CEN/TC 411

Date: 2025-09-26

prEN 16640:2025

Secretariat: SIS

Bio-based products — Bio-based carbon content — Determination of the bio-based carbon content using the radiocarbon method

Biobasierte Produkte — Gehalt an biobasiertem Kohlenstoff — Bestimmung des Gehalts an biobasiertem Kohlenstoff mittels Radiokarbonmethode

Produits biosourcés — Teneur en carbone biosourcé — Détermination de la teneur en carbone biosourcé par la méthode au radiocarbone

CCMC will prepare and attach the official title page.

Contents Page

European foreword 3

Introduction 4

1 Scope 5

2 Normative references 5

3 Terms and definitions 5

4 Symbols and abbreviated terms 6

5 Principle 8

6 Determination of the ¹⁴C content 11

6.1 General 11

6.2 Principle 11

6.3 Sampling 12

6.4 Procedure for the conversion of the carbon present in the sample to a suitable sample for ¹⁴C determination 12

6.5 Measurements 12

7 Calculation of the bio-based carbon content 12

7.1 General 12

7.2 Reference value for 100 % bio-based carbon 13

7.3 Calculation method 13

7.3.1 Calculation of the bio-based carbon content by dry mass x_B 13

7.3.2 Calculation of the bio-based carbon content x^TC_B as a fraction of TC 14

7.3.3 Examples 14

7.3.4 Examples of calculations x^TC_B 15

8 Performance characteristics 15

9 Test report 15

Annex A (informative) Procedures for sampling of products 17

Annex B (normative) Procedure for the conversion of the carbon present in the sample to a suitable sample for ¹⁴C determination 18

Annex C (normative) Method A - Liquid scintillation-counter method (LSC) 23

Annex D (normative) Method B - Accelerator mass spectrometry (AMS) 26

Annex E (normative) Method C - Saturated-absorption cavity ring-down (SCAR) 28

Annex F (informative) Performance characteristics 31

Annex G (informative) Synthesis report on AMS - SCAR intercomparison measurements 34

Bibliography 39

European foreword

This document (prEN 16640:2025) has been prepared by Technical Committee CEN/TC 411 “Bio-based products”, the secretariat of which is held by SIS.

This document is currently submitted to the CEN Enquiry.

This document will supersede EN 16640:2017.

prEN 16640:2025 includes the following significant technical changes with respect to EN 16640:2017:

— The saturated-absorption cavity ring-down spectroscopy (SCAR) method has been added. This includes an annex comparing the SCAR method to the accelerator mass spectrometry (AMS) method

— The beta-ionization (BI) method has been removed.

— Reference value for 100 % bio-based carbon is now taken from an ASTM standard.

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

Bio-based products from forestry and agriculture have a long history of application, such as paper, board and various chemicals and materials. The last decades have seen the emergence of new bio-based products in the market. Some of the reasons for the increased interest lie in the benefits of bio-based products in relation to the depletion of fossil resources and climate change. Bio-based products can also provide additional product functionalities. These developments have triggered a wave of innovation with the development of knowledge and technologies allowing new transformation processes and product development.

Acknowledging the need for common standards for bio-based products, the European Commission issued mandate M/492^[1], resulting in a series of standards developed by CEN/TC 411 during 2012-2017, with a focus on bio-based products other than food, feed and biomass for energy applications. The previous version of this document (EN 16640:2017) was developed under the mandate, but this revised version was developed after the expiration of the mandate, upon the initiative of the stakeholders in CEN/TC 411.

The standards of CEN/TC 411 “Bio-based products” provide a common basis on the following aspects:

— common terminology;

— bio-based content determination;

— life cycle assessment (LCA);

— sustainability aspects; and

— declaration tools.

It is important to understand what the term bio-based product covers and how it is being used. The term ‘bio-based’ means 'derived from biomass'. Bio-based products (bottles, insulation materials, wood and wood products, paper, solvents, chemical intermediates, composite materials, etc.) are products which are wholly or partly derived from biomass. It is essential to characterize the amount of biomass contained in the product by, for instance, its bio-based content or bio-based carbon content.

The bio-based content of a product does not provide information on its environmental impact or sustainability, which can be assessed through LCA and sustainability criteria. In addition, transparent and unambiguous communication within bio-based value chains is facilitated by a harmonized framework for certification and declaration.

This document has been developed with the aim to specify the method for the determination of bio-based carbon content in bio-based products using the ¹⁴C method. This method is based on the analytical test methods used for the determination of the age of objects containing carbon.

This document provides the reference test methods for laboratories, producers, suppliers and purchasers of bio-based product materials and products. It can be also useful for authorities and inspection organizations.

Part of the research leading to the previous version of this document has been performed under the European Union Seventh Framework Programme (see https://www.biobasedeconomy.eu/research/kbbpps/).

The analytical test methods specified in this document are compatible with those described in ASTM D6866.

This document specifies a method for the determination of the bio-based carbon content in products, based on the ¹⁴C content measurement.

This document also specifies three test methods to be used for the determination of the ¹⁴C content from which the bio-based carbon content is calculated:

— method A: Liquid scintillation-counter (LSC);

— method B: Accelerator mass spectrometry (AMS); and

— method C: Saturated-absorption cavity ring-down (SCAR) spectroscopy.

The bio-based carbon content is expressed by a fraction of sample mass or as a fraction of the total carbon content. This calculation method is applicable to any product containing carbon, including bio-composites.

NOTE This document does not provide the methodology for the calculation of the biomass content of a sample, see EN 16785‑1 and EN 16785‑2.

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 16575, Bio-based products - Vocabulary

ASTM D6866, Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis

For the purposes of this document, the terms and definitions given in EN 16575 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

organic material

material containing carbon-based compound in which the element carbon is attached to other carbon atoms, hydrogen, oxygen, or other elements in a chain, ring, or three-dimensional structure

3.2

isotope abundance

fraction of atoms of a particular isotope of an element

3.3

percentage modern carbon

pMC

normalized and standardized value for the amount of the ¹⁴C isotope in a sample, calculated relative to the standardized and normalized ¹⁴C isotope amount of oxalic acid standard reference material NIST SRM 4990c

Note 1 to entry: In 2020, the value of 100 % bio-based carbon was set at (100,0 ± 0,5) pMC.

Note 2 to entry: SRM 4990c, is the trade name of product supplied by the US National Institute of Standards and Technology. This information is given for the convenience of users of this document and does not constitute an endorsement by CEN of this product. Equivalent products may be used if they can be shown to lead to the same results.

3.4

laboratory sample

sub-quantity of a sample suitable for laboratory tests

3.5

sample

quantity of material, representative of a larger quantity for which the property is to be determined

3.6

sample preparation

all the actions taken to obtain representative analysis samples or test portions from the original sample

3.7

beta particle

electron emitted during radioactive decay

For the purposes of this document, the following symbols and abbreviations apply:

The ¹⁴C is present in products is originating from recent atmospheric CO₂. Due to its radioactive decay, it is almost absent from fossil products older than 40 000 years. The ¹⁴C content can thus be considered as a tracer of products recently synthesized from atmospheric CO₂ and particularly of recently produced bio-based products.

