11 Calculation and expression of results . 13
11.1 Method A calculation . 13
11.2 Method B calculation . 14
12 Precision . 15
12.1 Inter-laboratory study . 15
12.2 Repeatability . 15
12.3 Reproducibility . 15
13 Test report . 15
Annex A (informative) Example of operational information . 17
Annex B (informative) Results of the interlaboratory study . 19
B.1 Inter-laboratory study . 19
B.2 Statistical results for the determination of total organic carbon (TOC) content by dry
combustion . 19
Bibliography . 21

European foreword
This document (prEN 17776:2026) 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 17776:2022.
Compared to the previous edition, prEN 17776:2025 includes the following significant technical changes:
— The CEN Technical Specification has been adopted as a European Standard;
— Introduction revised;
— Scope (Clause 1) updated including clarifications on fertilizing product blends;
— Terms and definitions revised;
— Method for indirect determination of organic carbon added in 10.3;
— Principle of indirect method added in Paragraph 4.2;
— Reagents revised with respect to changes in the text;
— Formula for indirect method added in 11.2;
— Clause 12 (Precision) added;
— Annex B (Results of the inter-laboratory study) added.
— Bibliography revised.
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.
Introduction
An EU fertilizing product consists solely of component materials complying with the requirements for
one or more of the component material categories (CMCs), as specified in the Regulation (EU) 2019/1009
[1]. This regulation lays down the rules on the making available on the market of EU fertilizing products
and the specific safety and quality requirements for the CMCs.
By-products within the meaning of Directive 2008/98/EC have been classified as CMC 11 and recovered
high purity materials as CMC 15, in Regulation (EU) 2019/1009 [1].
The method described in this document is based on the standard for determining organic carbon in
sludges, biowaste, soil, and other solid matrices (EN 15936 [3]).
WARNING — Persons using this document should be familiar with usual 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 Scope
This document specifies a method for the determination of total organic carbon (TOC) by elemental
analysis using dry combustion. The method is applicable to organic and organo-mineral fertilizers
containing more than 1 g carbon per kg of dry matter (0,1 %), with the exclusion of organo-mineral
fertilizers containing urea-formaldehyde polymers or urea as long as there is no method available to
assess carbon in urea-formaldehyde polymers or urea.
This document is applicable to the component materials “by-products”, or “recovered high-purity
materials”, when used as components of fertilizing products, as well as the fertilizing products blends
where a blend is a mix of at least two of the following components: fertilizers, liming materials, soil
improvers, growing media, inhibitors, plant 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. 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.
This document is applicable and validated for several types of matrices as indicated in Annex B.
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.
CEN/TS 17771, Organic and organo-mineral fertilizers — Determination of the nitrogen content
prEN 17773 , Organic and organo-mineral fertilizers — Determination of the dry matter content
EN 17864, Inorganic fertilizers — Determination of nitrogen content in IBDU (isobutylidenediurea) and
CDU (crotonylidenediurea)
EN 12944-1, Fertilizers and liming materials — Vocabulary — Part 1: General terms
EN 12944-2, Fertilizers and liming materials — Vocabulary — Part 2: Terms relating to fertilizers
EN 1482-2, Fertilizers, liming materials and inhibitors — Sampling and sample preparation — Part 2:
General sample preparation provisions
3 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 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/

Under preparation.
3.1
total organic carbon
TOC
quantity of carbon that is converted into carbon dioxide by combustion and which is not liberated as
carbon dioxide by acid treatment
3.2
total inorganic carbon
TIC
quantity of carbon that is liberated as carbon dioxide by acid treatment
3.3
total carbon
TC
quantity of carbon present in the sample in the form of organic, inorganic and elemental carbon
Note 1 to entry: Carbon derived from urea and polymers containing urea are not considered as organic in this
document.
4 Principle
4.1 Method A (direct method):
The carbon dioxide released by the following combustion in an oxygen containing gas flow free of carbon
dioxide, is measured by infrared spectrometry, thermal conductivity detection, or by the detector
provided by the equipment used. To ensure complete combustion, catalysts and/or modifiers can be
used. The released amount of carbon dioxide indicates the TOC.
The carbonates present in the sample shall be previously removed by treating the sample with acid. The
carbon dioxide released by the following combustion step indicates the TOC directly.
4.2 Method B (indirect method):
TOC is obtained by the difference between the results of the measurements of TC and TIC. The total
carbon (TC) present in the sample is converted into carbon dioxide by combustion in an oxygen
containing gas flow free of carbon dioxide. To ensure complete combustion, catalysts and/or modifiers
can be used. The released amount of carbon dioxide is measured e.g. by infrared spectrometry, thermal
conductivity detection, or other suitable techniques.
