Total (Organic) Carbon, Nitrogen and Sulfur Elemental Analysis of Soils and Eluates

Total (Organic) Carbon, Nitrogen and Sulfur Elemental
Analysis of Soils and Eluates
Webinar
Dr. Dominik Margraf

Agenda
Introduction1
CN(S) Analysis of Soils2
TOC Analysis of Soils and Soil Eluates3
6/11/2015 Soil and Eluates | Webinar

Elemental Analysis of Soil
“Studies predict the world population to increase beyond 8.2 billion within
the next 10 years, demanding ways to optimise the use of agrarian land
to provide a larger food supply.”
• Agricultural science and analytics are the key to
manage the fundamental growing demands for
food, feed and water.
www.gov.uk

Elemental Analysis of Soil
• Carbon and nitrogen are important drivers in the
element cycling of soils.
• Elemental analysis provides essential information
about microbiological activity and organic matter,
enabling a selective fertilization of arable land.
• Understanding the carbon-nitrogen ratio of soil is
therefore of utmost importance.

Agenda
Introduction1
CN(S) Analysis of Soils2
Sample Preparation2.1
Combustion Chemistry2.2
Gas Separation and Detection2.3
runAr Option: Argon vs. Helium as Carrier Gas2.4
TOC Analysis of Soils and Soil Eluates3

Challenges in Sample Preparation
• inhomogeneities within a sample
may cause large deviations
between two measurements
• solution
• milling
• grinding
• large representative sample
– multi gram scale

vario MAX cube CN(S)– Dedicated Soil Analyzer
• Sample is simply filled in upright,
reusable crucible
• Up to 5 g mineral sample
• Up to 5 ml liquid
• Up to 1 g organic sample

vario MAX cube CN(S) – Dedicated Soil Analyzer
• Automatic sample introduction via robotic arm
• soil samples form large amount of ashes
• time saving automatic ash removal
• high lab efficiency
• 90 position carousel as standard
• unattended 24/7 operation
• Robust, maintenance-free mechanical design

Combustion According to Dumas Method
Organic compounds consists of C, H, N, O, S, Cl …
Combustion in O2 on oxygen donor at ~ 900°C
O2, N2, NOx, CO2 CO, CH4, SO2, H2O, HCl...
Typical problem of macro analysis (50 – 5000 mg)
Combustion tube

Unique Post-Combustion
Organic compounds consists of C, H, N, O, S, Cl …
Combustion in O2 on oxygen donor at ~ 900°C
O2, N2, NOx, CO2 CO, CH4, SO2, H2O, HCl...
post-combustion on catalyst (and H2O removal)
O2, N2, NOX, CO2, SO2, HCl...
Post-combustion tube

Unique Reduction Using Tungsten
• Reduction tube for binding of excess oxygen
• Effective tungsten for CN mode: W  WO3
• one tungsten atom reacts with three oxygen atoms
• SO2 is bound on tungsten
• for CNS mode tungsten has to be replaced with copper
• Quantitative reduction of NOx to N2
• only N2, CO2 (and SO2 in CNS mode) exit reduction
tube
tungsten
Reduction tube

Advanced Purge and Trap Technology
• Prior to detection gases are separated
• unique Advanced Purge and Trap Technology
• absorption column specifically removes CO2 from gas stream and N2 is
being detected
• additional column in CNS mode to specifically absorb SO2
• CO2 absorption column is heated to desorption temperature
• all CO2 is released at one controlled point in time
– focused, sharp peaks without overlap
– separation of C/N ratios up to 7000 : 1

Thermal Conductivity Detector with 10 Year Warranty
• measuring principle
• difference in thermoconductivity
of gases causes detectable
temperature difference
carrier gas +
analyte gas
carrier gas
© http://wikipedia.de
gas thermoconductivity
[W/mK)]
H2 0,186
He 0,1567
Ar 0,0179
N2 0,0260
CO2 0,0168

Why Alternatives to Helium?
• helium is a limited resource
• Nobel Laureate Robert Richardson expects world
supplies to last another 40 years and suggests a
150-fold increase of the helium price
• USA will sell their helium reserves
Robert Richardson
Nobel Laureate in Physics 1996

