1. Total Nitrogen

The Total Nitrogen content of solid samples is analysed by Dumas Combustion; using a Thermo FlashEA 1112 Elemental analyser.

Aqueous samples are analysed using Shimadzu TOC/N analyser. This dries and combusts a small aliquot the sample and detects N by chemiluminescence.

2. Organic Nitrogen

The Organic nitrogen content of water can be estimated from the Total Nitrogen content determined using the Shimadzu TOC/N analyser minus the Total inorganic nitrogen (ammonium content + nitrate content)

Organic N = Total N – ((NO₃-N – NO₂-N) +NH₄-N)

3. Total Oxidisable Nitrogen

Total oxidisable nitrogen (TON) (not Total Organic N) is the combination of nitrate and nitrite (-NO3 and -NO2). This is measured in water samples directly and soil samples after an extraction procedure using 1M KCl.

Total Oxidisable Nitrogen = NO₃–N + NO₂–N
Note: Natural water samples do not normally have any Nitrite present in them.

4. Nitrate

Nitrate in waters is usually measured by Ion Chromatography (Dionex) along with Cl and SO₄–S, however if Nitrate and Nitrite are required they are analysed colourimetrically on the Konelab Discrete Anayser.

5. Ammonium

Ammoniacal nitrogen is analysed in water or soil extracts (in 1M KCl) colourimetrically using the Konelab Discrete Analyser.

6. Total Kjeldahl Nitrogen

Plant samples are put through a Kjeldahl digestion using Sulphuric acid and Selenium (as a catalyst). This digestion converts Organic Nitrogen into Ammoniacal nitrogen which is then analysed by colourimetrically on the Konelab Discrete analyser.

Kjeldahl N = Organic N + NH₄-N

Reporting
Nitrogen analysis results can be reported as:-

• Nitrate-N as Nitrate ie ((NO₃–N mg/l) x 4.4286)
• Nitrite-N as Nitrite ie ((NO₂–N mg/l) x 3.286)
• Ammonium N as Ammonium ie ((NH₄-N mg/l) x 1.286)

Summary

Types of N analysis we have techniques for:-

1. Total N in waters and Soils

2. Total Organic Nitrogen (by difference) in waters.

Organic N= Total N – ((NO₃-N – NO₂-N) +NH₄-N)

3. Total oxidisable nitrogen (TON) nitrate and nitrite (-NO₃ and -NO₂) in waters and soil extract (1M KCl).

4. Nitrate in waters
5. Ammonium in waters and soil extract (1M KCl).

6. Total Kjeldahl Nitrogen in plant material.

Aqueous sample Confidence limits and LODs

Soil Extract Confidence limits and LODs