The determination of the bio-based carbon content is based on the measurement of ¹⁴C in bio-based products, which allows the calculation of the bio-based carbon fraction.

Extensive experience in ¹⁴C determination and reference samples is available from dating of archaeological objects, on which the three methods described in this document are based:

— Method A: Liquid scintillation-counter (LSC);

— Method B: Accelerator mass spectrometry (AMS);

— Method C: Saturated-absorption cavity ring-down (SCAR) spectroscopy.

NOTE The corresponding sampling methods are described in Annex A.

The advantages and disadvantages of these test methods are given in Table 1. In particular, the typical representative values of the absolute standard deviation (ASD) and the relative standard deviation (RSD), for 1h-long measurement of a modern sample (F = 100 pMC), are given, together with their dependence on the ¹⁴C-level in the sample (F). For all methods, both ASD and RSD scale with 1/√t, where t is the duration of the measurement. Based on the above general scaling laws, the typical range of measurement duration for practical use is also reported, together with the typical required carbon mass.

Table 1 — Advantages and disadvantages of the methods

For method A (LSC) a low-level counter shall be used. The statistical scattering of the radioactive decay sets a limit for method A. Indeed, since this method relies on counting, its precision is ruled by Poisson statistics and depends on the ¹⁴C level. The statistical uncertainty scales as sqrt(N), where N is the number of counted beta-decayed ¹⁴C atoms. Since the ¹⁴C level in the sample (F) is proportional to N, the absolute statistical uncertainty (ASD) will scale also with √F, and consequently the RSD will scale with 1/√F. Moreover, this method needs a purified carbon dioxide, otherwise nitrogen oxides from the combustion in the calorific bomb will result in counting losses by quenching and adulteration of the cocktail in case of LSC measurement. When using method A, samples with low bio-based carbon content (<10 %) can only be measured with sufficient precision using the benzene conversion procedure or, if applicable, direct LSC measurement, as described in B.4.3.

Since method B relies on counting ¹⁴C ions, its uncertainty is ruled by Poisson statistics, similarly to method A.

For method C (SCAR), differently from methods A and B, the absolute precision (ASD) is independent of the ¹⁴C level, as it depends only on the fixed instrumental sensitivity of the SCAR spectroscopic technique. Moreover, the carbon dioxide shall be sufficiently pure to avoid systematic errors in the ¹⁴C measurement. In particular, an overall purity from non-interfering gases of > 99,9 % is required. A few molecules (e.g. N₂O and SO₂) can directly interfere with the measurement, and their mole fraction shall be kept below the level of a few part-per-billion. Commercial elemental analysers are available ensuring a combusted CO₂ gas with these purity levels.

Especially for methods A and C, the duration needed for measurement spans over quite wide ranges, since it is related to the required measurement precision. Actually, in the best case of statistical uncertainty ruled by white noise, the precision always scales as 1/√ (t), where t is the averaging time.

NOTE Table 1 allows to quickly retrieve a rough estimate of the expected ASD and RSD for a measurement of a given duration (t) on a sample with a given ¹⁴C level (F). Four practical examples (see Tables 2 to 5) are reported below, showing longer and shorter measurement times and samples with higher and lower pMC.

Table 2 — Example 1: 30 min-long measurement of a 5 pMC sample

Table 3 — Example 2: 2 h-long measurement of a 5 pMC sample

Table 4 — Example 3: 30 min-long measurement of a 75 pMC sample

Table 5 — Example 4: 2 h-long measurement of a 75 pMC sample

A general sample preparation and three test methods for the determination of the ¹⁴C content are described in this document. With this modular approach, it will be possible for laboratories with standard equipment to prepare samples for the ¹⁴C content and determine the ¹⁴C content with own equipment or to outsource the determination of the ¹⁴C content to laboratories that are specialized in this technique.

For the collection of the ¹⁴C content from the sample, generally accepted methods for the conversion of the carbon present in the sample to CO₂ are described in Annex B.

For the measurement of the ¹⁴C content, two methods (LSC and AMS) that are already generally accepted as methods for the determination of the age of objects are selected. A third method (SCAR) is also selected, which has been specifically developed for the purpose of bio-based carbon measurements.

The amount of bio-based carbon in the bio-based product is proportional to its ¹⁴C content.

Complete combustion (see Annex B) shall comply with the requirements of the subsequent measurement of the ¹⁴C content. It shall ensure the quantitative recovery of all carbon present in the sample as CO₂ in order to yield valid results.

This measurement shall be carried out according to one of the three following methods:

— Method A: Liquid scintillation counter (LSC): indirect determination of the isotope abundance of ¹⁴C, through its emission of beta particles (interaction with scintillation molecules), in accordance with Annex C;

— Method B: Accelerator mass spectrometry (AMS): direct determination of the isotope abundance of ¹⁴C, in accordance with Annex D; or

— Method C: Saturated-absorption cavity ring-down (SCAR) spectroscopy: indirect determination of the isotope abundance of ¹⁴C, through absorption of infrared photons from ¹⁴CO₂ molecules, in accordance with Annex E.

In Annex A sampling methods for products that are mentioned in the scope are given.

For any sampling procedure, the samples shall be representative of the material or product and the quantity or mass of the sample shall be accurately established.

The conversion of the carbon present in the sample to a suitable sample for the determination of the ¹⁴C content shall be carried out according to Annex B.

The measurement of the ¹⁴C content of the sample shall be performed according to one of the methods as described in Annexes C, D and E.

When CO₂ captured in an absorption solution is sent to specialized laboratories, this shall be stored in a way that no CO₂ from air can enter the absorption solution. A check on the leak of CO₂ from air shall be performed by preparing laboratory blanks during the sampling stage.

For the determination of the 0 % bio-based carbon fraction the combustion of a fossil reference material (such as coal or ancient Kauri wood) shall be used.

NOTE There are several certified reference materials available, e.g. IAEA-C1 and IAEA-C9.

For validation of the 100 % bio-based carbon fraction, oxalic acid standard reference material NIST SRM 4990c shall be used. Mixing reference material NIST 4990c with a known amount of fossil combustion aid improves its combustion behaviour, as oxalic acid is difficult to combust due to its low calorific value. For routine checks, a fresh wood sample calibrated against the standard reference material is sufficient.

The calculation of the bio-based carbon content includes the following steps:

a) the determination of the total carbon content of the sample, x^TC, expressed as a percentage of the total dry mass (for method A);

b) the calculation of the bio-based carbon content by mass, x_B, using the ¹⁴C content value, determined by calculation from one of the test methods specified in 7.3, and applying the correction factors detailed in 7.2 (for method A);

c) the calculation of the bio-based carbon content as a fraction of the total carbon content, (see 7.3.2) (for methods A, B and C).

