Determination of NH4+ ions using spectrophotometry
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.
Carry out a blank test: replace the test sample with distilled water.
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.