„A novel single-run dual temperature combustion (SRDTC) method for the determination of

organic, inorganic and total carbon“

• Isabella Bisutti,• Ines Hilke,• Jens Schumacher and• Michael Raessler

• Max-Planck-Institut für Biogeochemie, Hans-Knoell-Strasse 10, D-07745 Jena, Germany

Target:

• exact determination of inorganic and organic carbon in soil samples for evaluation of the carbon cycles on regional and global scales

• soils contain 2200 Pg (10 15 g) carbon in the first 100 cm

2/3 OC and 1/3 IC

• soils contain three times more carbon than above-ground biomass

„Classical“ methods for determination of OC and IC:

• combustion of sample to determine total carbon (TC)

• either acid or ashing pretreatment removes IC or OC

• remaining form of carbon is determined by combustion

• complementary part of carbon is calculated by difference

• ACID PRETREATMENT (ISO 10694)

• 1st combustion: TC 2nd combustion: OC

IC = TC - OC

Disadvantages (1)

• acid pretreatment:

• non-quantitative removal of carbonate carbon

• great variability of results

• possible loss of soluble OC

• possible loss of volatile organic carbon (VOC)

Disadvantages (2)

• ashing pretreatment:

• thermal instability of carbonates

• uncertainty of complete OC removal

• neither acid nor ashing pretreatment provide information on TC, OC and IC in ONE single analitycal run

Carbonate minerals in soil samples

Mineral TDecomp(̊C) Impact of temperature

Impact of acid

Calcite (CaCO3)

675$ 500°C / 7h no loss of carbonate; 600°C / 4h loss of about 90 %(13); 780°C / 15 min. completely converted (18)

5 – 25 s HCI 20 % (25); 1 h at 50°C H3PO4 (26)

Aragonite (CaCO3)

645

Dolomite (CaMg(CO3)2)

450§ 500°C / 16h loss up to 20% (1); 800 °C / 5 min. completely

Up to 24 h for total reaction (25, 26)

Magnesite (MgCO3)

425¥ 500°C / 4h loss up to 80 % (13)

Not dissolved with normal acid treatment (25); 52 days at 50°C H3PO4 (26)

Siderite (FeCO3)

425 550°C / 15 min. 93 % is decomposed (18)

See dolomite (25); 14 days at 50°C H3PO4 (26)

• Possible solution

• dry combustion at TWO DIFFERENT temperatures

• OC is combusted at lower T while higher T are needed for complete decomposition of IC

• Disadvantage

• samples have to be analyzed twice

• equilibration of furnace

• longer analyses times

• possible loss of VOC not detected

Suggested Solution: SRDTC

• instrumental device: „Liqui TOC“, Elementar GmbH

• dynamic heater with catalytic post-combustion

• TC,OC and IC from ONE sample with ONE analysis

• no loss of VOC; all carbon is oxidized

• indication of thermally instable carbonates

OVERVIEW OF SOIL SAMPLES

IC material Provider Origin Calcite Mineralogical Collection, Jena

(Germany) Iceland

Dolomite Mineralogical Collection, Jena (Germany)

Wolkenstein, Saxony (Germany)

Magnesite Mineralogical Collection, Jena (Germany)

Veitsch, Styria (Austria)

OC material Cellulose Fluka (Switzerland) Powder from spruce: length of

fibre: 0,02-0,15 mm Wood MPI for Biogeochemistry, Jena

(Germany) Spruce from Wetzstein, Thuringia (Germany), completely decomposed (Grade 5)

Reference HA (1R103H-2) IHSS (USA) Pahokee Peat, Florida (USA) Standard HA (1S104H) IHSS (USA) Leonardite, low grade coal, North

Dakota (USA) Coal lignite Argonne Premium Coal (USA) Beulah-Zap seam, North Dakota

(USA) Coal sub-bituminous Argonne Premium Coal (USA) Wyodak-Anderson seam,

Wyoming (USA) Coal high-volatile bituminous (1) Argonne Premium Coal (USA) Illinois #6 seam, Illinois (USA) Coal high-volatile bituminous (2) Argonne Premium Coal (USA) Pittsburgh seam, Pennsylvania

(USA) Coal medium-volatile bituminous

Argonne Premium Coal (USA) Upper Freeport seam, Pennsylvania (USA)

Oven temperature in °C

200 300 400 500 600 700 800 900 1000

% C

rec

over

ed

0

20

40

60

80

100

CalciteDolomite MagnesiteCelluloseWood Reference HA Standard HACoal lignite Coal subbituminous Coal high-volatile bituminous (1) Coal high-volatile bituminous (2)Coal medium-volatile bituminous

Selection of combustion temperatures

OC RECOVERY AT T = 500 °C

Compound Carbon Content in [%] Recovery in [%] Cellulose 40.8 103.2 Wood 55.5 99.4 Reference HA (peat) 49.6 98.4 Standard HA (leonardite)

58.6 99.9

Coal lignite 53.6 93.7 Coal sub-bituminous 57.8 95.8 Coal high-volatile bituminous (1)

59.5 94.3

Coal high-volatile bituminous (2)

64.7 87.3

Coal medium-volatile bituminous

71.2 91.4

Limitation: Elemental Carbon!

Synthetic mixtures and mixing ratios

• Mixture:

• Magnesite-Cellulose in sand• Magnesite-Wood in sand• Calcite-Cellulose in sand• Calcite-Wood in sand• Calcite-Cellulose in sand-bentonite• Calcite-Wood in sand-bentonite

• Ratio OC:IC in [%]

• 0.25 - 0.001• 0.25 - 1.00• 0.25 - 10.00• 2.5 - 1.00• 2.5 - 10.00• 5.00 - 0.1• 5.00 - 1.00• 5.00 - 10.00

Combustion of Lignine and Calcite

Recovery of SRDTC analyses of synthetic mixtures (N=216) OC 107 ± 23.1 %

IC 100 ± 16.9%TC 104 ± 6.7%

Mixture OC IC TC Magnesite – Cellulose in sand

2.8 3.1 2.1

Magnesite – Wood in sand

3.6 3.6 1.6

Calcite – Cellulose in sand

5.9 5.0 6.8

Calcite – Wood in sand

4.7 6.8 3.8

Calcite – Cellulose in sand - bentonite

2.9 2.5 1.9

Calcite – Wood in sand - bentonite

1.9 2.8 1.6

Expected OC vs.OC by SRDTC

% OC theoretic

0 1 2 3 4 5 6

% O

C b

y T

TC

0

1

2

3

4

5

6

7

Cellulose-MagnesiteCellulose-CalciteWood-MagnesiteWood-CalciteCellulose-Calcite in SBWood-Calcite in SB

SRDTC vs. ISO 10694

% OC by TTC

0 2 4 6

% O

C b

y D

IN

0

2

4

6

8

10

12

Cellulose-MagnesiteCellulose-CalciteWood-MagnesiteWood-CalciteCellulose-Calcite in SBWood-Calcite in SB

Acknowledgements

• Ralf Dunsbach, Klaus-Peter Sieper Elementar Analysensystem GmbH, Hanau, Germany

• Birgit Kreher-Hartmann, Mineralogische Sammlung, University of Jena

• Kristin Lober, Michael Rothe, Willi Brand, MPI Biogeochemie, Jena