Ammonia (NH3) vs Ammonia Nitrogen (NH3-N)

Question

I've been looking into chloramination (chlorine & nitrogen reactions) and noticed many papers either reference Ammonia (NH3) or Ammonia-Nitrogen (NH3-N), seemingly interchangeably.

Is the hyphenation simply nomenclature for "we are only interested in measuring the nitrogen component of ammonia" or does NH3-N present as a distinct compound in water treatment?

For example, if a paper provides a Cl2:N Ratio of NH3, is this equivalent to a Cl2:N ratio of NH3-N?

Note: Asking in parallel to my 'as xxx' question. Posting separately to avoid convolution.

Answer 1

$\ce{-}$ in $\ce{NH3-N}$ is just a hyphen, not a chemical bond, with meaning "nitrogen present in form of $\ce{NH3}$ or $\ce{NH4+}$". It can have both qualitative and quantitative meaning.

With rounded molar masses, $\pu{17(18) mg L-1}\text{ of }\ce{NH3(NH4+)} \equiv \pu{14 mg L-1}\text{ of }\ce{NH3-N}$.
Or $\ce{N-NH3}$, AFAIK the convention is not settled.

There can be literally any compound or material instead of $\ce{NH3}$ in the $\ce{X-N}$ syntax, containing $\ce{N}$. $\ce{NO2-N}$, $\ce{NO3-N}$, $\ce{Org-N}$ are very common too, e.g. in context of waste water analysis.

That syntax convention is often used in elemental analysis, where are determined contents of particular forms of nitrogen, recalculated to element content.

The respective molar ratios are the same for ammonia and ammonia nitrogen, as there is 1 nitrogen atom in ammonia molecule. For mass ratios, they have to be multiplied by molar mass ratios.

The topic is related to the more general principle not limited to chemistry: quantities being expressed by an equivalent quantity of something else.

• E.g. spring scales, commonly used on farmer markets, measure an object weight = force. But, they are calibrated in the equivalent mass. So an object with weight $\pu{9.806 N}$ has this weight reported "as mass" $\pu{1 kg}$.
• The content of phosphorus or potassium in solid fertilizers is for historical reasons often reported as $\ce{P2O5}$ and $\ce{K2O}$ content, even if there are no such oxides present. ($\ce{N}$ context is addressed by Nilay Ghosh).

Answer 2

Based on the context of question, the correct term for it is ammoniacal nitrogen. Most of the things are explained in @Poutnik's answer, so I am going to expand the last point. This term is also used in fertilizer domain. It used to refer a nitrogen source where most of the nitrogen will come from ammonia. The other form of nitrogen are nitrate-nitrogen and urea-nitrogen. It is slower acting than the nitrate form. It must be converted by soil acting bacteria to nitrate nitrogen before it can be absorbed by plant roots. It is not as easily lost from the soil by leaching.

Please refer to this article:

1. https://www.teagasc.ie/crops/soil--soil-fertility/fertiliser-types/nitrogen-n/
2. https://www.canr.msu.edu/news/understanding-the-forms-of-nitrogen-in-water-soluble-fertilizers-for-greenhouse-growers