4. A SPECTROMETRIC DETERMINATION OF
AMMONIUM IONS IN A WATER SAMPLE

Use a one-point calibration and determine the concentration of ammonium ions in a water sample.

NH₄⁺+ OH^– NH₃ + H₂O
NH₃ + OCl^– NH₂Cl + OH^–

+ NH₂Cl

Na₂[Fe(CN)₅NO]

+
	Indophenol (blue coloration)

*For reagent preparation please contact natasa.gros@fkkt.uni-lj.si.

Hazards

	Phenol is corrosive and toxic: it causes severe irritation of the upper respiratory tract and is harmful if absorbed through the skin. Avoid inhalation and skin contact. R: 24/25-34, S: 28.2-45

	Phenolic reagent contains sodium nitroprusside dihydrate (disodium pentacyanonitrosylferrate(III) dihydrate). This can cause respiratory-tract and skin irritation. Avoid contact. R: 26/27/28-32, S: 7-28-29-45
	Sodium hypochlorite causes chemical burns to the respiratory tract. It can also cause skin burns, and when in contact with acids it liberates toxic gases. R: 31-34, S: 28-45-50.1
	Sodium hydroxide causes skin burns. It can also cause a skin rash (in milder cases), and cold and clammy skin with cyanosis or a pale colour. R: 35, S: 26-37/39-45

For the blank, the standard and the sample, follow the procedure as given below.

	Blank	Standard	Sample
Deionised water	1	/	/
Ammonium chloride standard solution	/	1	/
Sample	/	/	1
Phenolic reagent	4	4	4
Mix thoroughly.
Hypochlorite solution	4	4	4

Mix thoroughly, measure after thirty minutes using the red LED.

Write the measurements in the table blow and calculate the absorbance.

Calculation of the results:

Calculate the final result and enter it under the serial number of the sample in the table “Results – Contaminants”.

The guide value for ammonium in drinking water which is set by the EU Drinking Water Directive (Council Directive 98/83/EC) is 0.5 mg/L.