Before the above-ground hydrogen bomb testing (started around 1955 and terminated in 1962), the atmospheric ¹⁴C level had been constant to within a few percent for the past millennium. Hence, a sample grown during this time has a well-defined “modern” activity, and the fossil contribution could be determined in a straightforward way. However, ¹⁴C created during the weapons testing increased the atmospheric ¹⁴C level to up to 200 pMC in 1962, with a decline to 100 pMC in 2020. The ¹⁴C activity of a sample grown since year 1962 is elevated according to the average ¹⁴C level over the growing interval. In addition, the large emission of fossil C during the last decades contributes to the decrease of the atmospheric ¹⁴C/¹²C ratio.

The 100 % bio-based C reference value shall be taken from ASTM D6866, which is updated yearly. Other values may be used if evidence can be given on the pMC value of the bio-based part of the material.

Calculation of ¹⁴C content by method A (LSC)

Calculate the bio-based carbon content by dry mass, x_B, expressed as a percentage, using Formula (1):

(1)

where

¹⁴C_activity is the ¹⁴C activity, expressed in dpm, of the sample obtained by calculation when using method A (see Annex C);

REF is the reference value, expressed in pMC, of 100 % bio-based carbon of the biomass from which the sample is constituted;

m is the mass, expressed in grams, of the sample.

NOTE The pMC value of NIST SRM 4990c is set at 134,07, being 100 pMC equivalent to a ¹⁴C activity of 13,56 dpm/g C.

Calculation of ¹⁴C content by method B (AMS) or method C (SCAR)

Calculate the bio-based carbon content by dry mass, x_B, expressed as a percentage, using Formula (2):

(2)

where

x^TC is the total carbon content, expressed as a percentage, of the total dry mass of the sample;

pMC(s) is the measured value, expressed in pMC, of the sample;

REF is the reference value, expressed in pMC, of 100 % bio-based carbon of the biomass from which the sample is constituted.

Calculate the bio-based carbon content as a fraction of the total carbon content,, expressed as a percentage, using Formula (3):

(3)

where

x_B is the bio-based carbon content by dry mass, expressed as a percentage;

x^TC is the total carbon content, expressed as a percentage, of the sample.

Formula (3), though valid for all methods, can be simplified in case of methods B and C as shown in Formula (4) below:

(4)

The independent measurement of x^TC is not necessary for these methods.

EXAMPLE 1 Measurement according to method A

Sample made from pure wood (REF = 112 pMC, x^TC = 48,0 %)

Dry mass of sample: m = 1,010 g

¹⁴C activity = 7,34 dpm

EXAMPLE 2 Measurement according to method B and method C

Sample made from bark (REF = 112 pMC, x^TC = 52,0 %)

pMC(s) (measured ¹⁴C value) = 61,7 pMC

EXAMPLE 3 Calculation of bio-based carbon content as a fraction of TC

Pure bio-based polymer material

Sample made from PLA material: (x^TC = 50,0 %; x_B = 50 %)

Table 6 gives examples of calculations of for different materials.

Table 6 — Examples

See Annex F.

The test report shall contain at least the following information:

a) a dated reference to this document (EN 16640:202x);

b) all information necessary for complete identification of the bio-based material or product tested;

c) identification of the laboratory performing the test;

d) sample preparation;

e) storage conditions;

f) test method used for the determination of the ¹⁴C content (method A, B or C , see Annex C, D or E);

g) results of the test including the basis on which they are expressed and application of the isotope correction, including a precision statement;

h) method for the conversion of the carbon (see Annex B);

i) ¹⁴C activity, expressed in dpm, of the sample (for method A) or ¹⁴C value, expressed in pMC (for methods B and C);

j) either:

1) total carbon content, x^TC, expressed as a percentage, of the sample and bio-based carbon content by dry mass, x_B, expressed as a percentage, of the sample (for method A); or

2) bio-based carbon content by total carbon content, , expressed as a percentage, of the sample (for methods B and C);

k) any additional information, including details of any deviations from the test methods and any operations not specified in this document which could have had an influence on the results;

l) date of receipt of laboratory sample and dates of the test (beginning and end).

1. 
   (informative)
   
   Procedures for sampling of products

If available, product-sampling procedures for the determination of the total carbon content shall be used. If no such standard is available, a list of suitable standards is given in Table A.1 as guidance.

In the case of solid products, the sampling procedures mentioned in Table A.1 shall be used. If the procedure for solid product sampling is not available, then EN ISO 21645 or EN ISO 21646 shall be used.

Table A.1 — Sampling procedures

1. 
   (normative)
   
   Procedure for the conversion of the carbon present in the sample to a suitable sample for ¹⁴C determination
   1. General

In this annex, all steps are described to prepare samples for ¹⁴C determinations. In this way, a laboratory that is not equipped for ¹⁴C analysis can prepare their samples for distribution to laboratories that are equipped for ¹⁴C analysis.

For the determination of the ¹⁴C content, the carbon that is present in the sample has to be converted to CO₂.

The conversion is done by combustion in oxygen. If necessary, a combustion aid can be used to ensure complete oxidation of the carbon to CO₂.

For a number of liquid samples, no conversion to CO₂ is needed and direct measurement of the ¹⁴C content can be performed using LSC.

• 1. Sample preparation

For sample preparation procedures the following standards found in Table B.1 can be used:

Table B.1 — Sample preparations

• 1. Preparation for ¹⁴C measurement
     1. General

The ¹⁴C content of a bio-based product is determined on the CO₂ produced by the sample combustion. For the conversion of the sample to CO₂, used for the determination of the ¹⁴C content, the following three methods are allowed:

— combustion in a calorimetric bomb;

— combustion in a tube furnace;

— combustion in a laboratory scale combustion apparatus.

For gaseous samples, combustion in a calorimetric bomb is not applicable.

Conversion of gaseous hydrocarbons to CO₂ can be done at temperatures from 600 °C, using a suitable catalyst and absorption of the CO₂ in a NaOH solution as described in B.3.2.

In case of combustion, it depends on the method to be used for the determination of ¹⁴C content, how the formed CO₂ is collected and prepared for the measurement.

In method A (Annex C), three options are possible after combustion:

a) direct absorption of the formed CO₂ in a carbamate solution;

b) absorption of the CO₂ in a 2 M NaOH solution and transfer of CO₂ in NaOH to a carbamate solution;

c) direct conversion of CO₂ to benzene.

Method A (Annex C) can handle sample sizes down to 1 g, depending on the x^TC values.

When method B (Annex D) is used, there are three CO₂ collection options:

a) direct collection of the formed CO₂ in a gas-bag;

b) absorption of CO₂ in a 4 M NaOH solution;

c) absorption in a for this purpose developed solid absorber, usually NaOH or KOH fixed on a silica carrier or zeolite or adsorbents which can trap and release carbon dioxide to such an extent that this enables measurement without changing the ¹⁴C/¹³C/¹²C isotope ratios.

