Analytical Methods

The EBC and it's accredited partner labs work continously to improve the performance, reliability and comparitbility of biochar analysis. It participats in the EU-COST biochar ringtrial and participates also in other ringtrials.

Analysis of Biochar

version 4.1 (4th March 2014)


Basic Package

Sample preparation (DIN 51701-3):

After homogenization, the sample is divided representatively into portions.

This subsampling is done by quartering (quarter method) of the homogenized sample.

Approximately 100 g of the original sample are used for the determination of the conductivity, the salt content and pH.

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 true density and the BET surface 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 (PAK, TGA, ash, CHN, S, trace and major elements).


Bulk density (analogue VDLUFA-Method A 13.2.1):

The sample (at least 300 ml) is filled 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 density in kg / m³ is calculated from the mass and the volume of the sample.


Electrical conductivity (salt content) - Method of the BGK (Federal quality community compost), volume 1, method III. C2 – in analogy to DIN ISO 11265:

Adding 20 g of the sample to 200 ml desalinated water and shaking it for 1 hour, followed by filtration of the solution. The conductivity is measured then in the filtrated water. The correction of temperature is automatically done in 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):

Minimum 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 over head rotated for 1 h. The suspension obtained is directly measured with a pH meter.


Water content according to DIN 51718:

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

- raw moisture

The sample (1 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 %

                  mE            =               mass of the sample before drying in g

                  mR           =               mass of the sample after drying in g


- hygroscopic 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 %

                  mE            =               mass of the sample before drying in g

                  mR           =               mass of the sample after drying in g


-water content

Evaluation:  water content (Wt) in %


                  Wt            =               water content  in %

                  FG            =               raw moisture in %

                  FH            =               hygroscopic moisture in %


Ash content (550 °C) analogue DIN 51719:

To determine the ash content 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 in the ceramic crucible and spread the substance evenly in the crucible. The weighing is done automatically relative to the crucible position.

The oven runs the following heating program:

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

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

Conversion to other reference states is calculated externally.



The TGA curve is determined, like the ash content, with the LECO TGA. For this purpose, 1,0 g of pre-dried and ground sample is weighed in the TGA crucible. During the temperature rise from 30 ° C to 950 ° C with 10 K / min, the crucible is weighed at frequent intervals in the TGA furnace. The result is shown graphically.


Carbonate CO2 analogue 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 frees 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 purged and the washing bottles were 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 contents 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 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 a 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 DIN 51732:

A TruSpec CHN (Manufacturer: Leco) is used.
The sample (80-100 mg of the pre-dried and crushed sample) is weighed directly (relative precision 0,1%) into a tin capsule. After that the capsule is closed and is put in the machine for measurement. The TruSpec CHN determines the carbon content, the hydrogen content and the nitrogen content in mass percent.


Sulfur according to DIN 51724-3:

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


Oxygen (calculation) according to DIN 51733:

The oxygen content is a calculated parameter. It is assumed that the 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. During the ashing of biochar at 550°C, inorganic components of biochar may reduce or some CO2 may precipitate as carbonate both leading to increases of the total mass of the ash. The oxygen bound in those oxides may thus result in incorect and sometimes even negative oxygen values when calculated according to DIN 51733.


Corg, H/C und O/C (calculation):

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

Corg is derived from the total carbon content minus the inorganic carbon content (CO2) in the sample.


PAH analogue to DIN EN 15527 (extraktion with Toluol) GC-MS (DIN CEN/TS 16181):

2,5 g of the pre-dried and crushed sample is weighed into a extraction thimble and is extracted with 50 ml of toluene at reflux for two hours. The extract is concentrated to 10 ml. An aliquot of the extract is transferred to an injection vial and the PAH are analyzed by gas chromatography.


Gas chromatograph:    Network GC System 7890N and 5975C MSD and inertXL AS 7693 Fa: Agilent Techn

Capillary column:         HP 5MS (30 mx 0.25 mm x 0.25 microns)

Temperature program:  90 ° C (0.5 min), 20 ° C / min to 250 ° C, 5 ° C / min to 275 ° C, 20 ° C / min to 320 ° C for 5 min

Transfer line:                280 ° C

MSD temperature:        150 ° C

Injection volume:          1 µl

Injector temperature:    250 ° C

Carrier gas:                  Helium (1,5 ml / min)


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

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

The pre-dried and crushed sample is weighed into the reaction vessel of the microwave. 6 ml of nitric acid, 2,0 ml of hydrogen peroxide and 0,4 ml of hydrofluoric acid are added. The reaction vessel is sealed and is placed in the microwave.

Program flow of the microwave pressure digestion:

heating (room temperature to 190 ° C) in 15 min

holding time at 190 ° 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 in 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 a cold vapor AAS (DIN EN 1483) is used.


Main elements after melting digestion DIN 51729, DIN EN ISO 11885 / DIN EN ISO 17294-2:

(P, Mg, Ca, K, Na, Fe, Si, S)

The melting process is performed on the ashes of the biochar. 200 mg of the fine ash are 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).


Additional parameters


Gross calorific value / net calorific value according to DIN 51900:

For the determination of the calorific values a bomb calorimeter (IKA calorimeter C 5000 duo IKA C 5000) 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 bottom part of the bomb. The bomb is placed into the calorimeter. The oxygen filling, the ignition and the measurement are done automatically. After the 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) DIN 51719:

The ash content (815 ° C) is determined after the ash content (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 DIN 51720:

1,0 g of the pre-dried and ground sample is weighed 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.


Water holdung capacity (WHC) according to DIN ISO 14238-2011

Water-holding capacity. This can be measured using the method according to German Standard E DIN ISO 14238-2011; appendix A (draft).

The test consists of soaking the 2mm fraction of the material in water for a period of 24 hours. After this, the material has to be placed on a dry sand bed for 2 hours for removing free water. The saturated material has to be weight and then dried at 40°C in a compartment dryer. After drying the material has to be weight again for estimate the water holding capacity.