SOP: Determination of Albuminoid Nitrogen in Water
GIFSQ — Global Institute for Food Safety & Quality
Principle
Albuminoid nitrogen is a measure of proteinaceous nitrogen present in water and indicates organic pollution in a water supply. It is largely derived from animal and plant life which are normal to aquatic environments. After the determination of ammonia nitrogen, if a strong solution of alkaline potassium permanganate is added to the residual sample and distilled, any supplementary release of ammonia indicates the presence of albuminoid nitrogen. It is formed mainly by the action of potassium permanganate on the unsubstituted amino groups of many amino acids, polypeptides and proteins in an alkaline medium. The ammonia evolved may be determined either by nesslerization or by absorption in boric acid and titration with a standard solution of a strong mineral acid, as described under ammonia nitrogen.
Reagents
In addition to the reagents given under the ammonia nitrogen method, the following reagent is required.
a. Alkaline potassium permanganate: in a 3-litre Corning beaker, dissolve 16 g of KMnO₄ in sufficient ammonia-free distilled water; add 288 g of NaOH or 404 g of KOH and enough ammonia-free water to make up to 2.5 litres; concentrate to 2 litres on a hot plate. Determine the ammonia blank in 50 ml of the reagent and use the result as a basis for correction in subsequent determinations.
Procedure
Proceed for the estimation of the albuminoid nitrogen determination immediately following the ammonia nitrogen determination on the same sample
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If 500 ml of sample has been taken, and 150 to 200 ml has been distilled over for the estimation of ammonia nitrogen, distil off a further 50 to 100 ml
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Add a few pieces of recently ignited pumice, or short pieces of capillary glass tubing each sealed at one end, to prevent bumping
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Add 50 ml of alkaline potassium permanganate reagent and continue distillation
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Collect three successive 50-ml portions of the distillate and estimate the ammonia by nesslerization as described under the ammonia nitrogen method
Calculation
Calculate the albuminoid nitrogen as ammonia nitrogen was calculated. Correct for the blank of the alkaline permanganate solution, instead of the phosphate buffer solution.
References
- Phelps, E.B., J. Infect. Dis., 1, 327 (1904).
- Standard Methods for the Examination of Water and Wastewater, 13th edn., American Public Health Association, Washington D.C., p. 221 (1971).