Method B (Annex D) can handle sample sizes down to a few µg, depending on the x^TC values.

In case of method C (Annex E), there are three CO₂ collection options:

a) direct collection of CO₂ in a glass ampoule;

b) selective adsorption by a zeolite trap;

c) absorption of CO₂ in a 4 M NaOH solution or KOH solution (pH > 13 during the whole adsorption).

Method C can handle sample sizes down to a few mg, depending on the x^TC values.

• • 1. Reagents and materials

— carbamate solution;

— scintillation medium;

— glass bottles (standard glass sample bottles with plastic screw caps that are resistant to 4 M NaOH);

— 4 M NaOH absorption liquid;

— glass ampoules (standard glass sample ampoules with vacuum-tight polytetrafluoroethylene (PTFE) valve for gas collection);

— liquid nitrogen (for the cryogenic separation of the CO₂ gas sample from the He carrier gas);

— zeolite pellets.

For the preparation of a carbonate free absorption liquid, preparation using freshly opened NaOH pellet containers is sufficient. Dissolve the NaOH pellets in a small amount of water (the heat produced during the dissolution process will enhance the dissolution process). Small amounts of precipitation are an indication of the presence of Na₂CO₃. By decanting the clear phase the almost carbonate free solution is diluted to the desired volume. As the dissolution of NaOH is an exothermic process extra care shall be taken as boiling of the concentrated solution during dilution can occur.

• 1. Combustion of the sample
     1. Combustion of the sample in a calorimetric bomb

For the combustion of the sample in a calorimetric bomb, any suitable test method, such as EN ISO 1716, ISO 1928 or EN ISO 21654, shall be used.

After the complete combustion in the oxygen bomb the combustion gases are collected in a gas bag.

For products that are difficult to combust, use a combustion aid to obtain complete combustion. Examples of combustion aids are polyethylene combustion bags, benzoic acid and glucose. Take care not to exceed the maximum amount of organic material allowable for the oxygen bomb that is used. Determine the amount of ¹⁴C present in the combustion aid and correct for the contribution of the use of the combustion aid (¹⁴C content and total carbon content).

Determination of the carbonate content in the solution that is collected after combustion can be used to determine the yield of conversion. The carbonate content shall be equivalent to the amount of total carbon present in the combusted sample (including combustion aid).

When method A is used, the CO₂ shall be collected in a 4 M NaOH solution prior to the conversion to benzene or collected in a cooled mixture of carbamate solution and a suitable scintillation liquid.

For the collection of CO₂ in 4 M NaOH solution, use a 250 ml washing bottle filled with 200 ml 4 M NaOH solution, apply a flow of 50 ml/min.

For the collection of CO₂ in a carbamate solution the gas sample bag is connected to a pump with a connection line into a 20 ml glass vial, filled with a mixture of 10 ml of the carbamate sorption liquid and 10 ml of the scintillation cocktail, placed in an ice bath, to remove the heat of the exothermic carbamate formation reaction. The pumping speed is low, typically 50 ml × min⁻¹ to 60 ml × min⁻¹. The transfer of the gas from the bag takes about 2 h to 3 h. After the sample has been collected, it is ready to be counted on a liquid scintillation counter. Blank samples shall also be counted at the same time to allow that small day-to-day variations in the background can be accounted for.

Measurements shall be done as soon as possible after collection, at the latest within one week after sampling. There are strong indications that the NO_x formed during the combustion reacts with the absorption mixture resulting in yet unexplained errors after a few days of storage. If the one week limit cannot be realized, collection of the CO₂ in a 4 M NaOH solution is a good alternative.

When method B is used, the carbon dioxide shall be collected in a 4 M NaOH solution or on a suitable solid absorber.

For method B, alternatively ca 2 ml of the CO₂ gas can be taken from the bag using a glass syringe and the gas can be transferred to the AMS target preparations system. As the bomb volume is released to atmospheric pressure, there will be a residual amount left over in the bomb that is directly related to the pressure in the bomb after the combustion.

NOTE With a residual pressure of 2,5 MPa, 4 % of the combustion gas will be left after release to atmospheric pressure.

To overcome this artefact:

a) perform the calibration and the analysis taking account of this residual amount by using the pressure correction factor;

b) use the vacuum pump to remove the residue;

c) flush the bomb with argon and collect the CO₂ in the rinsing gases as well.

• • 1. Combustion of the sample in a tube furnace or a combustion apparatus

The tube furnace or the combustion apparatus (e.g. a commercial-grade elemental analyser) shall be able to combust the bio-based product, with a complete conversion of the carbon present to CO₂. For the determination of the ¹⁴C content by method A the CO₂ shall be collected using a suitable impinger filled with a cooled mixture of carbamate and a suitable scintillation liquid, a scintillation medium already containing a CO₂ absorber or a 4 M NaOH solution (see B.3.2, second paragraph). For the determination of the ¹⁴C content by method B the CO₂ shall be collected using a suitable impinger filled with a 4 M NaOH solution. As a result of the absorption of the CO₂ a large volume reduction of the gas volume will be observed after trapping. Therefore, the gas pump is to be positioned in front of the impinger and the gas pump used shall be gas tight.

As an alternative, the CO₂ can be trapped by means of a cryogenic or zeolite trap. In that case the cryogenic trap shall consist of a water trap (dry ice in ethanol or acetone) followed by a cryogenic trap. Care shall be taken to avoid formation of liquid oxygen, which can be achieved by heating the trap slightly above the boiling point of oxygen, using liquid argon or performing the separation at diminished pressure. As an alternative, when method C is being used, dry CO₂ eluted from an elemental analyser shall be purified from the He carrier gas by a liquid-nitrogen trap or by a zeolite trap with selective CO₂ adsorption/desorption properties.

• • 1. Direct LSC measurement on the product

For liquid clear products, direct measurement on the bio-based product with the LSC technique is possible. This option is only allowed if equivalence to the methods with conversion to CO₂ can be demonstrated. This will in general be the case if no quenching is observed, or if correction for quenching is performed using standard addition technique with the same, ¹⁴C labelled, bio-based product containing known ¹⁴C activity.

The dissolution method might not be appropriate to some bio-based products, for instance when fillers are present.

For direct LSC measurements, DIN 51637 is recommended.

• 1. Normalization of LSC measurement results

A liquid scintillation counter measures β-decay counts of ¹⁴C (in counts per minute, cpm) indirectly by measuring the interaction signals of the β particles with scintillation molecules (emission of photons -light- proportional to the decay energy). For this measurement, sample CO₂ is either absorbed in a suitable absorbing solution to which also a scintillation reagent is added (CO₂-cocktail) or the CO₂ has been converted to benzene and is then mixed with liquid (scintillation) reagents to a benzene-cocktail. The benzene-cocktail method is more precise than the CO₂-cocktail method.

