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Sensitive Detection, Selective Determination, and Removal of Nitrite from Water Using the Reactive Function Group of Polyurethane Foam

Abstract A simple and sensitive spectrophotometric method for the microdetermination of nitrite has been developed. This method is based on the reaction of nitrite with primary amine formed on polyurethane foam by (PUF) hydrolysis with hydrochloric acid, to form a diazonium salt, which couples with α‐naphthylamine, α‐naphthol, β‐naphthol, 8‐hydroxyquinoline, resorcinol, or catechol. Introduction of primary amine group on polyurethane foam is also tried via a nitration step followed by reduction of nitro groups with zinc dust in acid media. The purple azo dye formed on the surface of the foam material is used for quantitative and/or semiquantitative determination of submicrogram amounts of nitrite spectrophotometrically or visually, respectively. As low as 0.3 ng · /ml−1 of nitrite is easily detected and Beer's law is obeyed in the concentration range 0.5–100 µg · l−1 at λmax 530 nm with molar absorptivity of 3.5 × 106 l · mol−1 · cm−1 for using α‐naphthylamine as coupling agent. The method is optimized for acidity, time of coupling required, sorption isotherm, and the tolerance amount of other ions. The average sorption capacity of a different type of PUF 0.29 mmol · g−1, preconcentration factor value ≈100, and 100% recovery were obtained (RSD ≈ 2.11%). The method has been applied to various real samples.