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Determination of NH4+ ions using spectrophotometry


Procedure

Dosing of a sample:

If the concentration of NH4+ ions does not exceed 5 mg.L-1, sample 50 mL of the water to be analyzed – otherwise, reduce the test sample and make up to 50 mL with distilled water.

Add 2 mL of the colorless double tartrate solution. Stir.
Add 2 mL of Nessler reagent and stir again.
Wait 10 minutes, then carry out the spectrophotometric measurements at 420 nm after adjusting the absorbance to zero on the instrument.

Refer to the spectrometer data sheet

Blank test:

Carry out a blank test: replace the test sample with distilled water.

Calibration:

It is necessary to draw a calibration line with standard solutions of known ammonium concentrations.
Using several 50 mL volumetric flasks, prepare the aqueous standard solutions of NH4+ at the following concentrations: 0; 0.2; 0.4; 1; 2; 3; 4; 5 mg.L-1 (use long-neck flasks in order to be able to add the double tartrate and Nessler reagent afterwards).
Add 2 mL of double tartrate to each solution. Stir. Add 2 mL of Nessler reagent and stir once again.
Wait 10 minutes, then carry out the spectrophotometric measurements at 420 nm.

Refer to the calibration data sheet

Illustration of a chronometer ≈ 20 minutes / sample
Information pictogram
Practical tip: prepare the sample, the blank test and the calibration solutions at the same time, in order to save time.
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