Flow injection spectrophotometric determination of formaldehyde based on its condensation with hydroxylamine and subsequent redox reaction with iron(III)–ferrozine complex

A flow injection (FI) spectrophotometric method is proposed for the determination of low concentration of formaldehyde (HCHO) in liquid media. It is based on the condensation of HCHO with hydroxylamine sulfate, followed by the reduction reaction of iron(III)–ferrozine complex with the residual hydroxylamine to form a purple iron(II)–ferrozine complex (λmax = 562 nm). In the first reaction, hydroxylamine decreases proportionally to the concentration of HCHO, and therefore the produced purple iron(II)–ferrozine complex decreases with increasing HCHO (a negative FI peak is obtained). The detection limit (S/N = 3) was 1.6 μg L−1. The method can be applied to the determination of HCHO in industrial wastewater.