Analytical Methods

A detailed description of the EBC analytical methods developed and accredited for biochar.

The EBC and it's accredited partner labs work continuously to improve the performance, reliability, and comparability of biochar analysis. All accredited labs participate in annual ring trials organized by DCC Delta Coal Control GmbH.

 

(version 10.1E from January 10th, 2022)

 

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 (i.e., PAH, TGA, ash, CHN, S, trace and major elements). Unless otherwise specified, the particle size of the analytical samples is specified by the respective methods and standards.

 

Bulk density (analogue 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.

 

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 then measured using 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):

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 DIN 51718:

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 %

            mE        =         mass of the sample before drying in g

            mR        =         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 %

            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 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 (m <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 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 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 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 is used to measure carbon, hydrogen and nitrogen (CHN)
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 placed in the machine for measurement. The TruSpec CHN determines CHN as a percentage of mass.

 

Sulphur according to DIN 51724-3:

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

 

Oxygen (calculation) according to 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, sulphur and oxygen. If one subtracts the ash, carbon, hydrogen, nitrogen and sulphur content in percent from 100 %, the result will be the oxygen content in percent.


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. The H content is analysed through CHN-analysis (see above).

 

PAH analogue to DIN EN 15527: 2008-9 (extraction with Toluol); DIN EN 16181: 2019-08 with extraction method 2

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

The pre-dried and crushed sample is weighed and placed 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 DIN EN ISO 12846, DIN 22022-4; DIN EN ISO 17294-2, and DIN 22022-7 can be 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).

 

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

Water-holding capacity. This can be measured using the method DIN EN ISO 14238, annex A.

The test consists of soaking the 2mm fraction of the material in water for a period of 24 hours. After this, the material should be placed on a dry sand bed for 2 hours for removing free water. The saturated material should then be weighed and then dried at 105°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. During this compression process, 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 using the formulas described in the EBC-guidelines version 10.1.

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. 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.

 



14. Analytical Parameter for EBC-Feed

Trace metals As, Pb, Cd, Hg
DIN EN 15763:2010-04

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 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 are used.

 

Benzo[a]pyren for EBC-Feed
DIN EN 16181:2019-08 (extraction method 2)

The material is crushed (<1 mm) and dried at a maximum of 35°C. 10 g of sample is extracted by Soxhlet extraction for 6 h with toluene with addition of appropriate internal standards. Alternatively, an ASE extraction can be used. The extract is concentrated and purified by column chromatography according to DIN ISO 13877 or VDLUFA VII 3.3.3.2. The purified extract can be measured and quantified by HPLC-FLD or GC-mass-spectrometry. MSD, MS/MS, HRMS or TOF instruments are suitable.

 

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 16190:2019-10, DIN EN 16215 Nr. 152/2009 (modified by Nr. 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
VDLUFA III 17.3.2, VDLUFA VII 2.2.2.1, DIN EN 16279:2012-09 (ion selective electrode; according to VDLUFA VII 2.2.2.1), BAFU F-7 2017 (DIN 38405-4:1985-07)

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.

 

Carbon
Permitted test methods: DIN 51732

A TruSpec CHN 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.

 

Dry matter
Permitted test methods: dry matter: 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 DIN 51719, VDLUFA III 8.1; HCl-insoluble ash: VDLUFA III 8.2
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.


 

15. Additional Parameters

 

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

To determine the calorific value a bomb calorimeter which fulfills the requirements 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 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) 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 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.

 

Specific surface area following DIN ISO 9277 (BET) and DIN 66137 (density)

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. 


 

Thermogravimetric analysis (TGA):

The TGA curve is determined, similar to how the ash content is measured, with the 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.

 

PCB
VDLUFA VII 3.3.2.2 (DIN-PCB; hot extraction, GC-MS) DIN EN 16167:2019-06 (use extraction method 2 with Toluol and not with light petroleum), DIN 38414-20 and DIN EN 16215

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
DIN EN 16190:2019-10, DIN EN 16215, (EG) Nr. 152/2009 (modified by Nr. 2017/771) HRGC/HRMS method

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 are 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.