Analytical Methods

A detailed description of the EBC analytical methods developed and accredited for biochar. Please refer to the EBC guidelines version 10.4 from 20th December 2024.

The current issue date of the respective standard is applicable. Descriptions in this annex may contain deviations and/or concretizations regarding the listed methods. If no ISO method is applicable to the biochar matrix, the required analytical method is described below the parameter. For further reference, corresponding non-ISO methods are listed.

Sample preparation (ISO 13909-4, DIN 51701-3):

After homogenization, the sample is divided representatively into portions. This subsampling is done by quartering (quarter method) of the homogenized sample. At least 1000 g of the original sample is needed for all analyses and, if necessary, several replicates.

A portion of the sample is dried at 40 ° C and is divided into some subsamples after drying and homogenization. Approximately 250 g of the 40 ° C dried and uncrushed sample is used to determine the salt content, pH, bulk density as delivered, and BET surface area of the material. Approximately 50 g of the 40 ° C dried sample is finely ground in a vibratory mill. After homogenization, the fine material is subsampled for further analysis (i.e., PAH, ash, CHNOS, trace, and major elements, conductivity). Unless otherwise specified, the particle size of the analytical samples is specified by the respective methods and standards.

Bulk density for ground particle sizes < 3 mm (ISO 17828, analog VDLUFA-Method A 13.2.1):

To calculate bulk density, a dried, water-free sample of at least 300 ml is poured into a graduated cylinder, and the mass is determined by weighting. The volume of the sample is read after 10 times compression by means of falling. The bulk density (on dry matter base) in kg / m³ is calculated from the mass and the volume of the sample.

Bulk density of the unground sample as delivered (DIN EN ISO 17828):

Only for particle sizes between 0.3 mm and 30 mm. The sample is analyzed as delivered, not dried, not milled.

NOTE: The bulk density of freshly produced biochar is subject to fluctuations due to several factors, such as vibrations, shocks, pressure, drying, and humidification. The measured bulk density may, therefore, have been altered by transport, storage, or handling.

Salt content (electrical conductivity of leachate) - in analogy to DIN ISO 11265:

Add 20 g of the sample to 200 ml of desalinated water and shake it for 1 hour, followed by filtration of the solution. The conductivity is then measured using the filtrated water. The temperature correction is automatically done on the measuring device. The electrical conductivity is given for a solution at 25°C. The salt content is calculated using the factor 52.8 [mg KCl/l]/[10^-4/cm] and is given in mg KCl/l. This is based on the conductivity (14.12 * 10^-4 S/cm) of a 0.01 molar KCl solution.

pH-value DIN ISO 10390 (CaCl₂):

A minimum of 5 ml of the air-dried sample is placed in a glass vessel. Five times the volume (25 ml) of a 0.01 M CaCl₂ solution is added. The suspension is overhead rotated for 1 h. The suspension obtained is directly measured with a pH meter.

Water content according to ISO 589, DIN 51718, specified as follows:

Method A / two-step method (Reference method for coal)

Raw moisture

The sample (100 to 1000 g) is spread evenly in a drying bowl crucible, weighed with 0,1 g accuracy and dried in an oven at (40 ± 2) ° C until the mass is constant. If necessary, the sample is divided and dried in more than one crucible.

Analysis: raw moisture (FG) in%

FG = raw moisture in %

m_E = mass of the sample before drying in g

m_R = mass of the sample after drying in g

Hygroscopic moisture

Hygroscopic moisture is the moisture held firmly within the pore structure of biochar. Measuring hygroscopic moisture will lead to an understanding of a particular biochar's ability to hold and release moisture.

A subsample of the air-dried and crushed (grain size < 1 mm) sample is weighed immediately after the subsampling into a TGA crucible and is dried in a nitrogen atmosphere at (106 ± 2) ° C to constant mass.

