Soil samples are analysed by extracting the sample with potassium chloride and analysing this extract. This analyte is variously called ammoniacal nitrogen, available ammonium, and exchangeable ammonium depending upon the literature that is referenced.
As an environmental chemistry team, nitrogen compounds really are a focus for us and we like to support our clients, where possible with as much information as possible about the substances they are dealing with.
Free ammonia (NH3) can be present in water as dissolved ammonia or as the dissolved ammonium ion (NH4). If the pH value is less than 8.0 then the ammonia/ammonium equilibrium is such that the majority of ammonia will be present as the ammonium ion and measurable quantities of free ammonia are unlikely to be present in the sample. In the case of leachate preparation, unless the soil is sufficiently alkaline to raise the pH of the leachant to >8.0, then any ammonia present in the soil will be converted to ammonium during the leaching process.
Total Nitrogen and Kjeldahl Nitrogen
Kjeldahl nitrogen measures organic nitrogen and ammoniacal nitrogen, whereas total nitrogen will include all forms of nitrogen, including nitrate and nitrite (not measured by Kjeldahl).
Total Oxidised Nitrogen (TON)
Our total oxidised nitrogen service includes analysis of nitrate and nitrite, but please note that nitrite will tend to oxidise to nitrate in aerobic conditions.
Organic Nitrogen Compounds
These are substances such as amines, pyrroles, nitrobenzenes etc. Organic nitrogen is quantified by subtracting ammoniacal nitrogen from the Kjeldahl nitrogen value.
Analysis of Nitrogen Compounds
We express all nitrogen species as N to allow direct comparison of data. Ammoniacal Nitrogen: NH3 (ammonia) and NH4 (ammonium), total oxidised nitrogen (TON) are analysed by discrete colorimetric analysis.
- Soils are determined by Elemental analysis, using thermal conductivity following combustion.
- Waters are determined Spectrophotometrically
- Elemental analysis by thermal conductivity after combustion.
- Kjeldahl Nitrogen: Organic and ammoniacal nitrogen converted to ammonium sulphate by wet oxidation. The ammonium sulphate concentration can be determined spectrophotometrically or by titration.
Nitrogen Compounds in the Environment
Ammonium is by product of town gas manufacture and the coking process. Ammonia is also produced by the degradation of waste in landfills; landfill leachates contain very high levels of ammonia. Discharge of ammonium to surface water can result in significant reduction in oxygen levels as the ammonium oxidises to nitrate and nitrite. This has a significant detrimental impact on the aquatic environment.
Nitrates and ammonium are constituents of fertilizers and can be found in surface water run-off. High nitrate levels in water can lead to Blue Baby syndrome, the nitrates being converted to nitrite by the digestive system which reacts with the haemoglobin of the blood and inhibits oxygen uptake.