The same normalization as used for AMS and proportional gas counters shall be used for LSC measurement results:

(B.1)

In the case that no primary or secondary reference standard has been measured, the measuring efficiency is not cancelled out and shall be determined using an internal standard. It is also necessary in that case to determine the activity of the sample in dpm/g C instead of cpm/g C.

 = (13,56 ± 0,07) dpm/g C = (0,226 ± 0,001) Bq/g C.

• 1. Normalization of AMS and SCAR measurement results

The AMS system measures the carbon isotopes ¹²C, ¹³C and ¹⁴C of a carbon sample in the same sample run. A batch of samples shall also contain reference material samples. The measured ¹⁴C amount (=¹⁴C isotope concentration) in a sample is calculated relative to the measured (average) ¹⁴C amount of the reference material samples in the same batch. If the reference material is the primary reference standard Oxalic Acid II (HOx-II, SRM 4990c), which is commonly used for this purpose, the standardized ¹⁴C amount in the sample, (= = pMC), shall be calculated as following:

(B.2)

Similarly, all percentage modern carbon (pMC) values obtained from the SCAR measurements shall be corrected for isotopic fractionation using stable isotope data (¹³C/¹²C ratios) obtained on CO₂ derived from combustion of the sample, e.g. through an in-line isotope ratio mass spectrometer.

1. 
   (normative)
   
   Method A - Liquid scintillation-counter method (LSC)
   1. General

This annex describes the method for the determination of the ¹⁴C content by LSC in carbonate solutions or carbamate solutions obtained from the combustion of bio-based product samples in a calorimetric bomb, a tube furnace or a laboratory scale combustion device as described in Annex B.

• 1. Principle

The liquid scintillation counter (LSC) method determines the isotope abundance of ¹⁴C indirectly, through its emission of beta particles due to the radioactive decay of the ¹⁴C isotope. The beta particles are observed through their interaction with scintillation molecules. The CO₂ formed by the combustion of a bio-based product is trapped in an alkaline or carbamate solution. The CO₂ present in the alkaline solution is converted to benzene; the carbamate solution can be directly measured. The formed benzene or carbamate solution is mixed with the organic solution containing the scintillation molecules and the ¹⁴C activity of this mixture is measured in a liquid scintillation counter.

• 1. Reagents and materials

— oxalic acid primary standard (e.g. SRM 4990c);

— HCl solution (5 M);

— scintillation liquid;

— carbamate solution;

— ¹⁴C substance for standard addition purposes;

— coal standard;

— reagent grade powdered lithium or lithium rod (each packed in argon);

— reagent grade potassium chromate (in sulfuric or phosphoric acid);

— suitable catalyst (based on Cr₂O₃ or V₂O₅).

• 1. Apparatus

The low natural levels of radiocarbon in the earth's atmosphere (about 10⁻¹² %) require extra precautions for accurate measurement of ¹⁴C. Care shall be taken to eliminate the influence of cosmic and environmental background radiation, other radioisotopes being present, electronic noise and instability, and other factors. These background factors limit the accuracy, precision, and range of the radiocarbon method as finite ages can only be calculated where sample activity is at least three standard deviations above background activity (see ASTM D3665). Any liquid scintillation counter used shall meet these specifications.

• 1. Procedure
     1. General

The best LSC performance characteristics are obtained applying conversion of the collected CO₂ to benzene and direct counting of the benzene in a suitable scintillation cocktail, as for instance described in ASTM D6866. For material with a high bio-based carbon content (>10 %) direct absorption of the CO₂ in a carbamate solution can be applied.

• • 1. Benzene conversion

The collected CO₂ is reacted with a stoichiometric excess (3:1 lithium: carbon ratio) of molten lithium which has been preheated to 700 °C. Li₂C₂ is produced by slowly bleeding the CO₂ onto the molten lithium in a stainless steel vessel (or equivalent) while under a vacuum of < 135 mPa. The Li₂C₂ is heated to at least 640 °C and placed under vacuum for 15 min to 30 min to remove any unreacted gases and to complete the Li₂C₂ synthesis reaction. The Li₂C₂ is cooled to room temperature and gently hydrolysed with distilled or de-ionized water to generate acetylene gas (C₂H₂) by applying the water in a drop-wise fashion to the cartridge. Passing it through dry ice traps dries the evolved acetylene, and the dried acetylene is subsequently collected in liquid nitrogen traps. The acetylene is purified by passing it through a phosphoric acid or potassium chromate (in sulphuric acid) trap to remove trace impurities, and by using dry ice traps to remove water. The C₂H₂ gas is catalysed to benzene (C₆H₆) by bleeding the acetylene onto a chromium catalyst which has been preheated to ≥ 90 °C applying a water jacket cooler to avoid decomposition from excessive heat generated during the exothermic reaction. As an alternative, a vanadium catalyst at ambient temperature can be used. The benzene is thermally evolved from the catalyst at 70 °C to 110 °C and then collected under vacuum at −78 °C. The benzene is then frozen until it is counted. Radon can be removed by pumping on the benzene while it is at dry ice temperature. Mix the benzene and scintillation liquid in constant volume and proportion, if necessary, the benzene can be diluted with benzene from fossil origin (99,999 % pure, thiophene-free).

If ¹³C isotope analysis is required, a representative extra subsample shall be taken for ¹³C analysis.

• • 1. Direct absorption of the CO₂ in a carbamate solution

An absorption flask is loaded with a known volume of CO₂ absorbent, e.g. with Carbosorb® X^[2]. The absorbing capacity of Carbosorb® X of about 4,8 × 10⁻³ M/ml shall be taken into account; no more than 80 % of this capacity shall be used. The flask shall be cooled in ice during the absorption process. After absorption of the CO₂, the absorbent is transferred to the measuring vial. An equal volume of the scintillation medium is added, and the mixture is homogenized.

The CO₂ may also be absorbed in a scintillation medium already containing a CO₂ absorber, which shall be measured in the LSC without further handling.

Then the vial containing the mixture is placed in the LSC and measured. Typical counting times are 2 h to 24 h.

• • 1. Measurement

The activity of a sample is compared with the activity of a reference material. The number of ¹⁴C registrations (beta counts of ¹⁴C decay) in radiometric detectors (LSC) is related to the number of registrations of the reference sample under the same conditions.

Standard addition techniques shall be used to check for the occurrence of chemical or optical quenching for each sampling or sample type. For that purpose, ¹⁴C labelled components shall be used.

For clear liquids direct LSC counting can be applied, e.g. as described in DIN 51637; mix 10 ml of the sample with 10 ml of a suitable scintillation cocktail and count after 12 h settling time. For each product a quench curve shall be established before measurements can be done.

As ¹³C isotope analysis is required, an extra representative subsample shall be taken for ¹³C analysis.

• • 1. Blank correction

Measurement shall be performed together with a measurement of the blank sample, which is a scintillation vial filled with counting liquid that is counted for at least the same period of time as the actual sample. The result obtained is the background level for the whole system (apparatus and reagent) given in cpm or dpm. After this the actual sample is counted, which also gives a counting result in cpm or dpm.

