Fast determination of total aldehydes in rainwaters in the presence of interfering compounds

Abstract

C₁–C₅ aldehydes are toxic substances formed by chemical transformation of organic compounds into the atmosphere. Actual methods used to analyze aldehydes in environmental samples are usually slow and complex, whereas there is a need for rapid and frequent monitoring. Here, a simple, fast method for the spectrophotometric determination of the total content of aldehydes in waters has been developed. The method is based on the spectrophotometric determination at 478 nm of hydrazones in an alkaline medium, generating the hydrazon-α-oxiazinic tautomeric forms, which are formed by condensation of aldehydes and 3,5-dinitrobenzhydrazide (3,5-DHBA). We optimized the conditions of the condensation reaction, e.g., 0.05–1.0 mol L⁻¹ H₂SO₄, heating at 95 °C for 10 min, and the procedure of the spectrophotometric determination of the total aldehyde content at pH higher than 11 and λ_max of 478 nm. Those conditions allow the determination of the total aldehyde content in the presence of various interferences, e.g., most ketones including acetone, 2000-fold of anions: HCO₃⁻, CH₃COO⁻, SO₄²⁻, Cl⁻, F⁻ and cations: Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺. The calibration curve was linear in the range of 0.087–13.5 mg L⁻¹ for aldehydes, with R² of 0.99; the limit of detection was 27 μg L⁻¹ (0.9 μmol L⁻¹) and the limit of determination was 87 μg L⁻¹ (3.2 μmol L⁻¹) in terms of formaldehyde. The suggested procedure was successfully applied for the determination of the total aldehyde content in rainwaters and model mixtures with recovery of 97.8–102.7%. The accuracy of the procedure was confirmed by an analysis with a reference method.