• Standard laboratory equipment, in particular: volumetric flasks, spectro cuvettes, Erlenmeyer flasks
• A spectrophotometer
• Orthophosphoric acid solution (H₃PO₄) at 1.5 mol.L^-1
• Diazotization reagent^*
• Nitrite aqueous solution at 100 mg.L^-1 (stock solution)
• Nitrite calibration solution at 1 mg.L^-1

^* Composition for 1 L:
    100 mL of orthophosphoric acid
    2 g of dichloride of N-(naphtyl-1) diamino-1,2 ethane
    40 g of amino-4 benzenesulfonamide
    Ultrapure water to make up to 1 L