The statistical error of counting, background and standard is a result of the decay counting (Poisson process); hence the precision of the result depends on the number of counts observed, where the relative error is inversely proportional to the square-root of the number of counts. The total error is then the combination of the analytical errors and the errors of the standard and background determination.

• 1. Calculation of the results

From the sample count rate, the background count rate of the counter is subtracted (net count rate). The ¹⁴C activity (dpm/g C) is obtained by normalizing the net count rate to the count rate of the reference standard (oxalic acid SRM).

Normalization of the LSC results shall be done as described in B.5.

1. 
   (normative)
   
   Method B - Accelerator mass spectrometry (AMS)
   1. General

This annex describes the procedure for the determination of the ¹⁴C determination by AMS in the carbonate solutions obtained from the combustion of bio-based product samples in a calorimetric bomb, a tube furnace or a laboratory scale combustion device as described in Annex B.

• 1. Reagents and materials

— oxalic acid primary standard (e.g. SRM 4990c);

— coal standard;

— iron or cobalt catalyst;

— hydrogen;

— HCl solution (5 M);

— dry ice;

— acetone or ethanol;

— liquid N₂.

• 1. Apparatus

— sample preparation equipment;

— liquid nitrogen freezing station;

— accelerator mass spectrometer (AMS).

• 1. Procedure

In practice every AMS lab performs their measurements using their own optimized measurement procedures. An example of a procedure is given in this clause. Comparable procedures can be used as long as the AMS results are obtained using the same reference standard (SRM 4990c).

a) Transfer the carbonate solution to the extraction bottle.

b) Attach the HCl dosing device.

c) Evacuate the bottle and dosing device (degassing, removal of dissolved N₂ and O₂ from air).

d) Add HCl to the carbonate solution.

e) Remove water vapour by using a trap filled with acetone and dry ice.

f) Collect the formed CO₂ in a trap that is submersed in liquid N₂.

g) Take a small sample for ¹³C determination at this stage.

h) Transfer the CO₂ to the graphitizing rig system.

Gaseous samples shall be either introduced in the system released from a quartz tube or after they are trapped in liquid nitrogen followed by subsequent heating. Then convert the gas to graphite using an iron catalyst according to the formulae:

CO₂ + H₂ ↔ H₂O + CO

CO + H₂ ↔ H₂O + C

i) Remove the water produced by this reaction to ensure a complete reduction to graphite. This is particularly important to avoid fractionation.

j) Press the graphite into a target and mount it on a wheel before it is loaded into the accelerator mass spectrometer. In the ion source a high current beam of caesium ions (Cs⁺) is focused on the target. This liberates negatively charged target atoms, producing a 36 keV beam of C^- ions. Keep the targets 10 mm away from each other to avoid cross-contamination and move them during sputtering to avoid cratering, which causes fractionation. A lens into a recombinator then focuses the negative ion beam. Here a series of magnets remove non-carbon ions from the beam and separate the three carbon isotopes (¹²C, ¹³C and ¹⁴C). The chopper wheel then physically blocks most of the ¹²C, allowing a much-reduced beam of carbon ions to be recombined for simultaneous injection into the accelerator.

k) In the tandem accelerator the C^- ions are accelerated to the terminal (at +2,5 MeV) then changed to C³⁺ ions by collision with Ar atoms in the gas stripper. These positive ions are accelerated to 10 MeV. A charge state of 3+ is chosen because the mass/charge ratio of ¹⁴C³⁺ is truly unique, allowing its accurate separation in the high-energy mass spectrometer.

l) Measure the ¹²C and ¹³C in the Faraday cups (typical current, 250 nA).

m) Purify the ¹⁴C³⁺ ions by an electrostatic deflector and a 90° magnet. Measure them in an isobutene-filled ionization chamber, isolated from the accelerator vacuum by a thin metal foil. Typically, a sample is counted for one hour.

• 1. Calculation of the results

The isotopic ratios of ¹⁴C/¹²C and ¹³C/¹²C are determined relative to the appropriate primary reference material. All percentage modern carbon (pMC) values obtained from the radiocarbon analyses measurements shall be corrected for isotopic fractionation using stable isotope data (¹³C/¹²C ratios) obtained on CO₂ derived from combustion of the sample. Determination of ¹³C/¹²C ratios on the sample itself can lead to erroneous results in some cases. Normalization of the AMS results shall be done as described in B.6.

1. 
   (normative)
   
   Method C - Saturated-absorption cavity ring-down (SCAR)
   1. General

This annex describes the procedure for the determination of the ¹⁴C content by SCAR spectroscopy in the CO₂ gas obtained from the combustion of bio-based product samples in a laboratory scale combustion device as described in Annex B. For practical use, the sample combustion procedure for SCAR analysis has been tested and validated using commercially available elemental analyzers. An important specification to be taken into account is the capability of the elemental analyser in reducing the nitrogen and sulphur oxides (see below).

• 1. Principle

The SCAR spectroscopy quantifies the mole fraction of the ¹⁴C¹⁶O₂ isotopologue within a CO₂ gas sample. This technique is based on the highly selective absorption of infrared photons from these ¹⁴C-containing molecules only. Since the mole fraction of a modern sample is about 1 part per trillion (ppt), the absorption sensitivity must be enhanced down to a few parts per quadrillion (ppq) by using a very long interaction path between the radiation and the molecules. A quantum cascade laser provides photons at 4,5 µm wavelength for the interrogation of the target absorbing molecular transition. A 1 m long optical cavity made by two high-reflectivity mirrors provides an effective interaction path even longer than 20 km, depending on the quality of the mirrors. The cavity is filled with the sample gas at a given pressure and temperature, precisely measured (0,1 % relative uncertainty). After the laser beam is switched off, photons stored inside the cavity start escaping out of it and this exponential decay is detected by a photodiode. The decay rate depends on both cavity losses and absorption from the sample gas, which, due to the saturated-absorption regime, can be independently retrieved during each single ring-down event. This measurement is repeated thousands of times for each spectral point. For each forward/backward frequency scan, tens of spectral points are measured step by step over the absorption transition. A complete spectrum is acquired in a few minutes. The spectrum can contain also an interfering line from N₂O, when the mole fraction of this molecular species is not suppressed below 10 ppb. Another interfering species, SO₂, can alter the baseline shape and should be suppressed below 1 ppt, to avoid possible systematic effects. The recorded spectral area of the target ¹⁴C¹⁶O₂ transition is proportional to the ¹⁴C content and the pMC value is calculated by comparing it with that recorded for the oxalic acid standard. With SCAR, the modern fraction in the carbon present in the sample, is determined. The total carbon content is not determined with this technique and shall be determined separately.

NOTE In general, when using an elemental analyser, the CO₂ purity is sufficient. The appearance of a distortion of the signal is an indication that the analyser is not working properly.