The TIC is determined separately from another sub-sample by means of acidification and purging of the
released carbon dioxide. The carbon dioxide shall be measured by one of the techniques mentioned
above.
5 Applicability
The methods 4.1 and 4.2 are applicable to organic and organo-mineral fertilizers both solid and liquid.
The method 4.1 is not selective, because combustion occurs for both organic and inorganic carbon.
6 Interferences
In the case of experience with samples containing high amounts of carbonates (e.g. carbonates to TOC
ratio higher than 10) the operator shall take care to correctly eliminate all the carbonates to make sure
to produce reliable TOC results.
When present, carbon from urea and urea-condensates carbides is determined as organic carbon using
the method described in this document. An interpretation of the measured value may therefore be
problematic in cases where the sample contains relevant levels of the above-mentioned components. If
needed, these components shall be determined separately by means of a suitable validated method and
be recorded in the test report.
Carbon from urea and urea-condensates (crotonyliden diurea, CDU and isobutyliden diurea, IBDU),
determined separately using CEN/TS 17771 and EN 17864 shall be subtracted. If this is done this shall
be reported by the laboratory.
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 in EN 1482-3 [6].
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. Grinding of the laboratory sample
is recommended for homogeneity reasons. The sample shall then pass through a sieve of 0,5 mm.
8 Reagents
8.1 Water, with a specific conductivity not higher than 0,2 mS/m at 25 °C, free from the elements to be
determined. All reagents shall be of recognized analytical grade.
8.2 Potassium hydrogen phthalate, C H O K.
8 5 4
8.3 Acetanilide, C H NO.
8 9
8.4 Atropine, C H NO .
17 23 3
8.5 Ethylenediaminetetraacetic acid, (EDTA), C H N O .
10 16 2 8
8.6 Diethylenetriaminepentaacetic acid, (DTPA), C H N O .
14 23 3 10
8.7 Sodium salicylate, C H O Na.
7 5 3
8.8 Tetrasodium ethylenediamine tetraacetate-tetra-hydrate, Na -EDTA ⋅ 4H O (C H N O Na ⋅
4 2 10 12 2 8 4
4H O), heated at 80 °C for 2 h.
Other forms of Na -EDTA hydrates may be used if the water content is exactly known. In these cases, the
composition of the control mixtures shall be recalculated accordingly (see also 8.12).
8.9 Aluminium oxide, Al O , neutral, granular size < 200 µm, annealed at 600 °C.
2 3
8.10 Calcium carbonate, CaCO .
8.11 Sodium carbonate, Na CO , anhydrous.
2 3
8.12 Control mixture
Control mixture prepared from sodium salicylate (8.7), calcium carbonate (8.10), Na -EDTA ⋅ 4H O (8.8)
4 2
and aluminium oxide (8.9) in a mass ratio of 1,00 : 4,36 : 1,97 : 8,40.
The mixture shall be homogenized. It should contain 33,3 g/kg total inorganic carbon and 66,6 g/kg TOC
(e.g. 6,36 g of sodium salicylate, 27,78 g of calcium carbonate, 12,50 g of Na -EDTA ⋅ 4H O, 53,36 g of
4 2
aluminium oxide). ®
8.13 Inert absorbent material for determination on fluid samples (such as Chromosorb ).
8.14 Non-oxidizing mineral acid used for carbon dioxide expulsion, e.g. phosphoric acid H PO
3 4
(w = 85 %).
NOTE Due to possible corrosion by hydrochloric acid, phosphoric acid is preferred.
8.15 Carrier gas, e.g. synthetic air, nitrogen, helium, oxygen or argon, free of carbon dioxide and organic
impurities in accordance with the manufacturer's instructions.
9 Apparatus
9.1 Analytical balance, capable of weighing to the nearest 1 mg or better.
9.2 Equipment for determination of carbon in solids, with accessories.
9.3 Crucibles, capsules or boats, made of e.g. silver, tin, ceramics or platinum.
Tin and nickel crucibles are not acid-resistant. In case of the necessity to remove inorganic carbon (see
10.2.3), silver or ceramics vessels shall be used.
9.4 Pasteur pipettes.
9.5 Drying system, thermostatically controlled and capable of maintaining temperature of
(105 ± 2) °C.
9.6 Desiccator, with an active drying agent such as silica gel.
9.7 Evaporating dish or crucible, temperature tolerant laboratory vessel with a temperature
resistance of at least 110 °C. Suitable materials are metallic, ceramic, borosilicate glass or quartz,
porcelain, etc.
9.8 Purging unit for TIC determination, for Method B only.
10 Procedure
10.1 General
The mass of the test portion should be as la
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