Dosing a sample

For nitrite concentrations below or equal to 1 mg.L^-1, sample 50 mL of the water to be analyzed. If the water contains more nitrites, reduce the test sample and make up to 50 mL with distilled water.

Add 1 mL of diazotization reagent to each sample and stir.
Wait 30 minutes and carry out the spectrophotometric measurement (at 540 nm) after adjusting the absorbance to zero on the instrument.

Blank test

Carry out the blank test by replacing the test sample with distilled water.

Calibration

A calibration straight line is plotted using nitrite calibration solutions of known concentrations. Once they are prepared, proceed exactly as for a water sample (same volume of solution sampled and 1 mL of diazotization reagent added).

 ≈ 45 minutes / sample

Please note: The pH of the solution should be 1.9 (+/- 0.1) after adding the diazotization reagent. If the pH value is over 1.9, the sample volume must be reduced, and an excess of orthophosphoric acid must be added (at 1.5 mol.L^-1) to obtain this pH value, before making up to 50 mL.

Practical tip: prepare the sample, the blank test and the calibration solutions at the same time, in order to save time.