The method based upon the reduction of iron(III) solutions in the presence of sulphuric acid, boiling, and subsequent titration in the cold with standard 0.1N potassium permanganate frequently yields high results unless the experimental conditions are closely controlled:

2NH₂OH + 4Fe³⁺ = N₂O+ 4Fe²⁺+ 4H⁺+ H₂O

Better results are obtained by oxidation with potassium bromate in the presence of hydrochloric acid:

NH₂OH + BrO₃^- = NO₃^- + Br^- + H⁺ + H₂O

The hydroxylamine solution is treated with a measured volume of 0.1N potassium bromate so as to give 10-30 mL excess, followed by 40 mL of 5M hydrochloric acid. After 15 minutes the excess of bromate is determined by the addition of potassium iodide solution and titration with standard 0.1M sodium thiosulphate.