Argon as Carrier Gas
• difference between argon and e.g.
CO2 large enough?
carrier gas +
analyte gas
carrier gas
© http://wikipedia.de
gas thermoconductivity
[W/mK)]
H2 0,186
He 0,1567
Ar 0,0179
N2 0,0260
CO2 0,0168

runAr Option Experimental Set-up
• instrument: vario MAX cube CN in
helium or argon mode
• samples: certified standard soils
• “sandy”, “loamy”, “silty”, “clay”,
“chalky”
• sample weight: approx. 1000 mg
• triple determination
• three independent measuring days
• identical operator

runAr Option Experimental Results Nitrogen
y = 1,014x + 1,554
R² = 0,99
0
50
100
150
200
250
300
350
400
0 100 200 300 400
ARGONCARRIERGAS;nitrogencontent
[ppm]
HELIUM CARRIER GAS; nitrogen content [ppm]
NITROGEN DAY 1
sandy
silty
loamy
clay
chalky
• excellent
experimental
correlation
• Day 2 and Day 3
summarized as table
• error bars indicate
3 x abs. SD (99%
confidence)
• for further information please
refer to
D. Margraf, Argon as Carrier Gas in CN
elemental analysis of soils, Bulletin of the
Swiss Chemical Soil Society, ISSN 1420-
6773

runAr Option Experimental Results Carbon
• excellent
experimental
correlation
• Day 2 and Day 3
summarized as table
• error bars indicate
3 x abs. SD (99%
confidence)
• for further information please
refer to
D. Margraf, Argon as Carrier Gas in CN
elemental analysis of soils, Bulletin of the
Swiss Chemical Soil Society, ISSN 1420-
6773
y = 1,000x + 63,716
R² = 0,999
0
1000
2000
3000
4000
5000
6000
0 1000 2000 3000 4000 5000 6000
ARGONCARRIERGAS;carboncontent[ppm]
HELIUM CARRIER GAS; carbon content [ppm}
CARBON DAY 1
sandy
clay; silty
loamy
chalky

runAr Option Summary Experimental Results CN
• mean experimental results of three
independent measuring days each
run in triple determination
• exp. results ± 3 x abs. SD at 99%
confidence interval
• Argon and helium based reveal
excellent agreement within the
experimental error
D. Margraf, Argon as Carrier Gas in CN elemental analysis of soils,
Bulletin of the Swiss Chemical Soil Society, ISSN 1420-6773
sample nitrogen
[ppm]
carbon
[ppm]
Helium Argon Helium Argon
Chalky 364 ± 8 370±9 5330±40 5370±50
Clay 188 ± 6 190±20 2080±40 2190±40
Loamy 255 ± 1 260±8 2640±20 2690±50
Sandy 60 ± 10 60±2 820±10 820±30
Silty 169 ± 2 180±10 2120±20 2180±60

runAr option Experimental Results CNS
• Sample amount: 250 – 850 mg
• exp. results ± abs. SD
• runAr also suitable for a variety of
matrices
C [%] N [%] S [%]
Soil
helium
argon
1.78 ± 0.01
1.78 ± 0.02
0.17 ± 0.001
0.18 ± 0.009
0.02 ± 0.001
0.01 ± 0.002
Maize
kernel
helium
argon
43.2 ± 0.02
43.2 ± 0.01
2.66 ± 0.01
2.75 ± 0.01
0.22 ± 0.01
0.24 ± 0.02
Wheat
flour
helium
argon
40.7 ± 0.04
40.5 ± 0.02
1.13 ± 0.002
1.17 ± 0.004
0.08 ± 0.005
0.08 ± 0.009

vario MAX cube – runAr Technology
• Use of Argon has been scientifically proven for
the analysis of soils
• No time-consuming retrofit needed
• Argon instead of helium as a carrier gas further
reduces cost-per-sample
• approx. 10% savings with runAr option
based on German gas prices
• runAr option is free of charge

vario MAX cube – Analysis of Soil
• Soil from banana plantation in Ecuador
• Sample weight: 1000 mg
• CN mode
Sample C
[%]
N
[%]
C/N
ratio
Fluvisol Ah horizon 1.488 ± 0.003 0.051 ± 0.001 29.2
Fluvisol B horizon 0.670 ± 0.001 0.065 ±0.001 10.3
Fluvisol B/C horizon 1.921 ± 0.004 0.024 ± 0.001 80.0

vario MAX cube – Analysis of Soil
• Soil from a pasture Southwest USA
• Sample weight: 550 - 750 mg
• six-fold determination
• 1 : 1 addition of WO3
Sample C
[%]
N
[%]
S
[%]
Cambisol Ah horizon 1.112 ± 0.001 0.104 ± 0.001 0.0229 ± 0.0005
Cambisol B horizon 1.782 ± 0.010 0.168 ±0.001 0.0231 ± 0.0004
Cambisol Cw horizon 0.335 ± 0.013 0.0532 ± 0.027 0.0094 ± 0.003
Calcisol B horizon 4.187 ± 0.015 0.051 ± 0.001 0.0873 ± 0.0028