Evaluation: hygroscopic moisture (FH) in %

FH = hygroscopic moisture in %

m_E = mass of the sample before drying in g

m_R = mass of the sample after drying in g

Water content

Evaluation: water content (Wt) in %

W_t = water content in %

FG = raw moisture in %

FH = hygroscopic moisture in %

Ash content (550 °C) ISO 1171, DIN 51719:

To determine the ash content in biochar two programs of the TGA (30 or 60 min) could be used. The weight determination of the crucible is carried out automatically. Enter the sample number for corresponding crucible position. Add 1.0 g of the sample to the ceramic crucible and spread the substance evenly in the crucible. Weighing is done automatically relative to the crucible position.

Runs the following heating program in the oven:

heating with a rate of 5 K / min to 106 ° C under a nitrogen atmosphere to constant mass (Δm <0,05%).

temperature increase with 5 K / min to 550 ° C under oxygen atmosphere,
hold this temperature for 30 or 60 min to constant mass (m <0,05%).

The ash content is automatically determined and calculated for the sample used.

Carbonate CO₂ according to ISO 925, DIN 51726:

1 g of pre-dried and ground sample is weighed to 0.2 mg and placed in the decomposition flask. The device consists of an absorption tower, which purges the air of carbon dioxide, the decomposition flask with an attachment to add the decomposition acid, and three connected washing bottles. The carbon dioxide freed air is sucked through the system. After the system is purged and the washing bottles are filled with an absorbing solution of BaCl₂ and NaOH solution, 30 ml decomposition acid (hydrochloric acid with HgCl₂ as a catalyst and a wetting agent) are added to the decomposition flask. The content of the decomposition flask is boiled for about 10 minutes. The inert gas flow transports the carbon dioxide produced through the acidic solution in the first wash bottle in the other two wash bottles. In the second wash bottle, the carbon dioxide dissolves under the consumption of base and is precipitated as barium carbonate. If something precipitates in the third wash bottle, the measurement must be repeated with a lower initial mass. The consumption of base in the second wash bottle is determined by pH-titration using hydrochloric acid. The carbonate content of the sample is calculated from the base consumption and is calculated as CO₂.

CHN according to ISO 29541, DIN 51732:

The use of TruSpec Micro or comparable devices is recommended. The sample is combusted in a stream of pure oxygen. Resulting CO₂, H₂O and nitrogen oxides are quantified to calculate the elemental composition.

Sulphur according to ISO 19579, DIN 51724-3:

The pre-dried and crushed sample is weighed in a ceramic crucible. At high temperatures (> 1300 ° C), the sulfur is oxidized in an oxygen stream with the aid of a V2O5 catalyst layer. The resulting SO₂ is detected in an Infrared cell and calculated with the sample mass as total sulfur content.

Oxygen (calculation) according to ISO 17247, DIN 51733:

The oxygen content is a parameter derived from calculations. It is assumed that the biochar sample consists essentially of ash, carbon, hydrogen, nitrogen, sulfur, and oxygen. If one subtracts the ash, carbon, hydrogen, nitrogen, and sulfur content in percent from 100 %, the result will be the oxygen content in percent.

C_org, molar H/C and molar O/C (calculation):

Other quantities and ratios can be calculated from the determined data.

C_org is derived from the total carbon content minus the inorganic carbon content (CO₂) in the sample. The H content is analyzed through CHN-analysis (see above). To calculate molar ratios, the determined mass fractions of the elements must be converted into molar quantities. To do this, the value must be divided by the respective molar mass (carbon: 12.001 g mol^-1, hydrogen: 1.008 g mol^-1, oxygen: 15.999 g mol-1).

PAH according to DIN EN 17503 (extraction method 10.2.3 using toluol)

Currently, no ISO method exists for the analysis of PAHs in biochar. Therefore, the following method based on DIN EN 17503 must be used. A 2.5 g sample of pre-dried and crushed biochar is extracted with at least 100 ml of toluene using Soxhlet extraction for six hours. The extract is then concentrated to a volume of 10 ml, and an internal standard is added. An aliquot of the extract is measured using GC-MS or an equivalent measurement method.

