Total Nitrogen and Total Kjeldahl Nitrogen

The total nitrogen is the sum of the nitrate nitrogen (NO3-N), nitrite nitrogen (NO2-N), amine nitrogen (NH4-N) and organic bounded nitrogen structures. However, total nitrogen and total kjeldahl nitrogen are not same. Because, the total kjeldahl nitrogen is the sum of the organic bounded nitrogen groups and the ammonium-nitrogen (it is defined as NH4-N at the ionic state and defined as NH3-N at the non-ionic state). Besides, total kjeldahl nitrogen does not contain nitrite-nitrogen and / or nitrate-nitrogen.

The nitrogen structures mentioned as organic bounded nitrogen are represented as organic bonded compounds formed with trivalent state nitrogen. Organic bounded nitrogen compounds can contains different nitrogen states. For example, peptides, proteins, nucleic acids, urea and nitrogen-containing pesticides (known as synthetic organic compounds) contain trivalent state nitrogen. For analytical calculations, the sum of organic bonded compounds formed with trivalent state nitrogen and ammonium-nitrogen can be considered as total kjeldahl nitrogen.

According to the explanations above, we can say that total kjeldahl analysis method is valid for the determination of nitrogen at the trivalent state. On the other hand total kjeldahl analysis method cannot be evaluated for azide, azo, nitroso, azine, cyanide, nitrite and nitrate structures.