Understanding Ammonia
Monday, 11 June 2012 07:14

Introduction - Ammonia (NH3) is one of the many forms nitrogen takes as it makes its way through the environment. In high enough concentrations, it is toxic to fish and everyone is aware of the unpleasant odor it spreads. In nature ammonia occurs from the decomposition of organic compounds that contained nitrogen (almost all of them) or the hydrolysis of urea (the compound that gives urine its name). Generally speaking, natural sources of ammonia are dispersed far and wide enough that we would never notice it. However, if enough of those natural sources of ammonia are concentrated into one stream (a sewer) it can become a problem in the water source.

Method Summary – The distillation consists of heating an alkaline buffered solution and condensing the vapors into a mildly acidic trapping solution. The ISE analysis utilizes a standard ammonia ISE to detect ammonia in solution. The phenate method reacts alkaline phenol and hypochlorite with ammonia. This forms indophenol blue with an intensity proportional to the amount of ammonia present. The color intensity is measured photometrically to determine the final concentration.

What You Should Know – To distill or not to distill is always the biggest question with this method. The current (as of this writing) table in 40 CFR part 136.3 has the following note about distillation: “Manual distillation is not required if comparability data on representative effluent samples are on file to show that this preliminary distillation step is not necessary: however manual distillation will be required to resolve any controversies.” There are two things to note about this –

  • Only effluent samples are mentioned as being potentially exempt and
  • If there are any controversies you will have to distill anyway to resolve them

Additionally, if you are using ISE, you will have to prepare your standards in a matrix to match the level of dissolved ions in your samples. If you are using the phenate method you will need to correct for turbidity and/or color as well as pH match your standards to your samples.

Click here for a more detailed Lab Matters PDF on Understanding Ammonia


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