This presentation explores a new method of measuring total nitrogen (TN) using a TOC analyzer. Techniques, benefits and results are discussed. For more information, visit ssi.shimadzu.com. Thanks for viewing.

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A New Method for the Determination of
Total Nitrogen in Aqueous Samples
William Lipps
Analytical Measuring Instrument Division
Shimadzu Scientific Instruments, Columbia, Md., USA

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Current EPA Definition for Total Nitrogen
Requires Two Methods
Measure
TKN
Measure
NO3/NO2-N TN

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Must Use 40 CFR Part 136 Methods for
CWA Reporting
• Manual digestion!
• Manual distillation!
• Nessler, IC, titration, ISE, phenate!
TKN Methods!
• Manual digestion!
• Automated distillation/diffusion!
• Direct colorimetry!
TKN Methods!
• IC, reduction colorimetry!
NO3/NO2 –N
Methods!

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The “Classical” Kjeldahl Reactions
Distilled and Titrated Ammonia
Digestion
• H2SO4 + 2(NH2)2CO - (NH4)2SO4 +2 CO2
Distillation
• (NH4)2SO4 + NaOH - NaHSO4 + H2O + 2NH3
Capture
• H2SO4 + 2NH3 - (NH4)2SO4 + H2O
Titration
• H2SO4 + NaOH - NaHSO4 + H2O

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Present Day TKN Methods Can Either
Distill (Diffuse) or Measure NH4
+ in the Matrix
Manual Digestion
• H2SO4 + (NH2)2CO - (NH4)2SO4 + 2CO2
• Must use catalyst
Distillation (required for some methods)
• (NH)4SO4 + NaOH - NaHSO4 +H2O + 2NH3
Detection
• Titration, ISE, manual colorimetry, automated
colorimetry

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Kjeldahl Method!
Substance +
Conc. H2SO4
+ CuSO4
+ K2SO4
Image: Wikipedia
1 Liter RB
Flask
Water
out
Water
in Conical Flask

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Operational Comparison of TKN Methods
Manual Digestion
Distillation
Followed By:!
Require Final
Digest Volume!
Require Final
Distillate Volume!
Titration! no! no!
Ion Selective
Electrode!
no! yes!
Manual Phenate! no! yes!
Automated
Phenate !
no! yes!
Block Digestion!
Automated
Salicylate!
yes! N/A!

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Techniques for Analysis of Total Nitrogen
(EPA Only Approves TKN)!
Manual Digestion
Distillation Followed By:!
MDL (mg/L)!
Titration! 1.0 !
Manual Phenate! 0.05 ?!
Ion Selective Electrode! 0.03!
Automated Phenate! 0.01!
Block Digestion!
Automated Salicylate! 0.1!
Auto-GD/pH colorimetry! 0.2!
Auto-GD/Salicylate! 0.02!

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Some Problems With TKN Method for TN
Time consuming – 0.5 – 2 hour digestion
• Separate distillation and/or analysis
Uses hazardous reagents
• Boiling sulfuric acid
• Metal catalyst
Must run NO3 + NO2 separately
Not applicable to all N compounds

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TKN Recovery in Various N Compounds

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New Method is Needed That Measures
Total Nitrogen As Single Result
Organic
Nitrogen!
NH3-N! NOx-N! TN!
This method can be a lab or online method

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Any New Method for TN Should…
Obtain equivalent results to TKN and other TN methods
Be “rugged”
Use few reagents
Have a large dynamic range
Sample/”handle” a complex matrix

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Total Nitrogen Can Be Easily Measured on
TOC Analyzer
Catalytic Combustion (CC)
• 2(NH2)2CO +5O2 + catalyst à 4NO + 4H2O + CO2
Ozonation
• NO + O3 à NO2 + O2!
• NO + O3 à NO2* + O2!
Detection
NO2* à NO2 + light !

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TOC + TN Analyzer!

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Schematic of TOC + TN Analyzer
TN Analysis

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Total Nitrogen Measurement is
Rugged and Uses Few Reagents
Measure the sample (dilute)
Decomposition : 720℃ with Pt
catalyst
Formation of NO
Formation of NO2
* , - NO2, Photon
O2 from air
Ozone
Emission
Obtain the TN Result (every 5 minutes)
Electricity

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Comparison of TN to TKN!
TN TKN
Measurement
contains
- Ammonia
- Nitrate
- Nitrite
- Organic nitrogen
compounds
- Ammonia
- Organic nitrogen
compounds
Consumables Catalyst
hydrochloric acid
Mercury or
selenium, sulphuric
acid
Analysis time
3-7 min (together
with TOC
measurement)
Minimum 60 min
Online realization Easy Not possible

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TKN and Catalytic Oxidation Recovery in
Various N Compounds!

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Comparison of TN to TKN (QC Samples)!

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HTCO Methods Obtain Near Equal Results with
Persulfate TN on Unknown Samples

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Recovery (%) of Various Nitrogen
Compounds

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Recovery of TN with Concentration !
150 microliter sample!

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Recovery of TN with Concentration!
300 microliter sample !

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Total Nitrogen 300 Microliter Sample!

25. WK46665
Standard Test Method for Total Nitrogen in Water by
High-Temperature Catalytic Combustion and
Chemiluminescence Detection
This test method is under the jurisdiction of ASTM Committee D19 on Water and
is the direct responsibility of Subcommittee D19.06 on Methods for Analysis for
Organic Substances in Water.
Current edition approved [date to come]. Published [date to come]. DOI:10.1520/
Dxxx-xx.
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Standard Test Method

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If Kjeldahl Was Alive Today, He Would
Have a Shimadzu

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