• 1. Reagents and materials

— oxalic acid primary standard (e.g. NIST SRM 4990c);

— blank standard material (e.g. fossil coal, IAEA-C-1 standard);

— liquid N₂;

— high-purity 99,999 % He (gas carrier for the combustion device);

— high-purity 99,999 % O₂ (comburent for the combustion device).

• 1. Apparatus

— sample preparation equipment for weighing and properly cleaning before combustion;

— elemental analyser for sample combustion;

— CO₂ collection and purification bench;

— ¹⁴C-SCAR analyser.

• 1. Procedure

The main measurement procedure is carried out as described in the following steps:

a) Install and evacuate a glass ampoule (volume > 50 ml) where the sample will be collected.

b) Weigh a proper sample mass in a tin cup with a precision balance to the nearest 0,1 mg and record the result (at least 6 mg of carbon are needed).

c) Enclose the solid/liquid sample in the tin cup and seal it removing as much ambient air as possible. The contamination by ambient air is not critical for the final result.

d) Freeze the ampoule with a liquid N₂ bath. Less than 1 l of liquid N₂ is required for this task.

e) Burn the sample in the elemental analyser.

f) Collect the output CO₂ gas and the He carrier gas in the pre-evacuated and frozen glass ampoule, and wait until the elemental analyser has released all of the CO₂.

g) Pump the He out of the frozen ampoule, so that only frozen CO₂ remains under vacuum.

h) Heat the ampoule back to room temperature.

i) Transfer the CO₂ gas to the ¹⁴C-SCAR cell.

j) Record the ¹⁴CO₂ absorption spectrum, choosing the averaging time according to the required precision.

k) Fit the spectrum to a 2-Voigt profile, also including the possible nearby interfering N₂O transition.

l) Calculate the pMC value of the sample by normalizing the sample spectral area to the area of the oxalic acid standard (134,06 pMC). (see E.6)

In case of use of a zeolite trap instead of a glass ampoule and a liquid-nitrogen bath, the following steps shall replace the steps with the corresponding letters in the above main procedure while keeping the other steps the same as above:

a) Evacuate the zeolite trap while heating it to ~400 °C in order to purge it. Then cool it back to room temperature and keep it under vacuum until the sample is ready for loading.

b) Ensure that the zeolite trap is at room temperature and under vacuum.

c) Let the output CO₂ gas and the He carrier gas flow through the zeolite trap and wait until the elemental analyser has eluted the whole CO₂.

d) Pump the He out of the zeolite trap.

e) Heat the zeolite trap to ~400 °C in order to release the CO₂ sample.

f) Transfer the CO₂ gas to the ¹⁴C-SCAR cell. This step requires a direct connection between the zeolite trap and the ¹⁴C-SCAR instrument.

In case of use of a 4 M NaOH or KOH solution, steps a) to f) above shall be replaced with the following, while keeping steps g) to l) the same as in the main procedure above:

a) Transfer the NaOH or KOH solution to the extraction bottle.

b) Remove gases from the system with a flow of helium.

c) Add phosphoric acid (5M) to the alkali solution.

d) Remove water vapour and interfering gases from the gas flow by using magnesium perchlorate and copper heated to 550 °C.

e) Collect the formed CO₂ in an ampoule that is submersed in liquid N_2.

Calibration of the system shall be performed daily.

• 1. Calculation of the results

The isotopic ratios of ¹⁴C/¹²C are determined relative to the appropriate primary reference material. All percentage modern carbon (pMC) values obtained from the radiocarbon analyses measurements shall be corrected for isotopic fractionation using stable isotope data (¹³C/¹²C ratios) obtained on CO₂ derived from combustion of the sample, through an isotope ratio mass spectrometer. Determination of ¹³C/¹²C ratios on the sample itself can lead to erroneous results in some cases. Normalization of the SCAR measurement results shall be done as described in B.6

1. 
   (informative)
   
   Performance characteristics

The round robin assessment was initiated in the frameworks of the European KBBPPS and Open-Bio projects (https://www.biobasedeconomy.eu/). The aim of the study [52] was to investigate the performance characteristics of the method that was described in CEN/TS 16640:2014 for the bio-based carbon content determination.

The assessment involved 11 independent laboratories to whom in total 132 samples were delivered (11 equivalent sets of samples, 12 samples in each set). The round robin was carried out by laboratories in Germany, France, Poland, the Netherlands, New Zealand, the United Kingdom and the USA. According to the aim of the study, each participating laboratory was asked to follow the method proposed in CEN/TS 16640:2014 and to determine the total carbon content and subsequently the bio-based carbon content of different types of materials or products. The selection of samples for the assessment was done to cover different and challenging materials. The set of samples that were sent to each laboratory involved: water soluble matt paint with volatile component about 34 %; non-volatile emulsions used as components of sun lotion and in cosmetics; a panel made from wheat straw that can be used for building purposes; bio-diesel; biogas; surfactant granules that are used in cosmetics; multilayer packaging film; silk paint; binder that is used in paints; wooden particle board ground to 0,5 mm. All results were reported on dry basis.

For the description of the sample types, see Table F.1.

The performance data according to ISO 5725‑2 are presented in Table F.2.

Table F.1 — Description of sample types

Table F.2 — Performance data for ¹⁴C methods

A study has been carried out to investigate the performance characteristics of method C (added in this version of the standard) for the bio-based carbon content determination.

The study involved 8 independent institutions interested in assessing the accuracy of method C by performing a blind comparison with method B. Each institution provided a group of samples of its own interest, for a total of 58 different matrices. Each matrix was provided in two equivalent samples: one was analysed by an AMS laboratory, the other was analysed by a SCAR facility. Different AMS laboratories in France, Hungary, and the USA, as well as different SCAR laboratories in Italy were involved.

Each participating laboratory was asked to determine the percentage modern carbon in pMC units.

The selected samples cover different materials and a wide range of ¹⁴C content (0 pMC to 115 pMC). The samples matrices were of the following types: diesel, gasoline, jet-fuel, algae-derived oil, polymer film, polymer pellets, plastic tools for food use, natural and artificial leather materials.

For the description of the involved institutions see Table F.3.

A concise summary of the results of the blind intercomparison between methods B and C is presented in Table F.4, where the root-mean square deviation between the results given by SCAR and AMS is reported for each intercomparison campaign. For more details, a synthesis report on the intercomparison between methods B and C can be consulted in Annex G.

The procedure followed in this intercomparison activity (many samples sent to two laboratories at a time) is not the same as the one followed for the round robin assessment originally performed for method B (few samples sent to many laboratories at a time, see the beginning of this annex). However, the total numbers of unique measurements performed (116) and of laboratories involved (9) is comparable with the number of measurements performed (116) and of laboratories involved (11) in the round robin assessment, ensuring a comparable statistical representativeness of the results.