Trace metals after microwave-assisted digestion according to EN ISO 12846, DIN 22022-1, DIN 22022-7, DIN EN ISO 17294-2 / DIN EN 1483:

(Pb, Cd, Cu, Ni, Hg, Zn, Cr, B, Mn, As, Ag)

Microwave digestion currently, no ISO method exists for microwave digestion of biochar)

The pre-dried and crushed sample is weighed and placed into the reaction vessel of the microwave. 10 ml of nitric acid and 2 ml of hydrofluoric acid are added. The reaction vessel is sealed and placed in the microwave.

Program flow of the microwave pressure digestion:

heating (room temperature to 240° C) for 15 min

holding time at 240 ° C for 20 minutes

free cooling

additional only for ICP-OES:

Program flow of the fluoride masking (Boric acid, adding 5 ml of saturated solution):

heating (room temperature to 160 ° C) in 8 minutes

holding time at 160 ° C for 7 minutes

free cooling

After complete cooling, the reaction vessels are opened, and the digestion solution is transferred to a 50 mL plastic volumetric flask and filled with deionized water.

The diluted solution is measured by ICP-MS (DIN EN ISO 17294-2).

To determine the levels of mercury DIN EN ISO 12846, DIN 22022-4, DIN EN ISO 17294-2, and DIN 22022-7 can be used.

Main elements after melting digestion according to ISO 23380, DIN 51729-11, DIN EN ISO 11885 / DIN EN ISO 17294-2: (P, Mg, Ca, K, Na, Fe, Si, S):

The melting process is performed on the biochar ashes. 200 mg of the fine ash is weighed into a platinum crucible and thoroughly mixed with 2 g of lithium metaborate.

The platinum crucible is placed in a digestion oven. The digestion remains at least 15 minutes at 1050 ° C in the oven. The melt is dissolved in hydrochloric acid and filled to 500 ml.

The samples are measured with ICP-OES (DIN EN ISO 11885) or ICP-MS (DIN EN ISO 17294-2).

Declaration of the nutrient content

The content of nitrogen, phosphorous, magnesium, calcium and potassium must be stated in g kg^-1 of nitrogen, P₂O₅, MgO, CaO and K₂O, respectively, referring to dry matter of biochar. It is recommended to provide all main elements (for P, Mg, Ca, K additionally) as g kg^-1 (element, not oxide) and the results of elemental analysis and calculation (CHNSO, C_org, carbonate) in % of dry matter of biochar.

Water holding capacity (WHC) according to DIN EN ISO 14238, annex A

Water-holding capacity. This can be measured using the method DIN EN ISO14238, annex A. The test consists of soaking the 2mm fraction of the material in a water-filled test tube for a period of 24 hours. After this, the test tube should be covered with filter paper and placed upside-down on a dry sand bed for 2 hours to remove free water. The saturated material should then be weighed and then dried at 40°C in a compartment dryer. After drying, the material should be weighed again to estimate the water-holding capacity.

Electrical conductivity of the pyrogenic solid

To determine the conductivity of the solid biochar, it is first necessary to compress the finely ground biochar under standardized pressure. The defined compression is usually done in the EBC-endorsed Black Gauß I device (c.f., https://zenodo.org/records/8197758), where the electrical resistance is then measured vertically through the test specimen. Based on the measured resistance of the biochar and the geometry of the compacted matter, the specific conductivity can be determined.

For the determination of the conductivity, a device for compressing the biochar, a multimeter with the capability of 4-wire measurement and a measuring construction in which the biochar can be compressed and the electrical resistance can be measured at the same time are required. The measuring construction consists of a pressure flask whose bottom and lid each consist of corresponding copper electrodes. The electrodes used are to be connected to an external multimeter.

In an exemplary setup, for example, a sample chamber volume of 10 cm³ results in a relevant weighing range of 1-2 g of a sample dried at 40 °C and finely ground for analysis. A pressure in the range of 10 - 50 kN must be applied to this test setup using a hydraulic press (e.g., toggle press). When the specified target pressure is reached, the resistance is immediately read on the multimeter and converted using the above formulas. The average conductivity is obtained from the mean value of the solid conductivities under 10, 20, 30, 40 and 50 kN pressure.

This method was developed by the Ithaka Institute and Eurofins. The necessary measuring equipment can be obtained from Eurofins. The establishment of an ISO standard for this measurement method is currently being attempted.

