Spectrophotometric determination of formaldehyde with chromotropic acid in phosphoric acid medium assisted by microwave oven

In the present study, a spectrophotometric method for the determination of formaldehyde by using chromotropic acid was devised, in which the use of potentially hazardous and corrosive concentrated sulfuric acid was eliminated and advantageously replaced by a mixture of H₃PO₄ and H₂O₂. The reaction between formaldehyde and chromotropic acid (CA) in a concentrated phosphoric acid medium was accelerate by irradiating the mixture with microwave energy for 35 s (1100 W), producing a violet-red compound (λ_max=570 nm). Beer's Law is obeyed in a concentration range of 0.8-4.8 mg l⁻¹ of formaldehyde with a good correlation coefficient (r=0.9968). The proposed method was applied in the analysis of formaldehyde in commercial disinfectants. Recoveries were within 98.0-100.4%, with standard deviations ranging from 0.03 to 0.13%.