Table F.3 — Description of involved insitutions

Table F.4 — Blind intercomparison between methods B and C

1. 
   (informative)
   
   Synthesis report on AMS - SCAR intercomparison measurements
   1. Summary

This annex presents the results of an intercomparison study that was performed to investigate the performance characteristics of the SCAR method.

In total, the assessment involved 8 institutions that in the period 2019 to 2024 carried out 9 independent intercomparison campaigns, with a total of 116 samples tested (58 sets of samples with 2 samples in each set).

The intercomparison studies were carried out to determine the average agreement of the SCAR method against the AMS method.

The results of the performed assessments showed a good consistency. The average discrepancy (with sign) is very close to 0 (−0,27 pMC), suggesting that no systematic bias is present between the two methods. The obtained root-mean-square (RMS) discrepancy of 1,01 pMC is comparable with the average reproducibility standard deviation of the round robin assessment presented in Annex F, involving both method A (LSC) and method B (AMS).

Based on the performed validation of method C presented in this report, the absolute discrepancy is observed to be independent of the product’s nature, of the performed sample preparation and of the amount of bio-based carbon in the sample.

• 1. Description

The SCAR technique was first demonstrated in 2011, as a general technique allowing trace-gas detection with ultra-high sensitivity [53]. Afterwards, its application to ¹⁴C detection in sub-natural concentration levels has been investigated and demonstrated [54, 55]. Since then, the SCAR method has been tested and implemented by several institutions for intercomparison measurements against AMS, which was used as a reference method, in order to validate the method for their specific application.

Each intercomparison campaign was conducted independently from the others and handled autonomously by the institution. The typical process was the following:

— The institution selected a set of samples of interest.

— Each sample was split into two or more sub-samples.

— One sub-sample was measured by an AMS facility for ¹⁴C analysis.

— The other sub-sample was measured by SCAR ¹⁴C analysis.

— The sample pre-treatment and preparation were performed at the measurement sites (AMS and SCAR), so the comparison also includes the possible discrepancies added by the preparation processes.

— All the AMS and SCAR measurements have been performed without knowing the results of the other technique (blind measurements).

— The results were independently collected by the institution, who compared them and shared the results.

In total, the assessment involved 9 different institutions, and 116 samples were tested (2 equivalent sets, 58 samples in each set, one measured by an AMS laboratory, the other by a SCAR laboratory). Table G.1 gives an overview of the institutions and the laboratories participating in the intercomparison campaigns.

Table G.1 — General description of the involved institutions and employed facilities

• 1. Results

The results of the AMS-SCAR intercomparison measurements over the 58 sets of samples are reported in Table G.2. Table F.3 and Table F.4 are based on these results.

Each sample is identified by its name, when available the type of sample is also specified. For each sample the SCAR and AMS results are given in pMC units, and the absolute and relative deviations are calculated. The RMS deviation is calculated over the campaign results (last column in Table G.2). From the columns of the absolute and relative deviations, after having removed the outliers, the following indices are retrieved:

— The total root-means-square deviation (RMS dev, 1-sigma): it represents the average level of agreement between the two methods.

— The maximum deviation (MAX dev): it gives the maximum discrepancy occurred between the two methods over the whole set of measurements.

— The signed average deviation (AVG dev): if not close to zero, it indicates the presence of a systematic bias between the two methods.

The outliers have been identified by first calculating the RMS and average deviations over the whole set of data and then looking for the values falling outside the 3-sigma interval from the average.

Table G.2 — Intercomparison results between method B (AMS) and method C (SCAR)

Based on the analysis described above, 1 outlier has been found (marked in grey in Table G.2), coming from the first intercomparison campaign A (2019). The maximum value for the discrepancy (2,48 pMC) was observed for the third campaign C (2022).

For campaigns C and G the results are also published and discussed in scientific papers, and the corresponding reference is given.

• 1. Conclusions

The results of performed assessment show a good consistency between method B (AMS) and method C (SCAR). A low number of outliers (1 outlier) was observed, and the average discrepancy (with sign) is very close to 0 (−0,27 pMC), suggesting that no systematic bias is present between the two methods. The agreement between the two methods of the more recent campaigns is settling on a level lower than 1 pMC, while the total RMS deviation over the full set of results is 1,01 pMC.

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[2] EN ISO 1716, Reaction to fire tests for products - Determination of the gross heat of combustion (calorific value) (ISO 1716:2018)

[3] EN ISO 21645, Solid recovered fuels - Methods for sampling (ISO 21645:2021)

[4] EN ISO 21646, Solid recovered fuels - Sample preparation (ISO 21646:2022)

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[30] ASTM C172/C172M, Standard Practice for Sampling Freshly Mixed Concrete

[31] ASTM C224, Standard Practice for Sampling Glass Containers

[32] ASTM C322, Standard practice for sampling ceramic white-ware clays

[33] ASTM C1704/C1704M, Standard test method for sampling and testing structural cementitious panels

[34] ASTM D233, Standard test methods for sampling and testing turpentine

[35] ASTM D268, Standard guide for sampling and testing volatile solvents and chemical intermediates for use in paints and related coating and material

[36] ASTM D802, Standard test methods for sampling and testing pine oils

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[38] ASTM D1485, Standard practice for rubber from natural sources — Sampling and sample preparation

[39] ASTM D2915, Practice for sampling and data analysis for structural wood and wood-based products

[40] ASTM D3437, Standard Practice for Sampling and Handling Liquid Cyclic Products

[41] ASTM D3665, Standard practice for random sampling of construction materials

[42] ASTM D4057, Standard practice for manual sampling of petroleum and petroleum products

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[51] EPA 340/1-91-010, Standard procedure for collection of coating and ink samples for analysis by reference methods 24 and 24A

[52] https://www.biobasedeconomy.eu/app/uploads/sites/2/2017/07/Open-BIO_D3_1_RR1_final-2.pdf

[53] Giusfredi G., Bartalini S., Borri S., Cancio P., Galli I., Mazzotti D. et al. Phys. Rev. Lett. 2010, 104 p. 110801

[54] Galli I., Bartalini S., Borri S., Cancio P., Mazzotti D., De Natale P. et al. Phys. Rev. Lett. 2011, 107 p. 270802

[55] Galli I., Bartalini S., Ballerini R., Barucci M., Cancio P., De Pas M. et al. Optica. 2016, 3 p. 385

[56] Carcione F., Defeo G.A., Galli I., Bartalini S., Mazzotti D. Coatings. 2023, 13 p. 892

[57] Varga T., Molnár M., Varricchio L., Carcione F., Detti A., Bartalini S. J. Clean. Prod. 2024, 483 p. 144319

1. A mandate is a standardization task embedded in European trade laws. Mandate M/492 was addressed to the European Standardization bodies, CEN, CENELEC and ETSI, for the development of horizontal European Standards for bio-based products. ↑

2. Carbosorb® X is a trademark of Phebra. This information is given for the convenience of users of this document and does not constitute an endorsement by CEN of the product named. ↑