Analytical Parameters for EBC-FeedPlus and EBC-Feed (not required for WBC)

The current issue date of the respective standard applies. Further descriptions in this annex may contain deviations and/or concretizations with regard to the mentioned standard. The explanations in italics are only intended to provide the reader with basic information; the implementation is based exclusively and precisely on the standard referred to.

Trace metals As, Pb, Cd, Hg

DIN EN 15763

For microwave digestion, 0.1 g to 1 g of the dried, ground, and homogenized material is weighed into a plastic cup (PTFE, PFA) or quartz cup. After addition of 65% nitric acid in a ratio of 1+5 (sample+acid) and after addition of 30% hydrogen peroxide in a ratio of 1+2.5 to 1+10 (sample+hydrogen peroxide), digestion is performed at the maximum permissible temperature for the system (usually 190°C). Heating phase: 15 min; holding time: 30 min.

After cooling, transfer quantitatively to a polypropylene vessel with a volume marker and fill it to the mark with 0.1 M nitric acid. The measurement is carried out by ICP-MS or ICP-OES. For mercury, cold vapor AAS or atomic fluorescence spectrometry is used.

PCB

DIN EN 16167, DIN EN 16215

The material is crushed into powder (<1 mm) and dried at a maximum of 35 ° C. Alternatively, it can be dried chemically or by freeze-drying. 5-10 g of sample are extracted by Soxhlet extraction with toluene for 6 h with the addition of suitable internal standards. Alternatively, an ASE extraction can be used. The extract is concentrated and purified according to VDLUFA VII 3.3.2.2 with silica gel column chromatography. The quantification of the purified extract is done with GC-MS or GC-ECD.

PCDD/PCDF/coplanar PCB

DIN EN 16190, DIN EN 16215, Commission Regulation (EC) No 152/2009 (modified by No 2017/771) - HRGC/HRMS method

The material is crushed into powder (<1 mm) and dried at a maximum of 35 ° C. Alternatively, freeze-drying can be used. After the addition of isotope-labeled standards, 2 g of sample material are extracted with toluene in a Soxhlet for 20 h. Alternatively, special hot extractors such as the ASE can be used. After concentration, the extract is purified by multiple column chromatography and can be divided into different fractions. At this point it is also possible to obtain the DIN-PCB fraction. Finally, the components are measured with GC-HRMS.

Fluor
ISO 11724, VDLUFA III 17.3.2, VDLUFA VII 2.2.2.1, DIN EN 16279 (ion selective electrode; according to VDLUFA VII 2.2.2.1), BAFU F-7 2017 (DIN 38405-4):

The dried and ground material is ashed and digested with sodium hydroxide. The cooled digestion is dissolved in hydrochloric acid with the addition of a complexing agent (TISAB). A pH value of 5.5 is then adjusted, and the fluoride content is determined using an ion-sensitive electrode.

Dry matter
Permitted test methods: dry matter: ISO 589, DIN 51718, VDLUFA III 3.1:

A minimum of 50 g of the sample is taken and crushed as necessary, avoiding changes in moisture content. 5 g of biochar are weighed (±1 mg) and dried at 103°C for 4 h. After loading the oven, the drying time does not start until 103°C has been reached exactly. After cooling in the desiccator, it is weighed back (±1 mg).

Crude ash

Permitted test methods: analog to ISO 1171, DIN 51719, VDLUFA III 8.1m HCl-insoluble ash: VDLUFA III 8.2m, specified as follows:
Approximately 5 g of sample is weighed to the nearest 1 mg into an annealed and tared ashing dish. The dish is placed in a muffle furnace and left at 550°C±5°C until no char particles are visible. After cooling in the desiccator, the sample is weighed back to 1 mg. For difficult samples, ammonium nitrate treatment is carried out according to method VDLUFA 8.1.