vario MAX cube – TC and TOC Analysis
• full agreement with ISO 10694
• TC sample weight: 1000 mg
• TOC sample weight: 300 mg
• external acidification with 10% HCl
in silver foil cups
• dried at 80°C in silver foil cups
• silver foil cups simply placed in
crucible
• TIC accessible by difference
TC [%] TOC [%]
Soil 1 2.91 ± 0.08 1.33 ± 0.01
Soil 2 2.61 ± 0.06 2.34 ± 0.02
Soil 3 0.525 ± 0.013 0.500 ± 0.015
Soil 4 9.37 ± 0.05 8.89 ± 0.01
Soil 5 1.59 ± 0.04 1.36 ± 0.04
Soil 6 0.685 ± 0.023 0.640 ± 0.008

Fertilizer...

Scope of Parameters
TC = TOC + TIC
TC = NPOC + POC + TIC
TC=Total Carbon
TOC=Total Organic Carbon
TIC=Total Inorganic Carbon
NPOC=Non Purgeable Organic Carbon
POC=Purgeable Organic Carbon
TNb=Total bound Nitrogen

Integrated Autosampler
Automatic sample dosing, automatic sample
changing
• 32 position sampler, 40 ml vials, accepts TOC
certified vials, stirrable, automatic external
acidification for NPOC determination
• 50 position sampler, 12 ml vials, stirrable,
automatic external acidification for NPOC
determination
• 80 position sampler, 7 ml vials, manual external
acidification for NPOC determination
• Suspension method possible

Real High Temperature Combustion
• Temperature programmable up to 1100°C
• High precision sample dosing
• Every part easily acccessible from the front side
• No tools required for maintenance work
• Automatic observation of maintenance intervals

Matrix Separation
Ash finger collects
salt, particles
Catalyst remains
clean

Nitrogen Analysis
• TNb: Total bound Nitrogen, includes all kinds of nitrogen compounds
except N2
• Nitrogen is converted to NO, this reaction requires high temperatures
(< 750°C not sufficient for full recovery)
• 3 detectors available
• IR: maintenance-free, high dynamic range
• Electrochemical cell: high sensitivity, most economic solution
• Chemoluminescence Detector: high sensitivity

Soil Eluates
• Challenge: high salt content from eluent
• Injection volume 0.5ml, combustion
temperature 850°C; automatic external
acidification
• Simultaneous TNb and TOC determination
• No clogging observed
TOC in eluates
TOC
[mg/l]
SDr
[%]
TNb
[mg/l]
SDr
[%]
Soil eluate 1
CaCl2 11 g/l
6.67 4.0 na na
Soil eluate 2
K2SO4 87 g/l
71.1 1.78 12.5 11.2
Soil eluate 3
K2SO4 87 mg/l
136 3.53 27.2 7.70

Suspended Solids
• Challenge: High Amount of Non-
Combustible Particles
• Pretreatment by Ultraturrax, Injection
volume 0.2ml, combustion temperature
850°C, Dilution 1:1000
• No sedimentation observed
• no trend in NPOC
NPOC in solids
(suspension method)
Soil
[w-%]
Theor. Value: 0,37%
Sediment
[w-%]
1st Injection 0,377 2,32
2nd Injection 0,362 2,26
3rd Injection 0,391 2,28
Mean 0,377 2,29
SD 0,014 0,03
SDr 3,86% 1,31%

Fully Automated Analysis of Solid Samples
• Only TOC in water analyzer worldwide
with automatic sample feeder for solids
• Sample feeding by reliable ball valve
technique
• Sample carousel with 80-120 positions
• Solids expansion kit for carbon amounts
up to 20mg C abs.

TOC Determination in Solid Samples
• Sample weight approx. 100 mg
• Solid sample wrapped in silver foil,
externally acidified and dried
• Triple determination
• Combustion temperature 900°C
TOC in solids Surface soil
[w-%]
Clay
[w-%]
Theor. Value:
0.139 w-%
1st det. 4,69 0,139
2nd det. 4,77 0,137
3rd det. 4,80 0,142
Mean 4,75 0,140
SD 0,05 0,003
SDr 1,1% 1,85%

Questions?
• Please use chat window
• Dr. Dominik Margraf
• margraf@elementar.de

Total (Organic) Carbon, Nitrogen and Sulfur Elemental Analysis of Soils and Eluates

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