Additional Parameters

Gross calorific value / net calorific value according to ISO 1928, DIN 51900:

To determine the calorific value, a bomb calorimeter that fulfills the requirement of the stated standard is used. 0,3 to 0,8 g of pre-dried and ground sample is weighed into a combustion bag, capsule, or crucible. The sample is mounted in the combustion bomb with an ignition wire and 10-20 ml of eluent in the bottom part of the bomb. The bomb is placed into the calorimeter. The oxygen filling, the ignition, and the measurement are done automatically. After combustion, the bomb must be checked for signs of incomplete combustion. The gross calorific value is calculated using the calibration and measurement data. With further corrections, the net calorific value is calculated.

Ash content (815 °C) ISO 1171, DIN 51719:

The ash content at 815 ° C is determined after determining the ash content at 550 ° C by rising the temperature from 550 ° C with 5 K / min to 815 ° C and holding until constant weight (mass difference ± 0,05%) is reached.

Volatile matter according to ISO 562, DIN 51720:

1,0 g of the pre-dried and ground sample is placed into a crucible (with lid). The sample must form a uniformly thick layer on the bottom of the crucible. The crucible is placed in the oven preheated at 900 ± 5 ° C. After 7 minutes (± 5 sec), the crucible is removed from the oven and reweighed after cooling to room temperature. The volatile matter content is calculated from the mass loss of the sample.

PCB

VDLUFA VII 3.3.2.2 (DIN-PCB; hot extraction, GC-MS) DIN EN 16167 (use extraction method 2 with Toluol and not with light petroleum), DIN 38414-20 and DIN EN 16215. No ISO method for biochar PCB exists, use the procedures as follows:

The sample is crushed into powder (<1 mm) and dried at a maximum of 35 ° C. Alternatively, it can be dried chemically or by freeze-drying. 5-10 g of sample are extracted by Soxhlet extraction with toluene for 6 h with the addition of suitable internal standards. Alternatively, an ASE extraction can be used. The extract is concentrated and purified according to VDLUFA VII 3.3.2.2 with silica gel column chromatography. The quantification of the purified extract is done with GC-MS or GC-ECD.

PCDD/PCDF/coplanar PCB according to DIN EN 16190:2019-10, DIN EN 16215, Commission Regulation (EC) No 152/2009 (modified by No 2017/771) HRGC/HRMS method, No ISO method for biochar PCDD/PCDF/coplanar PCB exists, use the procedures as follows:

The sample is crushed into powder (<1 mm) and dried at a maximum of 35 ° C. Alternatively, freeze-drying can be used. After the addition of isotope-labeled standards, 2 g of sample material is extracted with toluene in a Soxhlet for 20 h. Alternatively, special hot extractors such as an ASE can be used. After concentration, the extract is purified by multiple-column chromatography and can be divided into different fractions. At this point, it is also possible to obtain the DIN-PCB fraction. Finally, the components are measured with GC-HRMS.

Specific surface area according to DIN ISO 9277 (BET):

The samples should be dried at 40°C and milled to a particle size < 3.15 mm. Nitrogen is used as the adsorption gas. Degassing temperature and time are set to 150°C and 2 hours. The degassing has to be done under a vacuum. The multipoint BET method should be applied.

Chrom(VI)

DIN EN 16318. No ISO method for biochar Chrom(VI) exists, use the procedures as follows:

Chromium cannot be oxidized during pyrolysis and is instead reduced during pyrolysis, i.e., Cr(VI) is converted into less mobile and dramatically less toxic Cr(III), which is already regulated as the total Cr content of biochar. Nevertheless, this method is offered to provide analytical evidence of compliance with the requirements of the EU Fertilizer Product Regulation, if required.

Particle size distribution ISO 1953

Particle size distribution is determined by sieving according to DIN 66165 or ASTM D2862, based on local preferences and equipment availability. For this purpose, suitable sieves with ascending mesh sizes are stacked on top of each other. The sample is placed on the uppermost, widest-meshed sieve, and then the apparatus is operated for a defined time so that the biochar is sieved dry by shaking or shaking and tapping. After that, the oversize on each sieve is weighed.

Biochar that has been pre-sieved to less than 2 mm or ground appropriately can also be analyzed for particle size distribution using laser diffraction according to ISO 13320. The specifications of the instrument must be adhered to so that the technically largest possible biochar particles can also still be measured.